ADM Blog

Create professional Flex components

Flex Builder has a great way to organize its components in tree mode, which is very a good way to organize things and make things clear to any user who are coming to Flex world.

By default, every component you create that is not part of default Flex components you will have placed in the [Custom] directory of Flex Components view in your Flex/Flash Builder, and no matter what properties you add to them, they will never be visible in the Flex Properties standard view.

But what if you want to customize that and create a component that have them all like flex components do? Well, it's not that hard so let's do that.

Create the Component

First, you have to create a new Flex Library Project. Do this by going to File->New and choose Flex Library Project. Give it a name, a location, choose whatever Flex SDK you wish to build this for and then click finish.

Now you have a blank library project in which you can create whatever components you want.
Is important to use packages correctly and namespaces and not just drop the component in the [src] folder (you'll see later why). First create a package (eg. com.adm.component) in which you can add your custom component.

package com.adm.component
      import mx.containers.Canvas;
      public class mycomponent extends Canvas

Okay, now let's create some methods to have something going. We'll make this component be a big button with a method to enable the button and one to change it's caption. We'll use setters and getter's for those properties because some other actions might be required when changing them. So:

package com.adm.component
     import mx.containers.Canvas;
     import mx.controls.Button;
      public class mycomponent extends Canvas
            private var _title : String = 'Title';
            private var _active : Boolean = true;
            private var btn : Button = new Button();
            public function CustomComponent()
                      this.btn.width = 100;
                      this.btn.height = 100;
                      this.btn.label = this.label;
            public function set title(val : String) : void
                      this._title = val;
                      this.btn.label = val;
            public function get title() : String
                     return this._title;
            public function set active(val : Boolean) : void
                     this._active = val;
                     this.btn.enabled= val;
            public function get active() : Boolean
                    return this._active;

So, if you now build your project, a .swc file will be generated in your [bin] folder, which you can add in other projects and use. But now, the component will be placed in the [Custom] directory in the Components View and not the one you want. We'll do that a bit later now let's just....

Give it an icon

This is really simple. All you have to do is get a nice looking .png icon (16x16 pixels preferably) and place it next to your component. Then, use the IconFile metadata tag to link it to your component.

public class mycomponent extends Canvas
       private var _title : String = 'Title';

Inspectable properties

If you have extra information about the property that will help code hints or the Property Inspector (such as enumeration values or that a String is actually a file path) then also add [Inspectable] metadata with that extra info. For our methods we have:

       [Inspectable(category="General", type="String", defaultValue="")]
       public function set title(val : String) : void
       [Inspectable(category="General", type="Boolean", defaultValue="true", enumeration="true,false")]
       public function set active(val : Boolean) : void

This will also help a lot when we'll add this properties in the Flex Properties panel. For more informations about the [Inspectable] metadata tag visit

Create custom component folder

So, if you want to build a professional component, you can't leave Flex add your component in the default [Custom] directory in the Components tree. So, in order to create your own folder, we must use few tricks.

First of all, you need two .xml files to describe the structure you want flex to use and overide it's default behavior.
The first file is the manifest.xml which describes the components in the package and their namespaces. In our case we'll have:

< ?xml version="1.0"?>
    <component id="mycomponent" class="org.adm.component.mycomponent"/>

Second, we need another xml to describe the way the designer will interpret all this.

< ?xml version="1.0" ?>
		<namespace prefix="adm" uri="" />
		<category id="Test" label="Test Panel" defaultExpand="true" />
		<component name="mycomponent" namespace="adm" category="Test" displayName="Rename Me" />

In the design.xml, you can specify the namespaces you used for the components, in this case adm will point to components in the org.adm folder.

Categories tag describes the folders you want added in the Components panel. Each category must have an id which you'll use to tell components where they should reside, a label for the category to stand as the directory name in the Components panel. defaultExpand is an optional parameter which if set to true, the folder will be showed expanded by default.

In the components tag, you specify which component goes in what category and under what title. The name parameter must match the id of a component listed in the manifest.xml. All the other parameters are pretty self explanatory.

Next, you have to include this two files in .swc package. To do that, follow the steps:

* Right Click at your project and select Properties
* In the left choose Flex Library Build Path
* Select the assets tab and mark to include manifest.xml and design.xml files
* Now select the Flex Library Compiler and include your namespace URL (in this case
* Include the manifest file .xml you've created
* Click apply and ok to finish


After this, you should end up with something like this


Add properties to the Flex Properties view

As I said before, no matter what properties you add to your component, they will never be visible in the Flex Properties standard view, only in the category view and that only if you use the [Inspectable] metadata tag. But few more lines in the design.xml file should take care of that.

	<component name="mycomponent" namespace="adm" category="Test" displayName="Rename Me">
			<textfield id="title" name="Component Title:" />
			<combo id="active" name="Active:" />
		<defaultattribute name="active" value="true" />

The id of the mxmlProperties tag should be the function/variable names from your component you want to edit. You can also define default values for those properties using the defaultAttribute tag below. Here we've only used the textfield and the combo type but there are few more you can use.

<textfiled id="propertyOrStyle" name="Label:" [multiline="false"] />
<combo id="propertyOrStyle" name="Label:" />
<colorpicker id="propertyOrStyle" name="Label:" />
<filepicker id="propertyOrStyle" name="Label:" [wrapInEmbed="false"] />
<slider id="propertyOrStyle" name="Label:" min="0" max="10" increment="1" />

For combo boxes, if you use it for a Boolean property, it will automatically be populated with [true,false] values but if want something else, the [Inspectable] metadata tag has the enumeration property where you can define the properties from this combo.


Another thing you must do in order to apply the values as soon as you change them from the properties view, is to set the functions/variables as [Bindable].

    [Inspectable(category="General", type="String", defaultValue="")]
    public function set title(val : String) : void
    [Inspectable(category="General", type="Boolean", defaultValue="true", enumeration="true,false")]
    public function set active(val : Boolean) : void

One more thing

Now, compiling this will give you a 300 something KB .swc file which is a bit large to distribute. The user will use this component inside a flex component so embedding all the libraries and SDK inside your .swc is useless. So the next step is to go to Properties->Flex Library Build Path->Library path tab, expand the build path library try and edit everything inside the SDK tree on Link Type and choose External


Now the swc component only have 4KB. Big cut down, eh ?


If this is to much trouble for you or you've missed something, I've attached the sources for this tutorial here. You can import this skeleton rename the package, namespace and the component and start building on this. I hope it all made sense and....happy coding.

Comments (0) Trackbacks (3)
  1. Hi.

    I’ve followed your tutorial and my components are visible in toolbox.
    But… Properties defined in design.xml (+Inspectable tag) are not visible…

    And the property:

    public class TestPanel extends Panel
    [Inspectable(category=”General”, type=”Boolean”, defaultValue=”true”)]
    public var test:Boolean;

    What’s wrong?

  2. My design.xml file:

  3. @drzemik
    your xml didn’t show. Did you import the design.xml into the package as well ? I use Flex Plugin for Eclipse and sometimes it requires a restart to show. Don’t know why. Other than that…i don’t know what to tell you. It should work just fine. Maybe someting is mallformed in your design or manifest xml and that makes everything to fail. Try downloading the skeleton i made and modify/compile that. See if it works

  4. Hi,
    I’m a beginner in flex world.I need a vslider with two thumb.It will be such that if the screen color of the slider below the lower thumb will show red color,in between two thumb will show orange color and above upper thumb will show green color.
    Can you please help me?

  5. This tutorial does not work on Flash Builder 4. Do you have any idea how to implement such professional components on Flash Builder 4?


  6. removing from the xml files (+ fixing a few typos in the other code bits) seem to fix the compile problems in FB4.

    Otherwise, thanks for providing valuable insight into this :-)

  7. Hello,

    also exists checkbox:

    I’m trying to figure out how to get the button to generate the event, as in the case of click, change, etc..

    Can you tell me where I can reference about this?


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