TShape.OnMouseDown Event

Occurs when the user presses a mouse button with the mouse pointer over a control.

Pascal

property OnMouseDown: TMouseEvent;

C++

__property TMouseEvent OnMouseDown;

Description

Use the OnMouseDown event handler to implement any special processing that should occur as a result of pressing a mouse button.

The OnMouseDown event handler can respond to left, right, or center mouse button presses and shift key plus mouse-button combinations. Shift keys are the Shift, Ctrl, and Alt keys. X and Y are the pixel coordinates of the mouse pointer in the client area of the Sender.

C++ Examples:

Copy Code

/*
The following example requires a form with a four-paneled
status bar.  (Set the Width of the status panels to 150
before running this example).  When the user presses a mouse
button, moves the mouse, and releases the mouse button, a
rectangle is drawn on the form. When the mouse button is
released, the rectangle appears on the form’s canvas. Its
top-left and bottom-right corners are defined by the
location of the mouse pointer when the user pressed and
released the mouse button.  While the user drags the mouse,
the location of the top, left, bottom, and right sides of
the rectangle are displayed in the status bar.
*/ 
int StartX, StartY; // Declare at the top of the form’s unit
// Use this code as the OnMouseDown event handler of the form:
void __fastcall TForm1::FormMouseDown(TObject *Sender, TMouseButton Button, TShiftState Shift, int X, int Y)
{
  StartX = X;
  StartY = Y;
}

// Use this code as the OnMouseUp event handler of the form:
void __fastcall TForm1::FormMouseUp(TObject *Sender, TMouseButton Button, TShiftState Shift, int X, int Y)
{
  Form1->Canvas->Rectangle(StartX, StartY, X, Y);
  StatusBar1->Panels->Items[0]->Text = "";
  StatusBar1->Panels->Items[1]->Text = "";
  StatusBar1->Panels->Items[2]->Text = "";
  StatusBar1->Panels->Items[3]->Text = "";
}

// Use this code as the OnMouseMove event handler of the form:
void __fastcall TForm1::FormMouseMove(TObject *Sender, TShiftState Shift, int X, int Y)
{
  if (Shift.Contains(ssLeft)) // make sure button is down
  {
    if (Y > StartY)
    {
      StatusBar1->Panels->Items[0]->Text = "Top: " + IntToStr(StartY);
      StatusBar1->Panels->Items[2]->Text = "Bottom: " + IntToStr(Y);
    }
    else
    {
      StatusBar1->Panels->Items[0]->Text = "Top: " + IntToStr(Y);
      StatusBar1->Panels->Items[2]->Text = "Bottom: " + IntToStr(StartY);
    }
    if (X > StartX)
    {
      StatusBar1->Panels->Items[1]->Text = "Left: " + IntToStr(StartX);
      StatusBar1->Panels->Items[3]->Text = "Right: " + IntToStr(X);
    }
    else
    {
      StatusBar1->Panels->Items[1]->Text = "Left: " + IntToStr(X);
      StatusBar1->Panels->Items[3]->Text = "Right: " + IntToStr(StartX);
    }
  }
}

Delphi Examples:

Copy Code

{
The following example requires a form with a four-paneled
status bar.  (Set the Width of the status panels to 150
before running this example).  When the user presses a mouse
button, moves the mouse, and releases the mouse button, a
rectangle is drawn on the form. When the mouse button is
released, the rectangle appears on the form’s canvas. Its
top-left and bottom-right corners are defined by the
location of the mouse pointer when the user pressed and
released the mouse button.  While the user drags the mouse,
the location of the top, left, bottom, and right sides of
the rectangle are displayed in the status bar.
} 
procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
  StartX := X;
  StartY := Y;
end;

procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
  Form1.Canvas.Rectangle(StartX, StartY, X, Y);
  StatusBar1.Panels[0].Text := '';
  StatusBar1.Panels[1].Text := '';
  StatusBar1.Panels[2].Text := '';
  StatusBar1.Panels[3].Text := '';
end;

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
begin
  if ssLeft in Shift then { make sure button is down }
  begin
    if Y > StartY then
      begin
      StatusBar1.Panels[0].Text := 'Top: ' + IntToStr(StartY);
      StatusBar1.Panels[2].Text := 'Bottom: ' + IntToStr(Y);
      end
    else
      begin
      StatusBar1.Panels[0].Text := 'Top: ' + IntToStr(Y);
      StatusBar1.Panels[2].Text := 'Bottom: ' + IntToStr(StartY);
      end;
    if X > StartX then
      begin
      StatusBar1.Panels[1].Text := 'Left: ' + IntToStr(StartX);
      StatusBar1.Panels[3].Text := 'Right: ' + IntToStr(X);
      end
    else
      begin
      StatusBar1.Panels[1].Text := 'Left: ' + IntToStr(X);
      StatusBar1.Panels[3].Text := 'Right: ' + IntToStr(StartX);
      end;
  end;
end;