Goal: Control visibility of controls in Flex DataGrid
Problem:Control of cells' visibility in Flex DataGrid turns out to be pretty tricky. If you simply use inline item renderer and bind it's visibility attribute to a data provider, it won't work.
Why:Fortunately, Flex is open source. So, we can dig a little deeper into why it does not work.
- Look at SDK 3.2.0: DataGridBase.as, line 1073 will show that Flex SDK will actually set the renderer to visible after set "data" property of the control.
- Also, the SDK may decide to hide the cell when it sees fit in various situations;
So, it is not desirable to control visibility directly. You are fighting with the SDK.
Solution(s):Solution 1: Use a container as item renderer, and embed your control inside the container.
Pros: Quick and easy to implement. An added benefit is that you can control cell layout;
Cons: As all the Flex text book will stress: using too many containers is very
BAD for performance! How bad? A 20X20 DataGrid may take at least 5 seconds to render!
Solution 2: Create custom control based on the control you want to use in the cell. And manage a new "forceHide" attribute, which will cooperate with the original "visible" attribute to decide a control's visibility. Please see the sample code below. Some details are missing, but you get the idea.
...
protected var _forceHide:Boolean = false;
/**
* visible by set method
*/
protected var _setVisible:Boolean = false;
/**
* If set, this control will not be visible. It will overwrite visible property.
* DataGrid tend to manipulate visible directly, we can only use
* this extra field to force hide control even if DataGrid decides
* that it can be shown.
*/
public function set forceHide(value:Boolean):void {
_forceHide = value;
setVisible(_setVisible);
invalidateProperties();
}
override public function setVisible(value:Boolean, noEvent:Boolean=false):void {
//save desired settings
_setVisible = value;
//forceHide can mask out change request
super.setVisible((!_forceHide) && value, noEvent);
}
...
Other Thoughts:How about "CallLater"? It turns out to be a bad idea. As stated before, Flex SDK may want to hide some controls. If your "CallLater" set a control's visible to true, when Flex SDK think it is invisible, you may see some ghost controls hanging around.
