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;