Scrolling Large Blocks of Text with Flex for Mobile

I was recently asked by a friend and former colleague about the best way to get text within a s:Label to behave and scroll properly, especially in the Flex mobile SDK. In particular, having a large block of text wrap correctly and scroll only in the vertical direction. By default if you don’t set a size on the label, the behavior of the Flex framework is that the views containing the label will resize, and the text will be displayed as entered (without word wrap or truncation). This may cause some layout issues and confusion as to “what the heck is going on with my text”.

I’ve found that the best way to achieve the desired behavior is to set a maxWidth on the label to force proper word wrapping, and then wrap the label in a s:Scroller to have it scroll properly. I chose to set a maxWidth to allow the label to determine it’s own size, and only to wrap if it needs to. An easy shortcut for proper wrapping is to bind the maxWidth of the label to the width of the scroller component. Also, DO NOT set a static height or a max height. This will cause the text within the label to be truncated, and it will not scroll at all if the static height is less than the height of the scroller. I’ve also noticed that setting cacheAsBitmap=true on the label also helps scroll performance in some circumstances, but this is not required.

Check out a video showing the scroll behavior of a large text block using this approach:

Below is the code that makes it work, which follows the method described above:

[as3]<s:Scroller height="100%" width="100%" id="scroller1">
<s:Label id="labelInstance"
maxWidth="{ scroller1.width }"
color="#FF0000" fontSize="32">
<s:text>Bacon ipsum dolor sit amet sint cow irure et magna, meatball aliquip qui. Tempor turkey capicola, eiusmod sed nisi dolore. Pig nisi rump boudin in culpa chuck. In ex sausage filet mignon shankle ut. Flank ball tip cillum aute. Nulla frankfurter culpa, elit et esse aute pork salami. Laborum mollit short ribs, in meatloaf eu irure dolor consectetur elit strip steak.

{note: text has been truncated to emphasize actual code, not the random text}

This post is also “powered by bacon”… yes, bacon.

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