Return to Sender(4)

OnClick event handler

File1

0

--

MainItem1

1

SpeedButtonClick

MainItem2

2

SpeedButtonClick

MainItem3

3

SpeedButtonClick

MainItem4

4

SpeedButtonClick

PopupItem1

1

SpeedButtonClick

PopupItem2

2

SpeedButtonClick

PopupItem3

3

SpeedButtonClick

PopupItem4

4

SpeedButtonClick

Figure 3: Setting the values of properties for the sample application''''s SpeedButton and MenuItem components.

Note that all the buttons and menu items have the same event handler, namely SpeedButtonClick (see Figure 4). This procedure is called from any of the SpeedButtons or menu items on the form (except MenuItem File1). It references two external procedures, PushButton and ReleaseButton.

procedure TForm1.SpeedButtonClick(Sender: TObject);

var

A : Integer;

begin

if Sender is TSpeedButton then

if TSpeedButton(Sender).Down then

PushButton(Sender)

else

ReleaseButton(Sender)

else

for A := 0 to ComponentCount-1 do

if Components[A] is TSpeedButton then

with Components[A] as TSpeedButton do

if Tag = TComponent(Sender).Tag then

begin

Down := not Down;

if Down then

PushButton(Self.Components[A])

else

ReleaseButton(Self.Components[A]);

end;

end;

Figure 4: Referencing PushButton and ReleaseButton with the SpeedButtonClick procedure.

SpeedButtonClick first determines which object sent the event. If it''''s a TSpeedButton, it simply passes that object to the PushButton or ReleaseButton procedure, depending on the button''''s state (up or down). These procedures simply allow convenient spots for the messages to be handled. In the following example, the Caption of Label1 is set to report the event that occurred:

procedure TForm1.PushButton(Sender: TObject);

begin

Label1.Caption :=

TComponent(Sender).Name '''' was clicked.'''';

end;

procedure TForm1.ReleaseButton(Sender: TObject);

begin

Label1.Caption :=

TComponent(Sender).Name '''' was released.'''';

end;

If the Sender of the event is not one of the buttons, we must determine which button to click. This is where the

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