2 Replies Latest reply on Aug 16, 2006 4:54 PM by Matlus

    Question/Baffled about how binding works

      In an attempt to position my canvas in the center of the user's browser (no matter what the size). I ended up using the following code. The Application is set to a width and height of 100%.

      <mx:Canvas id="primaryCanvas" horizontalScrollPolicy="off" verticalScrollPolicy="off" x="{(parentDocument.width > backgroundImage.width)? parentDocument.width /2 - primaryCanvas.width / 2 : 0}" y="{(parentDocument.height > backgroundImage.height)? parentDocument.height /2 - primaryCanvas.height / 2 : 0}">

      In particular, focus on the x and y attributes. This works as I expect, as in, I get the result I want. However, I'm a bit baffeld about the under pinnings about how/why it works :)

      How does the canvas know to re-position itself each time the browser is re-sized?
      How would I make these bindings into a function so I don't have to have my "code" intermingled with the actual mxml parts? Or is this even possible?

      I have read various things on binding but still have the above outstanding questions.

        • 1. Re: Question/Baffled about how binding works
          inlineblue Level 1
          This is how it appears to work to me...

          The binding mechanism recognizes bindable variables in the expression you give it. If any of those variables change, the entire expression is re-evaluated. In this case, parentDocument.width is a bindable variable.

          One thing you can do is bind to a method call. The trick is to pass the method a bindable variable so that the binding mechanism calls your method whenever the variable changes. Something like:


          And getx() does the calculations and returns an int.
          • 2. Re: Question/Baffled about how binding works
            Matlus Level 1

            Thank you for you replies to my quires. You've been very helpful. I'll try this getx() method and see if it works.