Question

I was told that there is an increase in performance when using Canvas versus HBox or VBox when laying out out the position of children. As a result, a number of our components have been converted over to using Canvas. However, now there is code being added to calculate the x and y positioning of some of the child elements based off of the width and height of other children. Is it worth using a Canvas to increase performance if code needs to be added to determine the coordinates/positions of the children? Is there a better method or technique available that should be practiced other than just minimizing the number of ui components added and specifying positioning absolutely?

Answer 1

There are a number of middle-of-the-road techniques, one of which is to use rendering-type components, such as TileGrid or ItemRenderers, if your layout fits a certain formula. If you’re using forms, try using the Form layout component instead of using a custom layout.

If you do need to use the layout engine in Flex, the way to optimize your usage is to remember that certain techniques are used by the framework in increasing performance load, loosely following the below list, the last being the most performance intensive:

1. absolute positioning (<Canvas>)
2. relative positioning (<VBox>)
3. constraint-based positioning (right=0)
4. advanced constraint-based positioning (<constraintColumns>)

Using relative positioning is usually not that performance intensive. If you are finding that it is, it could be that you’re using too many nested containers. Look at your layout architecture and try to find out ways in which your objects may be “over-laid out”, and simplify them. A good tool for this is FlexSpy, which lets you introspect object layout at runtime.

Another common performance bottleneck is that your application is attempting to do some number-crunching at the exact same time that your GUI is attempting to respond to user interaction. Although no green threading frameworks exist at the moment which enable you to run UI and logic in separate ‘threads’, you can use a good architectural framework such as Cairngorm or Mate (there are many) which uses Commands instead of straight up methods, so that functionality execution which may take up processing cycles waits until the UI has finished responding to the user.