Programming Visual Basic for the Palm OS

Palm Buttons

The Palm’s buttons can also be captured and used to trigger debugging statements or functions. You might use this technique to asynchronously trace a program’s state information at various points in its execution. The most common Palm buttons are shown in Figure 10-2.

Figure 10-2. Common Palm buttons

The AppForge system library contains two functions that allow your program to register and release the keycode associated with a button.

RegisterKeyCode

Registers a keycode for a corresponding button

ReleaseKeyCode

Releases the keycode for a corresponding button

In addition to registering a keycode, you must set the active form’s KeyPreview property to True. Registered keys are then received as a Form_KeyDown event within your program. Example 10-3 shows how this works in code.

Example 10-3. Key registration and release

Public Const vchrHard1 = &H204               ' Leftmost hard key
Public Const vchrHard2 = &H205               ' Center-left hard key
Public Const vchrHard3 = &H206               ' Center-right hard key
Public Const vchrHard4 = &H207               ' Rightmost hard key

Private Sub Form_Load(  )

#If AFDEBUG Then
  RegisterKeyCode vchrHard1
  RegisterKeyCode vchrHard2
  RegisterKeyCode vchrHard3
  RegisterKeyCode vchrHard4
#End If

End Sub

Private Sub Form_Unload(Cancel As Integer)

#If AFDEBUG Then
   ReleaseKeyCode vchrHard1
   ReleaseKeyCode vchrHard2
   ReleaseKeyCode vchrHard3
   ReleaseKeyCode vchrHard4
#End If

End Sub

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