unitcreateevent.pas

Delphi Win32核心API参考光盘源码 本书包含了常用的Windows API函数

unit UnitCreateEvent;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    Button4: TButton;
    Label1: TLabel;
    Button5: TButton;
    Label2: TLabel;
    Label3: TLabel;
    Label4: TLabel;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
    procedure Button4Click(Sender: TObject);
    procedure Button5Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  EventHandle: THandle;     // holds the event handle
  ThreadHandle: THandle;    // holds the thread handle

implementation

{$R *.DFM}     

function ThreadFunction(Info: Pointer): Integer; stdcall;
var
  FormDC: HDC;         // holds a handle to the form device context
  Counter: Integer;    // general loop counter
  CounterStr: string;  // a string representation of the loop counter
  ObjRtn: Integer;     // wait function return value
begin
  {WaitForSingleObject will wait for the event to
   become signaled (ready to do something)}
  ObjRtn := WaitForSingleObject(EventHandle, INFINITE);

  {retrieve a handle to the form's device context}
  FormDC := GetDC(Form1.Handle);

  {begin a large loop}
  for Counter := 1 to 100000 do
  begin
    {display the counter value}
    CounterStr := IntToStr(Counter);
    TextOut(FormDC, 10, 10, PChar(CounterStr), Length(CounterStr));

    {process any pending messages}
    Application.ProcessMessages;

    {this causes the loop to pause, as the PulseEvent function
     rapidly sets the event's signaled state to signaled and
     then unsignaled}
    ObjRtn := WaitForSingleObject(EventHandle, INFINITE);
  end;

  {release the form's device context and exit the thread}
  ReleaseDC(Form1.Handle, FormDC);
  ExitThread(4);
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  ThreadID: DWORD;    // holds the thread identifier
begin
  {create a new thread}
  ThreadHandle := CreateThread(nil, 0, @ThreadFunction, nil, 0, ThreadId);
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  {indicate that the event is signaled.  this will cause the waiting
   thread to get past the WaitForSingleObject function, thus starting
   the loop}
  SetEvent(EventHandle);
  Label1.Caption := 'Event is signaled';
end;

procedure TForm1.Button3Click(Sender: TObject);
begin
  {reset the event object to a non signaled state.  this will
   cause the thread loop to pause at the WaitForSingleObject
   function inside the loop}
  ResetEvent(EventHandle);
  Label1.Caption := 'Event is non signaled';
end;

procedure TForm1.Button4Click(Sender: TObject);
begin
  {if the event has been reset (above), the thread's loop will be
   paused at the internal WaitForSingleObject function. PulseEvent
   will toggle the event's state from nonsignaled to signaled and back,
   causing the thread's loop to fire once.}
  PulseEvent(EventHandle); //Set to signaled and then nonsignaled
  Label1.Caption := 'signaled/nonsignaled';
end;

procedure TForm1.Button5Click(Sender: TObject);
begin
  {create the event}
  EventHandle := CreateEvent(Nil, True, False, 'MyEvent');
end;

end.