Dynamic loading of CSS files is not supported in Flex. CSS in Flex is processed on the server side during MXML compilation rather than on the client side at runtime.

There is a trick though: a CSS file can be compiled into a separate SWF file and loaded dynamically into the application using the Loader component. More information on this topic can be found on Manish Jethani's blog:

http://www.livejournal.com/users/mannu/286686.html

Flex 1.5

Unfortunately double-click is not supported by default. If you wish to add this functionality to say a List or DataGrid component, you will have to add the following AS2 code to your application:

// used to detect a double-click
var someTimestamp:Number;

...

/**
 * Double-click handler for some DataGrid component.
 */
public function doubleClickHandler( evt:Object ):Void {
	var now = getTimer();

	// we got a double-click
	if( ( now - someTimestamp ) < 500 ) {
		// do something here ...
	}

	someTimestamp = now;
}

Flex 2.0

The MouseEvent supports a Double Click event. Eg:

 addEventListener(MouseEvent.DOUBLE_CLICK, doubleClickHandler);

The whitelist is a security feature in Flex that requires you to explicitly define which URLs a data service call can access.

You set this by editing the file: ...\[flexroot]\WEB-INF\flex\flex-config.xml.

There are three sections, one each for WebService, HTTPService, and RemoteObject. Be sure you are editing in the correct section! Each has a subsection called , which contains nodes. To enable an url for access by a Flex dataService call, enter that url between the tags.

For development phase ONLY, you can allow global access with the wildcard rows. The flex-config file is heavily commented. Open it up and you will see more detailed instructions.

This is a focus issue with the Flash Player, usually when the UI changes "underneath" the mouse pointer, as in a ViewStack navigation where the buttons are in the same screen location.

A work around is to add this property to the button tag:

trackAsMenu="true"

Low-level methods like Array.push() or myArray[0] = "whatever" do not cause the dataProvider's modelChanged event to fire.

When working with a dataProvider, it is always best to use the dataProvider API.  In the above example, you might code: myDataProvider.addItem(myItemObject) to add an item or use editField() to programatically modify a value.  See "dataProvider" in the Flex API documentation:

http://livedocs.macromedia.com/flex/15/asdocs_en/index.html

Alternatively, you can call myDataProvider.modelChanged yourself, or re-assign the dataProvider to the control: myDataGrid.dataProvider = myDataProvider;

Select a node in your Tree.  In ActionScript, you can reference this node by saying:
myTree.selectedNode;

To access the attributes of the node use the tree DataProvider API.  These methods will work for any format dataProvider item, which might be an object or an array or an xml node.

For example,
myTree.selectedNode.attributes.myAttribute MIGHT work,

but :
myTree.selectedNode.getProperty("myAttribute"); is far more reliable.

See dataProvider and treeDataProvider in the on-line API documentation:
http://livedocs.macromedia.com/flex/15/asdocs_en/index.html

Flex 1.5:

This is technically possible. 

However, the Flex license requires the presence of a Flex server, and SWFs compiled using the Developer version of Flex will expire in 1 day.  Review the license carefully.

If you have a special business case, contact your Macromedia sales rep, as they are often willing to discuss special agreements.

Flex 2.0:

This is the norm. You use the SDK or FlexBuilder IDE to compile your Flex Clients; they'll be out of the box ready to work with HTTPService's, WebServices, and Coldfusion RemoteObjects. Optionally the new Flex Data Services can be used to hook into Java POJO's, and utilize data paging, messaging/rtmp, etc...

Tracy Spratt has put together a very simple example that you can download here: http://www.cflex.net/ChannelFiles/1/popupexample2.zip. Details regarding how this works can be read via http://www.cflex.net/showfiledetails.cfm?objectID=197.

Generally speaking, binding needs type information to set up its change detection functionality, and anything that hides this info can cause this problem. 

• Don't use mx.core.application.application.myVariable in binding. 
• If you are passing a reference to some component into another component via public properties, type the property variable definition as specifically as possible.
• When using "dot.down" notation to specify a property in an object or model, cast it to a type: text="{String(myObject.whatever.firstName)}"

With the current Flex 1.5 component set, there is no Rich Text Editor unfortunately. There are some limitations in the current Flash Player that make such an editor difficult though there are implementations out there people have used. Macromedia has heard many requests for a Rich Text Editor and has indicated there might be better support in a future release.

There is a third party component called the FlashTextEditor that can be integrated.

Flex 2.0 will include the mx:RichTextEditor tag.

• RemoteObjects: Fastest. communicates with server side EJB's or POJOs using AMF, a binary, compressed format.
• HTTPService: uses HTTP protocol. Sources can be JSP, ASPx,.NET, files, any url that returns HTTP.
• WebService: Slowest. Uses SOAP protocol. Sources can be .Net, or any WebService.

There is a generic way to handle the asynchronous nature of data service calls called ACT (Asynchronous Call Token). Search for this in Developing Flex Apps doc for a full description, but here it is in a nutshell. This example uses HTTPService but will be similar for RemoteObject and WebService:

• First, create a function to handle the data return, like "onResult()"
• In the HTTPService tag, put this function name in the "result" property, passing in event.
• Invoke the call in script:

  //invokes the call to the HTTP data service 
  var oRequestCallbject = app.mxdsGetData.send(oRequest); //we will use this string value in the result handler. 
  //Yes, you CAN set this AFTER you invoke send() 
  oRequestCall.MyQueryId = "WhateverIWanttoUseToIdentifyThisCall" ;
  

• In the result handler, which will be called every time the data service call returns, you identify what the returned data contains like this:

  var callResponse = oEvent.call; //get the call object
  //gets the value of this property you set in the call 
  var sQueryId = callResponse.MyQueryId; //will be "WhateverIWanttoUseToIdentifyThisCall";
  trace(sQueryId); 
  

You can use this sQueryId value in a switch to do the correct processing. Alternatively, you can pass reference to a handler function directly.

In MXML:
{mx.utils.ArrayUtil.toArray(modelAccidents1.accidents.accident)}

And the inline format:
dataProvider={mx.utils.ArrayUtil.toArray(testSrv.result.result.error)}

And in ActionScript:
myControl.dataProvider = mx.utils.ArrayUtil.toArray(testSrv.result.result.error)

Flex 1.5: In order to improve FlexBuilder performance, it is best to disable the "Design View". This can only be done in FlexBuilder 1.5 and to do so, please follow these steps:

• Select "Preferences" under the "Edit" menu
• In the "General" section, remove the check mark next to "Enable MXML Design View"
• click on "OK"

Flex 2.0: The best thing you can do is disable the "Build Automatically" option.  Uncheck Project -> Build Automatically from the menu and you should see increased performance, especially during save operations.  Also, if you're not using a project make sure that you close it to free up memory.

Cairngorm: http://www.iterationtwo.com/open_source_cairngorm.html
FlexUnit: http://www.iterationtwo.com/open_source_flexunit.html
SynergyFLEX: http://www.mossyblog.com/archives/473.cfm (this link is for 1.0.0a)
ARP:  http://www.osflash.org/projects/arp/about
ASUnit: http://www.asunit.org