Wednesday, February 26, 2014

Widget's offsetsize is 0

I have had some problems with getting the size of widgets, I have been looking around for answers to my questions and have found a solution that I am not 100% happy with. My hope is that someone knows a better solution to my problem.

In my layout I am using a DockLayoutPanel, in the north I have a label that holds a title that will change depending on the place I am at in my application. In the center panel I have some scrollable content (Tables, trees, etc). I don't want the title and the content in the same panel because if I scroll down I will lose sight of the title, this is the reason for the separation. My problem occurs whenever I have a really long title that will need to wrap in order to fit on the screen. With a DockLayoutPanel you have to give a fixed height to the north panel, in my case I need this height to increase should the title wrap to the second line. What I want to be able to do is in the method that I set the text for the title label, I need to calculate the height of the label, and set the north panel to that height so that the entire title will be visible.

Now that sounds simple enough, but if you just set the text of the label and then call getOffsetHeight() it will return 0. What I learned is that you have to wait until the widget is rendered before getting the height. In the past I used a deferred command like this:

Scheduler.get().scheduleDeferred(new ScheduledCommand() {	  	@Override  	public void execute() {  		// TODO Auto-generated method stub		  	}  });

A deferred command is executed after the browser event loop returns. This has worked for me every time in the past until now. For some reason the command was firing before the label was displayed. If someone could enlighten me as to why this doesn't work I would appreciate it.

What I found that works, although I am not 100% happy with it is scheduling a command on a fixed delay like this:

Scheduler.get().scheduleFixedDelay(new Scheduler.RepeatingCommand() {      @Override      public boolean execute() {          if (northPanel.getOffsetHeight() != 0) {              centerDock.setWidgetSize(northPanel, northPanel.getOffsetHeight());              return false;          } else {              return true;          }      }  }, 100);

This schedules a repeating command that is scheduled with a constant delay. That is, the next invocation of the command will be scheduled for 100 milliseconds after the last invocation completes in this example.

So I just had the thing run this command until the offset height gave me a positive number, then it gets stopped by returning false in the execute method.

While this works it seems a bit sloppy, if anyone knows a better solution I would be happy to hear about it.



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