1. Computing

Get the Control Under the Mouse in a Delphi application

How to know what Control is Under the Mouse in a Delphi application


If, in your Delphi application you need to know what control is "under" the mouse while the mouse is being moved over the application, you can use RTL's FindVCLWindow function.


The VCLWindow function can locate the windowed control under a certain point - for example under the mouse pointer. You can use FindVCLWindow to identify the windowed control that is under the mouse from another control that has captured the mouse. The Pos parameter specifies the location that must be over the returned windowed control. If there is no windowed control under the Pos parameter, FindVCLWindow returns nil.

For an example have a TApplicationEvents component on the main form of the application and handle its OnIdle event as:

 //Handles OnIdle event of the ApplicationEvents1 control the MainForm
 procedure TMainForm.ApplicationEvents1Idle(Sender: TObject; var Done: Boolean) ;
   ctrl : TWinControl;
   ctrl := FindVCLWindow(Mouse.CursorPos) ;
   if ctrl <> nil then
     Caption := ctrl.Name;
     //do something if mouse is over TLabeledEdit
     if ctrl is TLabeledEdit then
       Caption := TLabeledEdit(ctrl).Text;

Note: Mouse.CursorPos returns the coordinate of the mouse pointer related to the screen. Delphi tips navigator:
» Controling the Number of a Delphi application Instances on a Terminal Server
« Graphical Progress Bar for Delphi applications - Partial / Continuous Move

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