The Joy of Flex

(One in a series of random, daily, useful Flex tips.)

If you have a Label or another component that uses a Label or derives from a Label, you may run into situations where you need to update the Label’s text property and then immediately use its textWidth property in a calculation. Normally, the textWidth property will not be updated until later when the Label’s commitProperties() runs. But if you need to use its textWidth property immediately, you can call validateNow() on the Label. That will cause the Label’s commitProperties() to run immediately, after which you can get the correct value of textWidth.

In the example below, I’m using a Label to display the title of a document. When the underlying data structure changes, I need to update the title, then truncate its width to the width of the column it’s being displayed in. Here’s the commitProperties() of the UIComponent I’m using to do the display, which has a Label as a member variable:

override protected function commitProperties():void
    {
        super.commitProperties();
        if (_documentListInfoChanged)
        {
        	_label.text = _documentListInfo.title;
        	_label.validateNow();
        	_label.width = Math.min(_label.textWidth + UITextField.TEXT_WIDTH_PADDING*2, maxTitleWidth);
        	_documentListInfoChanged = false;
         }
    }

By the way, calling validateNow() can be useful in many situations; this is just one specific and common case.

Technorati Tags: Flex, Flex Tip of the Day