Of course in the case of only three you can make it with radio buttons or checkboxes. Here after the question how to write such a component, the answer is:

Have you considered using radio buttons rather than a combo box?

Well, no, I’m not! I’d like to make it for such a big range. In my case it was more than 200 options, the case with radio buttons is not enough.

Finally I found a sample of a disabled list items on http://joshblog.net/ but yet again it was dealing with list, not a combo box. In my case the combo box has very important built in events and fires different kind of them in any special situation. That’s why I don’t think this sample could do the work.

Actually as it seems easy and usefull, almost nowhere there was such a component. In Adobe’s blogs I found interesting post http://blogs.adobe.com/aharui/2007/06/disabling_list_selection.html where the author describes how to make a list with that properties, and somewhere in the comments I found the component at last:

Make the .swf sample file with both symbols inside. In general it’s not that hard, just put this into your Flex application code:

[Embed(source="embed.swf", symbol="blue")]
private var blue:Class;

[Embed(source=”embed.swf, symbol=”red”)]
private var red:Class

Note that you’ve embed.swf file, which has to be in the same folder as the main .swf of the Flex app, and two symbols named red and blue for the sample. Be very careful when exporting the symbols from the .swf file. Do not forget to export them for actionscript.

If not exported like that, you’ll have trouble accessing them from the Flex app, and that’s the first problem you can have here.

The rest you have to do is to add this two lines of code in Flex:

var mc:MovieClip = new blue();
this.addChild(mc);

Note that the last line can have something else than ‘this’ if there’s other element to become parent of the imported MovieClip symbol. Here comes the first major problem. As www.airtightinteractive.com describes this technique does not work every time:

Sometimes when you do this you will get the following error:

TypeError: Error #1034: Type Coercion failed: cannot convert app_red@12510d1 to flash.display.MovieClip.

And the author shares his solution which is to add at least 2 keyframes for both movie clips, so that they can be visible as movie clips, if not they will remain visible only as Sprites.

I’m not as conviced this is the right answer of the question and the right solution. I’ve experimented with 1 or 2 keyframes and still have the same problem in Flex even if i cast the symbols as Sprite, not MovieClip:

var mc:MovieClip = new blue();
var mc:Sprite = new blue();

The solution from Adobes for me is not suficient, cause the movie clips we import (embed) does not serve as images but more like movie clips, which was the task from the beggining. And that’s what Adobe says:

Flex fully supports embedding Flash SWF files. You can embed different types of SWF files.
…
To reference a symbol, you specify the symbol parameter:
[Embed(source=’SWFFileName.swf’, symbol=’symbolName’)]

And again read carefully the note in the Adobe’s site:

Note: Flash defines three types of
symbols: Button, MovieClip, and Graphic. You can embed Button and
MovieClip symbols in a Flex application, but you cannot embed a Graphic symbol because it cannot be exported for ActionScript.

Here you can be sure that lack of exported for actionscript symbol is not accessible in Flex.

One of the main solutions is to embed the .swf as octet-stream:

[Embed(source="embed.swf", mimeType="application/octet-stream")]
private var blue:Class;

followed by:

var loader:Loader = new Loader()
loader.loadBytes(new blue());

And the key point of this will be the lines:

var red:Class = loader.contentLoaderInfo.applicationDomain.getDefinition("blue");
var mc:MovieClip = new red() as MovieClip;

I hope this can help

Demo is here:

Free download: here