title: Flex app with large number of UI objects == slow?
body: <p>I'm building my first Flex custom component, in Flex 3. It is a data table based on the 'Grid' container class, with a simple text Label in each cell. (DataGrid and AdvancedDataGrid were not appropriate starting points for my needs.) The component works quite well using smallish tables, but I tried stress-testing it using a larger table, and have been disappointed by the results.</p>
  
  <p>The component creation process has some slow spots, but those are in my power to optimize and aren't my primary concern. What worry me more are what appear to be limitations in the Flex framework itself.</p>
  
  <p>This 'large' sample table has a bit over 7000 cells in it. This is largish, but still 1-2 orders of magnitude less than the biggest I need to accommodate. In standard Grid structure, the main portion of the component consists of a Grid with 400 GridRows of 16 GridItems each, plus a few other smaller ancillary Grids.</p>
  
  <p>Once the table renders, I find the following:</p>
  
  <ul>
  <li>Mouse-related events are slow to fire. Specifically, I have rollOver/rollOut event handlers registered on each table cell, to let me highlight the cell under the pointer. On a small table, I could move the mouse over the table very quickly, and the highlighting would follow the pointer in real-time. With the larger table, the highlighting is very jerky, changing only about twice per second, skipping over many cells.</li>
  <li>If I place the mouse cursor over the component and leave it there, my CPU is pegged (one processor core, anyway), and stays that way until I move off of the component, when it drops to idle. My component isn't doing anything at all at this point.</li>
  </ul>
  
  <p>It feels like Flex simply cannot scale to support component trees that are this large. I shudder to imagine how it would behave with 100,000 cells. Perhaps I'm pushing the Grid beyond its intended use, but having an object per table cell doesn't seem like an unreasonable model, and ~14,000 objects in the tree (a GridItem and a Label per cell) seems pretty modest.</p>
  
  <p>I have yet to get useful data out of the FlexBuilder profiler; I'm working on it. For now, my biggest questions are:</p>
  
  <ul>
  <li>Am I really pushing the limits of Flex with this modest test?</li>
  <li>Is my approach to this component completely off-base?</li>
  </ul>
  
  <p>I'm running this on Flash Player 9 under Firefox on WinXP.</p>