Friday, May 25, 2007

Bindows Wonderful dispose() Method

Almost anything useful you do with Bindows requires you to add components to other components. This is because you build visual components by creating parent child relationships.

So, if you wanted to build a custom dialog, MyDialog, you might start off with a BiComponent and use that as a container. Then add a BiToolBar to the BiComponent. Of course, you'll need toolbar buttons and menus so you add BiToolBarButtons and BiToolBarMenuButtons to the BiToolBar, etc.

When you're done, you add the BiComponent
container to the BiApplicationWindow.

We've effectively created a hierarchy where every component with the exception of the BiApplicationWindow is a child to another.

One reason why this is significant is when you dispose MyDialog.

All derivatives of BiComponents have access to a dispose() method. It may come directly from the component ( for example BiLabel has its own dispose method ) or directly from BiComponent or from BiObject ( read about dispose() ). As a front-end developer, you don't really care. You just have to remember to call it when you want to mark MyDialog for garbage collection.

So, calling dispose() traverses the children, removes their properties and sets them to null ( actually BiComponent's dispose() calls another method, disposeFields() which makes this happen, but it's all nicely abstracted for you ).

In cases where you only have a hierarchical relationship between your components, you don't need to implement dispose(). This is cool because all you do is call dispose() and the world is your oyster. Most of the time this is all you need to do.

However, if you create new objects in a custom component like MyDialog ( perhaps, we have an array of strings in MyDialog that we're using to temporarily store information ), then we'll need to implement our own dispose().

If we do, we need to make sure that we --

  • Call dispose() in the superclass ( for MyDialog, the superclass is BiComponent and can be done like this - ); this effectively propagates the disposal up the prototype chain
  • Call disposeFields(); disposeFields accepts a variable number of string arguments where each string is a property name; calling disposeFields removes ( i.e. deletes ) the property and disposes them if it's a Bindows objects; you can read about it here.
That's it. dispose() is pretty wonderful.
Have fun!

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