How to get a delphi application (that's running) to do something at a particular time/date

Question

My application sits in the system tray when it\'s not being used.

The user can configure events to occur at particular schedule. For example they may way the task p

Answer 1

Another option would be to create a TThread which performs the management of the timer:

type
  TestThreadMsg = class(tThread)
  private
    fTargetDate : tDateTime;
    fMsg : Cardinal;
  protected
    procedure Execute; override;
    procedure NotifyApp;
  public
    constructor Create( TargetDate : TDateTime; Msg:Cardinal);
  end;

implementation:

constructor TestThreadMsg.Create(TargetDate: TDateTime; Msg: Cardinal);
begin
  inherited Create(True);
  FreeOnTerminate := true;
  fTargetDate := TargetDate;
  fMsg := Msg;
  Suspended := false;
end;

procedure TestThreadMsg.Execute;
begin
  Repeat
    if Terminated then exit;
    if Now >= fTargetDate then
      begin
        Synchronize(NotifyApp);
        exit;
      end;
    Sleep(1000); // sleep for 1 second, resoultion = seconds
  Until false;
end;

procedure TestThreadMsg.NotifyApp;
begin
  SendMessage(Application.MainForm.Handle,fMsg,0,0);
end;

Which can then be hooked up to the main form:

const
  WM_TestTime = WM_USER + 1;

TForm1 = Class(TForm)
  :
  procedure FormCreate(Sender: TObject);
  procedure WMTestTime(var Msg:tMessage); message WM_TestTime;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  TestThreadMsg.Create(IncSecond(Now,5),WM_TestTime);
end;

procedure TForm1.WMTestTime(var Msg: tMessage);
begin
  ShowMessage('Event from Thread');
end;