Alex Harui is the guru of turning a Flex 4 Spark List into a look-alike for the old Flex 3 component using skins and a custom ItemRenderer. Alex has used List + ItemRenderer to make a DataGrid, DateField, ColorPicker, Menu + MenuBar, and even an XML-based TreeList. Unfortunately, Alex’s TreeList assumes incoming XML, and I needed a TreeList that could display a simple object hierarchy (root node with children, and those children have children, etc.). Since I couldn’t find exactly what I wanted, I decided to build it myself.

Flattener

The key step to getting a hierarchy of objects to display as a list is: flatten the list, duh! Or at least flatten the part of the tree you wish to display. So, I built a simple adapter class that turns an object hierarchy into an ArrayList that can be given directly to a List‘s dataProvider.

Here’s the actual flattener, but with just the comments not the code:

public class MyObjFlattenedList extends ArrayList {
 
    //the root object
    private var _root:MyObj;
 
    //list of open nodes
    private var _openList:Array;
 
    public function MyObjFlattenedList(root:MyObj) {
        _root = root;
        _openList = [];
        reset();
        ...
    }
 
    public function reset(openList:Array = null):void {
        //init the flattened list, starting at root
        _openList = (openList == null ? [] : openList);
        var a:Array = [];
        addItemToList(_root, a);
        this.source = a;
    }
 
    private function addItemToList(obj:MyObj, a:Array):void {
        //recursively walk obj and all of its "open" children to build
        //a flattened list that is returned in array a
    }
 
    public function isItemOpen(obj:MyObj):Boolean {
        //true if obj has children and is "open"
    }
 
    public function openItem(obj:MyObj):void {
        //add all of obj's children (if any) to the list
    }
 
    public function closeItem(obj:MyObj):void {
        //remove all of obj's children (if any) from the list
    }
    ...
}

There’s really not much to it. When instantiated with a root object, the object hierarchy is walked recursively to build a flattened list of all the open nodes. Once the initial list is built, openItem() can be called to open a node, and add all its children to the list. Alternately, closeItem() can be called to close a node, and remove all its children from the list.

Design

I used some basic styling and skinning, but the ItemRenderer does the majority of the work. Here’s the abbreviated version of MyObjRenderer.mxml with all the boring stuff edited out:

<?xml version="1.0" encoding="utf-8"?>
<s:ItemRenderer
    xmlns:fx="http://ns.adobe.com/mxml/2009" 
    xmlns:s="library://ns.adobe.com/flex/spark"
    width="100%"
    autoDrawBackground="false">
 
    <fx:Script>
        <![CDATA[
            [Bindable] private var _obj:MyObj;
            [Bindable] private var _hasChildren:Boolean = false;
 
            private var _list:MyObjFlattenedList;
 
            override public function set data(val:Object):void {
                super.data = val;
 
                if (val != null) {
                    _obj = val as MyObj;
 
                    var ownerList:List = owner as List;
                    _list = ownerList.dataProvider as MyObjFlattenedList;
 
                    btn.selected = _list.isItemOpen(_obj);
                    _hasChildren = (_obj.children != null && _obj.children.length > 0);
                }
            }
 
            private function toggleHandler():void {
                if (btn.selected) {
                    _list.openItem(_obj);
                } else {
                    _list.closeItem(_obj);
                }
            }
        ]]>
    </fx:Script>
 
    <s:states>
        <s:State name="normal" />
        <s:State name="hovered" />
        <s:State name="selected" />
    </s:states>
 
    <s:Rect ...>
 
    <s:HGroup ...>
        <s:ToggleButton id="btn" click="toggleHandler()" visible="{_hasChildren}" ... />
 
        <s:Group id="dot" visible="{!_hasChildren}" ... />
 
        <s:Label ... />
    </s:HGroup>
</s:ItemRenderer>

Each rendered item has a background Rect and a Label. But most importantly, each row has either a ToggleButton (if the object has children) or some non-interactive visuals (if the object doesn’t have children it just gets a dot). The toggle button is the key interactive element used to open or close the node, everything else is part of the visual gravy added to make the list look good.

Focusing on the functional stuff, if you look in the script block, you’ll see two functions: a data() setter and a toggleHandler() to handle toggle button clicks. As expected, clicking the toggle button calls openItem() or closeItem() on the flattener adapter which adds or removes children from the flattened list, respectively. The setter mostly sets up the local variables, but it notably computes if the object has children or not, and also sets the initial state of the toggle button.

Conclusion

With just a little effort, we can have a nice usable Spark TreeList component that looks decent. More importantly, we have total control and can make the TreeList look like anything our designer can throw at us. As is always the case, the combo of List + ItemRenderer proves to be awesome. I tried to cover all the interesting pieces, but for the details, you’ll need to check out the source code.

Here’s the finished product (view source enabled):

Use it and enjoy.

Files

• ObjTreeList (fxp download)

The fancy clock skin overlays a very simple clock component. The Clock component is quite underwhelming, but here it is in all of its abbreviated glory:

public class Clock extends SkinnableComponent {
    public var secAngle:Number = 0.0;
    public var minAngle:Number = 0.0;
    public var hourAngle:Number = 0.0;
    private var _timer:Timer;
    private var _tween:GTween;
 
    public function Clock() {
        ...
        _tween = new GTween(this, 2, ...);
        _timer = new Timer(2000,30);
        _timer.addEventListener(TimerEvent.TIMER, tickHandler);
    }
 
    private function tickHandler(e:TimerEvent):void {
        var t:Date = new Date();
 
        var h:Number = t.getHours();
        var m:Number = t.getMinutes() + h * 60;
        var s:Number = t.getSeconds() + m * 60;
        var ms:Number = t.getMilliseconds();
 
        _tween.proxy.secAngle = -90 + s * 6 + ms * 0.006;
        _tween.proxy.minAngle = -90 + s * 0.1;
        _tween.proxy.hourAngle = -90 + (s / 120);
    }
    ...
}

At the core of the Clock component is a single timer. When the timer fires, it uses the current date to compute the angle of the hour hand, minute hand, and second hand. The actual motion of the hands is managed via the awesome proxy functionality in Grant Skinner’s GTween library.

All the interesting FXG action takes place in the skin, so let’s check it out:

<?xml version="1.0" encoding="utf-8"?>
<s:Skin
        xmlns:fx="http://ns.adobe.com/mxml/2009"
        xmlns:s="library://ns.adobe.com/flex/spark"
        creationComplete="complete()">
 
    <fx:Metadata>
        [HostComponent("components.Clock")]
    </fx:Metadata>
 
    <fx:Script>
        <![CDATA[
            private function complete():void {
                ...lots of programmatic FXG here...
            }
        ]]>
    </fx:Script>
 
    ...lots of vanilla FXG here...
 
    <s:Path rotation="{hostComponent.minAngle}" ...
    <s:Path rotation="{hostComponent.hourAngle}" ...
    <s:Path rotation="{hostComponent.secAngle}" ...
</s:Skin>

Getting data to the skin is done via the standard binding to hostComponent. There is no need for the more complicated partAdded() and partRemoved() mechanism, because the Clock component is not intended for general use, unlike my previous components: Terrific TabBar, SuperTextInput, and Drawer.

The skin has a big block of programmatic FXG skinning, done in actionscript code inside the complete() handler which is fired by the creationComplete event. It also has a big block of vanilla MXML declarative FXG skinning, which, most importantly, includes the clock hands and the previously mentioned binding to hostComponent.

By its nature, a clock has a lot of identical elements that are positioned in a circle. The obvious attack is to put the repeated elements in a loop, or set of loops, and go the programmatic route to construct the skin. For example, the long thin ticks along the outer ring are constructed with a double loop. Here’s the relevant snippet of code from inside the complete() handler:

for each (var i:int in [0,30,60,90,120,150,180,210,240,270,300,330]) {
    for each (var j:int in [6,12,18,24]) {
        var p:Path = new Path();
        p.data = "M 174,-0.5 L 184,-0.5 184,0.5 174,0.5 Z";
        p.x = 250;
        p.y = 250;
        p.rotation = i + j;
        p.fill = gray;
        this.addElementAt(p, 1);
    }
}

A new Path element is created and its data property is set. Our tick mark is 10px long, but only 1px wide. With each iteration, a tick mark is created and rotated into place. There are two important tricks in this code that are worth pointing out. First, the rotation origin is at (0,0) for each element, so we must construct our path from -0.5 to 0.5 for it to rotate correctly. Second, we must use addElementAt() to place each element into the proper layer of the drawing because the programmatic FXG code runs after all the vanilla (aka non-programmatic) FXG has been drawn.

Conclusion

No one in their right mind would ever build a clock skin like this. To do this the right way, you’d definitely want to use an image or two to construct the skin. The only reason I went the programmatic FXG skinning route was to verify to myself that it could be done. So, yes it can be done, and I enjoyed the trip.

Files

• AnalogClock (download)

Extend TabBar and TabBarButton

I just want to build your average web browser tab in Flex 4, no more, no less. Browser tabs have two cool features: each tab has a close button, and the tabs can be reordered by dragging. Actually, I just lied about the no less part, because I’m going to ignore dragging and focus my attention on the closeable tab part. Please see my previous post on drag-and-drop in Flex 4 if you are interested in the dragging part.

A TabBar is just a bag of tabs, where each individual tab is a button, or a TabBarButton to be more precise. To create a closeable tab, we need to add a new button that can be clicked to close the tab, duh. And this is in addition to the default behavior of clicking the tab to select it. Since we are disciples of The Flex 4 Way of building custom components, we know this means we must extend TabBarButton and add a new Button SkinPart to it:

package components {
    ...
 
    public class TerrificTabBarButton extends ButtonBarButton {
        [SkinPart(required="false")]
        public var closeButton:Button;
 
        private var _closeable:Boolean = true;
 
        public function TerrificTabBarButton() {
            super();
 
            //IMPORTANT: this enables the button's children (aka the close button) to receive mouse events
            this.mouseChildren = true;
        }
 
        [Bindable]
        public function get closeable():Boolean {
            return _closeable;
        }
        public function set closeable(val:Boolean):void {
            if (_closeable != val) {
                _closeable = val;
                closeButton.visible = val;
                labelDisplay.right = (val ? 30 : 14);
            }
        }
 
        private function closeHandler(e:MouseEvent):void {
            dispatchEvent(new TerrificTabBarEvent(TerrificTabBarEvent.CLOSE_TAB, itemIndex, true));
        }
 
        override protected function partAdded(partName:String, instance:Object):void {
            super.partAdded(partName, instance);
 
            if (instance == closeButton) {
                closeButton.addEventListener(MouseEvent.CLICK, closeHandler);
                closeButton.visible = closeable;
            } else if (instance == labelDisplay) {
                labelDisplay.right = (closeable ? 30 : 14);
            }
        }
 
        override protected function partRemoved(partName:String, instance:Object):void {
            super.partRemoved(partName, instance);
 
            if (instance == closeButton) {
                closeButton.removeEventListener(MouseEvent.CLICK, closeHandler);
            }
        }
    }
}

First, we have the closeButton SkinPart and it’s closeHandler() event handler. Wiring the handler function to the button is done in the partAdded() override, and un-wiring in the partRemoved() override. The handler just bubbles a closeTab custom event which will be handled by the parent TabBar. Next, we use the closeable property to manage the close button’s visibility. Finally, an additional button visibility check is necessary in partAdded() to set the initial visibility.

There are two other interesting pieces of code. One, we must set mouseChildren = true in the constructor to enable our button within a button to receive and respond to mouse events. Two, in a somewhat hackish fashion, I add or remove padding from the tab’s label when the close button is present or not.

Now that we have a nice close button on the individual tabs, we extend TabBar to make a pretty API for managing tabs and their new functionality. Here is an abbreviated TerrificTabBar component showing the relevant public methods:

package components {
    ...
 
    public class TerrificTabBar extends TabBar {
        public function TerrificTabBar() {
            super();
        }
 
        public function setCloseableTab(index:int, value:Boolean):void {
            if (index >= 0 && index < dataGroup.numElements) {
                var btn:TerrificTabBarButton = dataGroup.getElementAt(index) as TerrificTabBarButton;
                btn.closeable = value;
            }
        }
        public function getCloseableTab(index:int):Boolean {
            if (index >= 0 && index < dataGroup.numElements) {
                var btn:TerrificTabBarButton = dataGroup.getElementAt(index) as TerrificTabBarButton;
                return btn.closeable;
            }
            return false;
        }
 
        private function closeHandler(e:TerrificTabBarEvent):void {
            closeTab(e.index, this.selectedIndex);
        }
 
        public function closeTab(closedTab:int, selectedTab:int):void {
            ...
        }
 
        protected override function partAdded(partName:String, instance:Object):void {
            super.partAdded(partName, instance);
 
            if (instance == dataGroup) {
                dataGroup.addEventListener(TerrificTabBarEvent.CLOSE_TAB, closeHandler);
            }
        }
 
        protected override function partRemoved(partName:String, instance:Object):void {
            super.partRemoved(partName, instance);
 
            if (instance == dataGroup) {
                dataGroup.removeEventListener(TerrificTabBarEvent.CLOSE_TAB, closeHandler);
            }
        }
    }
}

There is a public getter and setter for toggling the close-ability of individual tabs, setCloseableTab() and getCloseableTab(). And also a public method for closing a tab, closeTab(), which can be used to force close an un-closeable tab. Additionally, closeTab() is used internally to close a tab when its close button is clicked. As is standard, the wiring and un-wiring of the closeHandler() handler function is done in the partAdded() and partRemoved() overrides.

Very vanilla, but there is one interesting part worth mentioning. I made the decision to attach the listener to the dataGroup property of TabBar, this is the default container of individual tabs (aka TerrificTabBarButtons). Yes, I could just as easily have attached the handler directly to TabBar in the constructor and used weak references. But after having built enough custom Flex 4 components, it feels funny to me to do any event wiring outside of partAdded() and partRemoved(). Thus, I made the decision to attached to dataGroup. Without doing a bunch of testing (which I haven’t done), I can’t say if this is better or worse from a memory or performance perspective, I just like the way this code looks better.

Conclusion

I put a pretty skin on everything using some of my favorite drawing tricks, but that’s the subject of a future post. Some brief highlights include:

• I used CSS to wire my components to my skins, so I minimize the use of skinClass attributes for better decoupling
• I used a big negative gap in TerrificTabBarSkin to make the tabs overlap
• I set a maxWidth and a minWidth on the individual tabs in TerrificTabBarButtonSkin, which in combination with maxDisplayedLines="1" on the Label, make the tabs truncate with ... when they get too big
• The curved tab shape is drawn with a Path, but I wrap it with a Group and set the Group‘s scale-9 grid (scaleGridLeft, scaleGridTop, etc.) so it expands and contracts correctly
• The close button’s x is drawn as a + around the coordinate origin, also known as (0,0), and then rotated 45 degrees

Here’s the finished product (view source enabled):

Use it and enjoy.

UPDATE: Jon Rose has written an excellent FlexMonkey Deep Dive article on how to bring a custom component under automation. He uses TerrificTabBar as an example. Thanks Jon.

Files

• TerrificTabBar (download)

SuperTextInput is a prompting, clearable TextInput extension in Flex 4. It’s just an enhanced version of the default TextInput control, and as such, it follows a fairly standard pattern of custom component creation.

Enhanced Component Pattern

It’s almost too stupid to call this a pattern, but it’s so common in custom component creation that I’ll run with it. Also, I’ve found it to be worthwhile to distinguish between adding new functionality to a component already present in the framework (aka an enhanced component) versus creating a truly custom component.

The enhanced component pattern is just two simple steps:

1. Extend – extend some default component and add some new functionality
2. Skin – make it look good

In my version of reality, these steps carry equal weight, because almost all worthwhile functionality in Flex touches the UI in some fashion, so the design and UX (the look-and-feel, it’s usability, the integration into the rest of the app, etc.) are critical. Don’t forget or skimp on step #2 because it’s all the client, team, customer ever sees.

A Prompting TextInput

Since SuperTextInput has two new pieces of functionality (the prompt and the clear button), I’ll split them apart, and consider each part separately. First, the prompt is merely the text you see when the TextInput is empty. It often becomes a space saving label, because it can be used to tell the user what goes into the TextInput without costing the UI any screen real estate.

Thinking more about the prompt, we want the prompt text to be visible initially, but it should disappear when the user clicks (or tabs) to the control, and only returns when the control loses focus and is still empty. So this tells us that we need to communicate both the prompt text and it’s visibility to our skin. The prompt text can just be a simple Label SkinPart, but it’s visibility is complicated enough that it makes sense to add a new prompting SkinState.

Here’s a functioning PromptingTextInput custom component (which is simply the prompting code lifted from SuperTextInput.as):

package components {
    import flash.events.FocusEvent;
    import mx.events.FlexEvent;
    import spark.components.Label;
    import spark.components.TextInput;
    import spark.events.TextOperationEvent;
 
    [SkinState("prompting")]
    public class PromptingTextInput extends TextInput {
 
        [SkinPart(required="false")]
        public var promptDisplay:Label;
 
        private var _prompt:String = '';
        private var _focused:Boolean = false;
 
        public function PromptingTextInput() {
            super();
 
            //watch for programmatic changes to text property
            this.addEventListener(FlexEvent.VALUE_COMMIT, textChangedHandler, false, 0, true);
 
            //watch for user changes (aka typing) to text property
            this.addEventListener(TextOperationEvent.CHANGE, textChangedHandler, false, 0, true);
        }
 
        [Bindable]
        public function get prompt():String {
            return _prompt;
        }
        public function set prompt(value:String):void {
            if (_prompt != value) {
                _prompt = value;
                if (promptDisplay != null) {
                    promptDisplay.text = value;
                }
            }
        }
 
        private function textChangedHandler(e:Event):void {
            invalidateSkinState();
        }
 
        override protected function focusInHandler(event:FocusEvent):void {
            super.focusInHandler(event);
            _focused = true;
            invalidateSkinState();
        }
        override protected function focusOutHandler(event:FocusEvent):void {
            super.focusOutHandler(event);
            _focused = false;
            invalidateSkinState();
        }
 
        override protected function partAdded(partName:String, instance:Object):void {
            super.partAdded(partName, instance);
 
            if (instance == promptDisplay) {
                promptDisplay.text = prompt;
            }
        }
 
        override protected function getCurrentSkinState():String {
            if (prompt.length > 0 && text.length == 0 && !_focused) {
                return 'prompting';
            }
            return super.getCurrentSkinState();
        }
    }
}

In addition to the promptDisplay SkinPart and the new prompting SkinState, there is a lot of other stuff going on in the above code. First, as is typical with data-driven SkinParts, we back the promptDisplay with a good old prompt property. The net is the fairly common pattern of: check if the SkinPart is not null, then do something to it. So in the prompt setter, we assign the incoming value to the private _prompt variable, then check if promptDisplay is available and if yes, set it’s text property. The setter does the job of updating the prompt, but only once everything is happily running. In order to get the data to the skin initially, we must use the partAdded() override to pass the local prompt to the promptDisplay‘s text property. And that’s it for the prompt text.

The prompt visibility part requires lots of event watching, and also SkinState stuff because we made the choice to push visibility via the prompting SkinState. First, we wire up both the programmatic text change events and the user text change events to a handler, textChangedHandler(), that does nothing more than invalidate the state. TextInput change events are a little wacky, but the code works fine. Next, instead of wiring the focus events to another handler (as seen in this prompting TextInput component by Andy McIntosh), we simply override the protected handlers in the parent and add our focus-tracking logic directly. Finally, we override getCurrentSkinState() to do the work of figuring out whether or not the prompt should be displayed.

A skin for PromptingTextInput is now trivial because our component does the work of pushing the important information to the skin. If we ignore all the pretty stuff, the skin is very simple:

<?xml version="1.0" encoding="utf-8"?>
<s:SparkSkin ...>
    ...
    <s:states>
        <s:State name="normal"/>
        <s:State name="prompting"/>
        <s:State name="disabled"/>
    </s:states>
 
    <s:RichEditableText id="textDisplay" ... />
    <s:Label id="promptDisplay" includeIn="prompting" ... />
</s:SparkSkin>

We add the prompting State to the list of states and also add the promptDisplay Label component. By using the standard inline state syntax, includeIn="prompting" our Label is shown only in the prompting state.

A Clearable TextInput

The second piece of SuperTextInput functionality is the clear button. The clear button appears when the TextInput has a value, and when clicked, it clears that value (which re-displays the prompt). Again, there are two pieces of information the need to be communicated to the skin to create the clear button functionality: the button itself and it’s visibility. In this case, since the visibility is so simple (on if TextInput has a value, otherwise off), we’ll just punt and manage it directly in the component. Therefore, the only a Button SkinPart for the clear button will be pushed to the skin.

Here’s a functioning ClearableTextInput custom component (which is simply the clear button code lifted from SuperTextInput.as):

package components {
    import flash.events.Event;
    import flash.events.MouseEvent;
    import mx.events.FlexEvent;
    import spark.components.Button;
    import spark.components.TextInput;
    import spark.events.TextOperationEvent;
 
    public class ClearableTextInput extends TextInput {
 
        [SkinPart(required="false")]
        public var clearButton:Button;
 
        public function ClearableTextInput() {
            super();
 
            //watch for programmatic changes to text property
            this.addEventListener(FlexEvent.VALUE_COMMIT, textChangedHandler, false, 0, true);
 
            //watch for user changes (aka typing) to text property
            this.addEventListener(TextOperationEvent.CHANGE, textChangedHandler, false, 0, true);
        }
 
        private function textChangedHandler(e:Event):void {
            if (clearButton) {
                clearButton.visible = (text.length > 0);
            }
        }
 
        private function clearClick(e:MouseEvent):void {
            text = '';
        }
 
        override protected function partAdded(partName:String, instance:Object):void {
            super.partAdded(partName, instance);
 
            if (instance == clearButton) {
                clearButton.addEventListener(MouseEvent.CLICK, clearClick);
                clearButton.visible = (text != null && text.length > 0);
            }
        }
 
        override protected function partRemoved(partName:String, instance:Object):void {
            super.partRemoved(partName, instance);
 
            if (instance == clearButton) {
                clearButton.removeEventListener(MouseEvent.CLICK, clearClick);
            }
        }
    }
}

After the PromptingTextInput, the ClearableTextInput is a little more straightforward. First, we have the clearButton SkinPart and it’s clearClick() event handler. Wiring the handler function to the button is done in the partAdded() override, and un-wiring in the partRemoved() override. Next, button visibility is managed by watching for both programmatic text change events and user text change events. The handler, textChangedHandler(), sets the button as visible when the control has text in it.

As I mentioned above, I decided against pushing the clearButton‘s visibility down to the skin via a SkinState, and instead chose to manage it inside the component by setting clearButton.visible directly. I tend to favor the SkinState method when more than one thing needs to change in the skin or if I need advanced visuals (like transitions). If I need to do just one thing and I don’t care about visuals, I’ll do it inside the component. The two examples here aren’t the best to illustrate the two options, but that’s my general thought process when building a custom component and custom skin.

A skin for ClearingTextInput is super trivial. Again, ignoring all the pretty stuff, the skin is:

<?xml version="1.0" encoding="utf-8"?>
<s:SparkSkin ...>
    ...
    <s:states>
        <s:State name="normal"/>
        <s:State name="disabled"/>
    </s:states>
 
    <s:RichEditableText id="textDisplay" ... />
    <s:Button id="clearButton" ... />
</s:SparkSkin>

Just add the clearButton Button and position it.

Fusion, Glorious Fusion

The fusion process of creating SuperTextInput from PromptingTextInput and ClearableTextInput is nothing more than copy and paste. SuperTextInput has lots of uses, but my favorite is to use it to capture text input to filter a list. It also works great as a search box, or in any smart form UI. Enjoy.

Here’s the finished product showing all three custom components skinned and ready for action (view source enabled):

Files

• SuperTextInput (download)

The Flex 3 Way

To give a concrete example, I’ll build a blog layout (yes, another blog layout) with a header, footer, sidebar, and main content areas. But before we get started, let’s review the old Flex 3 way:

<mx:HBox id="header">
    <mx:Image source="@Embed('assets/logo.png')" />
</mx:HBox>
 
<mx:Canvas id="body" width="800">
    <mx:Text text="main content" width="600" />
 
    <mx:VBox id="sidebar" x="600" width="200">
        <mx:Text text="Sidebar" />
        <mx:Text text="sidebar content" width="100%" />
    </mx:VBox>
</mx:Canvas>
 
<mx:VBox id="footer">
    <mx:Text text="2010 saturnboy" styleName="footer" />
</mx:VBox>

The above code comes from a previous post, Designing in Flex 3, but has been modified to make sense here. You’ve got you basic blog design: a box for the header, footer, and body, where body is subsequently is divided into a main content area and a sidebar.

The 3-in-4 Way, aka The Wrong Way

The unfortunate next step in a Flex developer’s evolution is what I like to call the Flex 3-in-4 way. This is a the way of neanderthals, which is to say, it is an evolutionary dead end. If you ever have the bad luck to see 3-in-4 code, you can be sure you are dealing with a novice Flex 4 developer. In general, the 3-in-4 way consists of making the simple transcription: Canvas → Group, HBox → HGroup, VBox → VGroup. But the most damning tipoff of a 3-in-4 developer is the assertion that one is now a Flex 4 developer and the learning curve wasn’t all that bad. While I do think Flex 4 is more of an evolutionary release than a revolutionary release, it’s different enough. And it is particularly different on the design side of the framework, how it handles skins, layout, etc.

If we just transcribe the above example, we get some classic 3-in-4 code:

<s:HGroup id="header">
    <s:Label text="Multi Content Area Example" styleName="header" />
</s:HGroup>
 
<s:Group id="body" width="800">
    <s:Label text="main content" width="600" />
 
    <s:VGroup x="600" width="200" styleName="sidebarBox">
        <s:Label text="Sidebar" styleName="title" />
        <s:Label text="sidebar content" styleName="sidebar" />
    </s:VGroup>
</s:Group>
 
<s:VGroup id="footer">
    <s:Label text="2010 saturnboy" styleName="footer" />
</s:VGroup>

*Barf*, please not do this. This code has all the same issues as the Flex 3 code in the first example, and moreover it is a slap in the face of The Flex 4 Way and all of its improvements.

The Flex 4 Way

Yes, there is a Flex 4 Way and it looks like this.

First, we rewrite the main app using a custom container. Ignoring the specifics of the custom container for a moment, here is the re-written main app (minus some clutter):

<containers:headerContent>
    <s:Label text="Multi Content Area Example" styleName="header" />
</containers:headerContent>
 
<containers:sidebarContent>
    <s:RichText left="0" right="0" styleName="sidebar">
        <s:content>
            <s:p fontSize="20">Sidebar</s:p>
            <s:p>sidebar content</s:p>
        </s:content>
    </s:RichText>
</containers:sidebarContent>
 
<containers:footerContent>
    <s:Label text="2010 saturnboy" styleName="footer" />
</containers:footerContent>
 
<s:RichText left="0" right="0">
    <s:content>
        <s:p fontSize="30">Content</s:p>
        <s:p>main content</s:p>
    </s:content>
</s:RichText>

As you can see, the main app is now a nice set of semantic buckets, one for each of the content areas. Header stuff goes in the headerContent bucket, footer stuff goes in the footerContent bucket, etc.

Building a Multi Content Area Container

Second, we need to create a custom container with the nice set of semantic buckets used in the above code. This is achieved by following a straightforward formula:

1. Extend SkinnableContainer – Extend SkinnableContainer or some child class. In our sample app, our custom container extends Application (which extends SkinnableContainer).
2. Add Buckets – add some content buckets (in the form of xxxContent) as Arrays. These become the MXML tags used to bucket components together. Each content bucket has a public getter, but most importantly a public setter that accepts an incoming Array of IVisualElements and uses the magical mxmlContent property to assign it to the associated SkinPart.
3. Add SkinParts – add some matching SkinParts (in the form of xxxGroup) as spark Groups. There are used in the custom skin to display the content. Also, I usually set required="false" to make everything optional.
4. Add partAdded() & partRemoved() – override the new Flex 4 skinning lifecycle methods to wire the incoming content to the outgoing SkinPart.

The custom component code is actually easier to follow then the description. Here is a custom container with only one additional content bucket, sidebarContent, and its matching SkinPart, sidebarGroup:

package containers {
    import spark.components.Group;
    import spark.components.Application;
 
    public class MainApp extends Application {
        [SkinPart(required="false")]
        public var sidebarGroup:Group;
 
        private var _sidebarContent:Array = [];
 
        public function MainApp() {
            super();
        }
 
        [ArrayElementType("mx.core.IVisualElement")]
        public function get sidebarContent():Array {
            return _sidebarContent;
        }
        public function set sidebarContent(value:Array):void {
            _sidebarContent = value;
            if (sidebarGroup) {
                sidebarGroup.mxmlContent = value;
            }
        }
 
        override protected function partAdded(partName:String, instance:Object):void {
            super.partAdded(partName, instance);
 
            if (instance == sidebarGroup) {
                sidebarGroup.mxmlContent = _sidebarContent;
            }
        }
 
        override protected function partRemoved(partName:String, instance:Object):void {
            super.partRemoved(partName, instance);
 
            if (instance == sidebarGroup) {
                sidebarGroup.mxmlContent = null;
            }
        }
    }
}

Following the four steps: we extend Application, have a sidebarContent bucket and its associated sidebarGroup SkinPart, and override partAdded() and partRemoved() to wire everything together.

Skinning a Multi Content Area Container

Skinning in Flex 4 is awesome, and like everyone says, it’s easily one of the best new features in the framework. While I find the skinning process fairly straightforward, I would never call it trivial, mostly due to the depth and flexibility of the skinning system.

We need a custom skin for our custom multi content area component. This is probably the 10% case for skinning, but it’s also the coolest. In my experience, an average Flex 4 app has many Button skins (like 10 or even 20), a few default component skins (skins for List, DropDownList, TextInput, etc.), and maybe only two or three skins for custom components.

The skin itself is nothing special. To display our custom component’s SkinParts, we simply include a Group with the matching id attribute. For example, our skin will include a <s:Group id="sidebarGroup" /> to display the sidebarGroup SkinPart. Just rinse, wash, repeat, to add all of our custom content areas in the container to the skin.

Here is a trivial skin:

<s:Skin ... >
    <fx:Metadata>
        [HostComponent("containers.MainApp")]
    </fx:Metadata> 
 
    <s:states>
        <s:State name="normal" />
        <s:State name="disabled" />
    </s:states>
 
    <s:VGroup left="40" right="40" top="40" bottom="40" gap="20">
        <s:Group id="headerGroup" width="100%" />
        <s:Group id="contentGroup" width="100%" />
        <s:Group id="sidebarGroup" width="100%" />
        <s:Group id="footerGroup" width="100%" />
    </s:VGroup>
</s:Skin>

In this trivial skin, we just shove all the content groups (including SkinnableContainer‘s default Group, contentGroup) into a VGroup. Also note, we correctly set HostComponent to our custom container. If you are thinking, "Hey, this skin looks similar to the Flex 3 and 3-in-4 example code, just minus the content" that’s exactly the point.

Lastly, we wire out skin to our custom component via CSS:

containers|MainApp {
    skinClass:ClassReference('skins.TrivialAppSkin');
}

Using skinClass to wire a skin to a component is so 2009. The sample app has its CSS inline, but in any real app I’ll always put this in an external file.

Conclusion

After this, there’s really not much more to say. You can certainly create a more complicated arrangement of the multiple content areas by making a more complicated skin. I’ve done exactly this in the final sample, which includes three different skins and a skin switcher (click 1, 2, or 3 to switch skins).

» view MultiConentArea sample (view source enabled)

Files

• MultiContentArea (download)

The Drawer component is a vanilla container (it actually extends SkinnableContainer), so it will happily take any spark component for its children. Before I dive into my implementation, let’s check out the finished drawer component in action (view source enabled):

Just click on the handle to open and close the drawer.

Extending SkinnableContainer

The Drawer component itself, is just pure AS3, but the demo above uses a few MXML skins to achieve the desired look-and-feel. This is a pretty standard pattern that I see during Flex 4 development, so expect it when you write your own custom components.

We’ll review the component implementation in two steps. First, we focus on the skin state management aspect of the drawer. Here’s the relevant code (taken from Drawer.as):

[SkinState("opened")]
public class Drawer extends SkinnableContainer {
    private var _opened:Boolean = false;
 
    public function get opened():Boolean {
        return _opened;
    }
 
    public function set opened(value:Boolean):void {
        if (_opened != value) {
            _opened = value;
            invalidateSkinState();
        }
    }
 
    override protected function getCurrentSkinState():String {
        return (opened ? 'opened' : super.getCurrentSkinState());
    }
    ...
}

The Drawer component can either be closed (the default) or opened. To model theses states, we use the normal state from the superclass to represent the closed drawer, and add a new opened SkinState to represent the opened drawer. We just expose a simple opened boolean property with a custom getter and setter, and then override the getCurrentSkinState() method. It’s important to remember the states we are talking about are skin states, and not component states (see Flex 4 Component States vs. Skin States for the difference).

Second, we focus on the action of opening and closing the drawer. Here’s the relevant code (taken from Drawer.as):

public class Drawer extends SkinnableContainer {
    ...
    [SkinPart(required="false")]
    public var openButton:Button;
 
    private function clickHandler(event:MouseEvent):void {
        opened = !opened;
    }
 
    override protected function partAdded(partName:String, instance:Object):void {
        super.partAdded(partName, instance);
        if (instance == openButton) {
            openButton.addEventListener(MouseEvent.CLICK, clickHandler);
        }
    }
 
    override protected function partRemoved(partName:String, instance:Object):void {
        super.partRemoved(partName, instance);
        if (instance == openButton) {
            openButton.removeEventListener(MouseEvent.CLICK, clickHandler);
        }
    }
}

The Drawer component includes a simple spark button, as an optional SkinPart, that is used to initiate the state change. The partAdded() and partRemoved() methods are overridden to manage and adding and removing of the button’s click event handler. And lastly, the clickHandler() method flips between skin states by toggling the opened boolean property.

Usage

Using the Drawer is the same as any container. In MXML, just put any child components you want between the container’s open and close tags:

<containers:Drawer ... skinClass="skins.DrawerSkin">
    <!-- components go here -->
</containers:Drawer>

Here we also apply the DrawerSkin to our container.

Skins

The DrawerSkin is responsible for creating the desired look-and-feel and generally making the Drawer component look cool. Here are the interesting parts of the skin:

<s:Skin ...>
 
    <fx:Metadata>
        [HostComponent("containers.Drawer")]
    </fx:Metadata>
 
    <s:states>
        <s:State name="normal" />
        <s:State name="opened" />
        <s:State name="disabled" />
    </s:states>
 
   ...
 
    <s:Button id="openButton" ...
            skinClass="skins.DrawerOpenButtonSkin"
            skinClass.opened="skins.DrawerCloseButtonSkin" />
 
    <s:Group id="contentGroup" ... includeIn="opened" />
</s:Skin>

The DrawerSkin has three skin states, normal and disabled are inherited from SkinnableContainer, but opened is our custom skin state. The skin also includes the optional openButton SkinPart, which itself uses two custom buttons skins, one for the open drawer and one for the closed drawer. Lastly, note that the container’s content is only displayed when the skin is in the opened state via the newfangled inline state syntax: includeIn="opened".

Files

• Drawer (download)