Moving controls at runtime

Question:

How can I move a control at runtime using the mouse?

Answer:

You can trap the OnMouseDown event, remembering the x and y coordinates of the mouse and set the mouse capture. You can then track mouse movements with the OnMouseMove event, moving the control until the OnMouseUp event is fired. You then will want to place the control in it's final position and release capture of the mouse.

The following example shows how to move a TButton component around on the form using the mouse. The movement is initiated by the user holding down the control key when the mouse button is activated.

Example:

type

TForm1 = class(TForm)

Button1: TButton;

procedure Button1MouseDown(Sender: TObject; Button: TMouseButton;

Shift: TShiftState; X, Y: Integer);

procedure Button1MouseMove(Sender: TObject; Shift: TShiftState; X,

Y: Integer);

procedure Button1MouseUp(Sender: TObject; Button: TMouseButton;

Shift: TShiftState; X, Y: Integer);

private

{ Private declarations }

public

{ Public declarations }

MouseDownSpot : TPoint;

Capturing : bool;

end;

var

Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.Button1MouseDown(Sender: TObject;

Button: TMouseButton; Shift: TShiftState; X, Y: Integer);

begin

if ssCtrl in Shift then begin

SetCapture(Button1.Handle);

Capturing := true;

MouseDownSpot.X := x;

MouseDownSpot.Y := Y;

end;

procedure TForm1.Button1MouseMove(Sender: TObject;

Shift: TShiftState; X, Y: Integer);

begin

if Capturing then begin

Button1.Left := Button1.Left - (MouseDownSpot.x - x);

Button1.Top := Button1.Top - (MouseDownSpot.y - y);

end;

procedure TForm1.Button1MouseUp(Sender: TObject; Button: TMouseButton;

Shift: TShiftState; X, Y: Integer);

begin

if Capturing then begin

ReleaseCapture;

Capturing := false;

Button1.Left := Button1.Left - (MouseDownSpot.x - x);

Button1.Top := Button1.Top - (MouseDownSpot.y - y);

end;