Using the Windows API Messaging Solution

Go Up to Using Messages

Components often need to respond to messages from the underlying operating system. The operating system informs the application of occurrences such as what the user does with the mouse and keyboard. Some controls also send messages, including for example the results from user actions such as selecting an item in a list box.

The VCL framework handles most of the common system messages already. It is possible, however, that you will need to write your own code for handling system messages or messages from VCL components.

Topics

• Understanding the Message-Handling System
  • What's in a Windows Message
  • Dispatching Messages
• Changing Message Handling
  • Overriding the Handler Method
    • Example of Overriding a Message Handler
  • Using Message Parameters
  • Trapping Messages
• Creating New Message Handlers
  • Defining Your Own Messages
    • Declaring a Message Identifier
    • Example of User-defined Messages
    • Declaring a Message-structure Type
    • Example of Message Structure
  • Declaring a New Message-handling Method
• Sending Messages
  • Broadcasting a Message to All Controls in a Form
  • Calling a Control's Message Handler Directly
  • Sending a Message Using the Windows Message Queue
  • Sending a Message That Does Not Execute Immediately
• The WndProc Method
• Handling Input Language Change Message