Using VCL TTimer in Delphi console application

Question

As the question subject says. I have a console application in Delphi, which contains a TTimer variable. The thing I want to do is assign an event handler to T

Answer 1

As others have mentioned, console applications don't have a message pump.

Here is a TConsoleTimer thread class which mimics a TTimer class. The main difference is that the code in the event is executed in the TConsoleTimer thread.

Update

At the end of this post is a way to have this event called in the main thread.

unit ConsoleTimer;

interface

uses
  Windows, Classes, SyncObjs, Diagnostics;

type
  TConsoleTimer = Class(TThread)
  private
    FCancelFlag: TSimpleEvent;
    FTimerEnabledFlag: TSimpleEvent;
    FTimerProc: TNotifyEvent; // method to call
    FInterval: integer;
    procedure SetEnabled(doEnable: boolean);
    function GetEnabled: boolean;
    procedure SetInterval(interval: integer);
  protected
    procedure Execute; override;
  public
    Constructor Create;
    Destructor Destroy; override;
    property Enabled : boolean read GetEnabled write SetEnabled;
    property Interval: integer read FInterval write SetInterval;
    // Note: OnTimerEvent is executed in TConsoleTimer thread
    property OnTimerEvent: TNotifyEvent read FTimerProc write FTimerProc;
  end;

implementation

constructor TConsoleTimer.Create;
begin
  inherited Create(false);
  FTimerEnabledFlag := TSimpleEvent.Create;
  FCancelFlag := TSimpleEvent.Create;
  FTimerProc := nil;
  FInterval := 1000;
  Self.FreeOnTerminate := false; // Main thread controls for thread destruction
end;

destructor TConsoleTimer.Destroy; // Call TConsoleTimer.Free to cancel the thread
begin
  Terminate; 
  FTimerEnabledFlag.ResetEvent; // Stop timer event
  FCancelFlag.SetEvent; // Set cancel flag
  Waitfor; // Synchronize
  FCancelFlag.Free;
  FTimerEnabledFlag.Free;
  inherited;
end;

procedure TConsoleTimer.SetEnabled(doEnable: boolean);
begin
  if doEnable then
    FTimerEnabledFlag.SetEvent
  else
    FTimerEnabledFlag.ResetEvent;
end;

procedure TConsoleTimer.SetInterval(interval: integer);
begin
  FInterval := interval;
end;

procedure TConsoleTimer.Execute;
var
  waitList: array [0 .. 1] of THandle;
  waitInterval,lastProcTime: Int64;
  sw: TStopWatch;
begin
  sw.Create;
  waitList[0] := FTimerEnabledFlag.Handle;
  waitList[1] := FCancelFlag.Handle;
  lastProcTime := 0;
  while not Terminated do
  begin
    if (WaitForMultipleObjects(2, @waitList[0], false, INFINITE) <>
      WAIT_OBJECT_0) then
      break; // Terminate thread when FCancelFlag is signaled
    if Assigned(FTimerProc) then
    begin
      waitInterval := FInterval - lastProcTime;
      if (waitInterval < 0) then
        waitInterval := 0;
      if WaitForSingleObject(FCancelFlag.Handle,waitInterval) <> WAIT_TIMEOUT then
        break;

      if WaitForSingleObject(FTimerEnabledFlag.Handle, 0) = WAIT_OBJECT_0 then
      begin
        sw.Start;
        FTimerProc(Self);
        sw.Stop;
        // Interval adjusted for FTimerProc execution time
        lastProcTime := sw.ElapsedMilliSeconds;
      end;
    end;
  end;
end;

function TConsoleTimer.GetEnabled: boolean;
begin
  Result := (FTimerEnabledFlag.Waitfor(0) = wrSignaled);
end;

end.

And a test:

program TestConsoleTimer;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils,ConsoleTimer;

type
  TMyTest = class
    procedure MyTimerProc(Sender: TObject);
  end;

procedure TMyTest.MyTimerProc(Sender: TObject);
begin
  // Code executed in TConsoleTimer thread !
  WriteLn('Timer event');
end;

var
  MyTest: TMyTest;
  MyTimer: TConsoleTimer;
begin
  MyTest := TMyTest.Create;
  try
    MyTimer := TConsoleTimer.Create;
    MyTimer.Interval := 1000;
    MyTimer.OnTimerEvent := MyTest.MyTimerProc;
    WriteLn('Press [Enter] key to end.');
    MyTimer.Enabled := true;
    ReadLn;
    MyTimer.Free;
  finally
    MyTest.Free;
    WriteLn('End.');
  end;
end.

---

As mentioned above, how do I make the event execute in the main thread?

Reading Delphi 7: Handling events in console application (TidIRC) gives the answer.

Add a method in TConsoleTimer:

procedure TConsoleTimer.SwapToMainThread;
begin
  FTimerProc(Self);
end;

and change the call in the Execute method to:

Synchronize(SwapToMainThread);

To pump the synchronized calls, use CheckSynchronize() function in Classes unit:

while not KeyPressed do CheckSynchronize(); // Pump the synchronize queue

Note: the console KeyPressed function can be found here:How i can implement a IsKeyPressed function in a delphi console application?.