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This chapter is from the book

This chapter is from the book

The Relationship Between Messages and Events

Now that you know all the ins and outs of messages, recall that this chapter began by stating that VCL encapsulates many Windows messages in its event system. Delphi's event system is designed to be an easy interface into Windows messages. Many VCL events have a direct correlation with WM_XXX Windows messages. Table 3.3 shows some common VCL events and the Windows message responsible for each event.

Table 3.3 VCL Events and Corresponding Windows Messages

VCL Event

Windows Message

OnActivate

wm_Activate

OnClick

wm_XButtonDown

OnCreate

wm_Create

OnDblClick

wm_XButtonDblClick

OnKeyDown

wm_KeyDown

OnKeyPress

wm_Char

OnKeyUp

wm_KeyUp

OnPaint

WM_PAINT

OnResize

wm_Size

OnTimer

wm_Timer


Table 3.3 is a good rule-of-thumb reference when you're looking for events that correspond directly to messages.

TIP

Never write a message handler when you can use a predefined event to do the same thing. Because of the contract-free nature of events, you'll have fewer problems handling events than you will handling messages.

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