Palm OS Programming, 2nd Edition

Form Object Events

Many of the form objects post specific kinds of events when they are tapped on or used. To use a particular type of form object, you’ll need to know what kinds of events that form object produces. Most of the form objects have similar structures:

• When the stylus is pressed on the object, it sends an enter event. In response to the enter event, the object responds appropriately while the stylus is pressed down. For example, a button highlights while the pen is within the button and unhighlights while it is outside the button, a scrollbar sends sclRepeatEvents while the user has a scroll arrow tapped, a list highlights the row the stylus is on and scrolls if necessary when the pen reaches the top or bottom of the list.

• When the stylus is released on the object, it sends a select event. If the stylus is released outside the object, it sends an exit event.

In all these events, the ID of the tapped form object is provided as part of the event, as well as a pointer to the form object itself. The ID allows you to distinguish between different instances, which generate the same types of events. For example, two buttons would both generate a ctlSelectEvent when tapped; you’d use the ID to distinguish between them.

Events Generated by a Successful Tap

Most often, you want to know only when an object has been successfully tapped; that is, the user lifts the stylus while still within the boundaries of the object. Table 9-1 contains the events that you will use most often. ...