R – flex3 type casting

actionscript-3apache-flexflex3

Does anyone know the real difference between the two ways of type casting in Flex 3?

var myObject1:MyObject = variable as MyObject;
var myObject2:MyObject = MyObject(variable);

I prefer to use the second method because it will throw an Error when type cast fails, whereas the first method will just return null. But are there any other differences? Perhaps any advantages to using the first method?

Best Answer

The second type of casting has different behaviour for top level(http://livedocs.adobe.com/flex/2/langref/) types, e.g. Array(obj) does not cast in the straightforward way you describe; it creates a new Array if possible from obj, even if obj is an Array.

I'm sure the times this would cause unexpected behaviour would be rare but I always use "as" for this reason. It means if I do

int(str)

I know it's a cast in the "attempt to convert" sense of the word not in the "I promise it is" sense.

ref: got some confirmation on this from http://raghuonflex.wordpress.com/2007/07/27/casting-vs-the-as-operator/

Related Solutions

R – Flex3 Canvas, ScrollBar

The problem you've discovered is that plain UIComponent does not report a width or height value to its parent (because it simply doesn't know what that value should be!).

If you must work with simple Sprites and other primitive display objects in Flex, I would recommend creating a subclass of UIComponent with an override of the measure() function. In there, set the measuredWidth and measuredHeight properties to the size of the UIComponent's children.

This is a quick (and untested) solution you might want to try (in your UIComponent subclass that will replace the plain UIComponent):

override protected function measure():void
{
    super.measure();

    for(var i:int = 0; i < this.numChildren; i++)
    {
        var child:DisplayObject = this.getChildAt(i);
        this.measuredWidth = Math.max(this.measuredWidth, child.x + child.width);
        this.measuredHeight = Math.max(this.measuredHeight, child.y + child.height);
    }
}

Personally, whenever possible, I try to make all content proper subclasses of UIComponent rather than creating hacks like this to make Sprite or other non-UIComponent types work inside Flex's containers. However, your approach seems to be very common, so hopefully this will be useful to you and others.

R – Flex 3.2 casting problem

FYI, a type loaded into a child ApplicationDomain can be cast to a type (that it extends/implements) in the parent ApplicationDomain.

Eg.

loader.applicationDomain = ApplicationDomain.currentDomain; // parent domain
loader.applicationDomain = new ApplicationDomain(ApplicationDomain.currentDomain); // child domain
loader.applicationDomain = new ApplicationDomain(); // new domain

Best Answer

Related Solutions

R – Flex3 Canvas, ScrollBar

R – Flex 3.2 casting problem

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