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Frequently Asked Questions

Notifying forms of global changes

Question:

How do I tell all created (and even hidden), forms of an application that some global option has changed?

Answer:

One way is to create a user message, and use the preform method to

send the message to all forms in the Screen.Forms array.



Example:



{Code for Unit1}



const

  UM_MyGlobalMessage = WM_USER + 1;



type

  TForm1 = class(TForm)

    Label1: TLabel;

    Button1: TButton;

    procedure FormShow(Sender: TObject);

    procedure Button1Click(Sender: TObject);

    { Private declarations }

  private

    procedure UMMyGlobalMessage(var AMessage: TMessage); message

      UM_MyGlobalMessage;

  public

    { Public declarations }

  end;



var

  Form1: TForm1;



implementation



{$R *.DFM}



uses Unit2;



procedure TForm1.FormShow(Sender: TObject);

begin

  Form2.Show;

end;



procedure TForm1.UMMyGlobalMessage(var AMessage: TMessage);

begin

  Label1.Left := AMessage.WParam;

  Label1.Top  := AMessage.LParam;

  Form1.Caption := 'Got It!';

end;





procedure TForm1.Button1Click(Sender: TObject);

var

  f: integer;

begin

  for f := 0 to Screen.FormCount - 1 do

    Screen.Forms[f].Perform(UM_MyGlobalMessage, 42, 42);

end;





{Code for Unit2}



const

  UM_MyGlobalMessage = WM_USER + 1;



type

  TForm2 = class(TForm)

    Label1: TLabel;

  private

    { Private declarations }

    procedure UMMyGlobalMessage(var AMessage: TMessage); message

      UM_MyGlobalMessage;

  public

    { Public declarations }

  end;



var

  Form2: TForm2;



implementation



{$R *.DFM}



procedure TForm2.UMMyGlobalMessage(var AMessage: TMessage);

begin

  Label1.Left := AMessage.WParam;

  Label1.Top  := AMessage.LParam;

  Form2.Caption := 'Got It!';

end;

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