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delphi SetWindowsHookEx inside thread

Posted on 2013-12-03
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Last Modified: 2013-12-05
Hi, im trying to hook the keyboard inside a thread.
The code works fine on the VLC form but inside the thread the hook wont work

the code is below

 type
  tagKBDLLHOOKSTRUCT = packed record // contém as informações do evento
    vkCode: DWord; // virtual key (1.254) vk_back,vk_return,etc
    scanCode: DWord;
    flags: DWord;
    time: DWord;
    dwExtraInfo: PDWord;
  end;

  TKBDLLHOOKSTRUCT = tagKBDLLHOOKSTRUCT;
  PKBDLLHOOKSTRUCT = ^TKBDLLHOOKSTRUCT;

type
  Thookbarcode = class(TThread)
  private
    apppath : string;
  protected
    procedure Execute; override;
  public
    hookhandle: HHook;
    constructor create(meubarcode : Tbarcodereader; apppath : string);
  end;

function LowLevelKeyboardHook(Code: integer; wParam: wParam; lParam: lParam)
    : longint;  stdcall;

var
  codigo: string;
  intervalo : cardinal;
  threadbarcode : Tbarcodereader;


implementation

constructor Thookbarcode.create(meubarcode: Tbarcodereader; apppath : string);
begin
  inherited create(true);
  threadbarcode := meubarcode;
  self.apppath := apppath;
  resume;

end;

function LowLevelKeyboardHook(Code: Integer; wParam: wParam; lParam: lParam)
  : longint; stdcall;
var
  p: PKBDLLHOOKSTRUCT;
begin
  p := PKBDLLHOOKSTRUCT(lParam);
  if (p.vkCode = VK_RETURN) then
  begin
  result := 1;
  exit;
  end;
  if wParam = $0100 then
  begin
    if (p.vkCode >= 48) and (p.vkCode <= 57) then
    begin
      if gettickcount - intervalo < 50 then
        codigo := codigo + Char(p.vkCode)
      else
        codigo := Char(p.vkCode);
      if length(codigo) > 7 then
      begin
        threadbarcode.add(codigo);
        codigo := '';
      end;
      Result := 1;
      intervalo := gettickcount;
      exit;
    end;
  end;
  Result := CallNextHookEx(0, Code, wParam, lParam);
end;

procedure Thookbarcode.Execute;
begin
hookhandle := SetWindowsHookEx(WH_KEYBOARD_LL, @LowLevelKeyboardHook, Hinstance, 0);
 while not terminated do
 begin
   sleep(1);
 end;
 UnHookWindowsHookEx(hookhandle);
end;

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Question by:Slinkkkk
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5 Comments
 
LVL 19

Expert Comment

by:Thommy
ID: 39694826
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LVL 19

Assisted Solution

by:MerijnB
MerijnB earned 1336 total points
ID: 39694989
Do you use TThread? It's possible the hook needs a message loop to work correctly.
What else is in this thread?
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LVL 19

Assisted Solution

by:Thommy
Thommy earned 664 total points
ID: 39695095
Probably that's the point!!!

If you call a hook in the context of a thread, the thread that installed the hook must have a message loop.

For how to implement a message loop for a thread, have a look at Unit HookThread
0
 
LVL 19

Accepted Solution

by:
MerijnB earned 1336 total points
ID: 39695169
Alternatively you can add such a method to your TThread descendant:

procedure _TThread.MessageLoop;
var Msg: TMsg;
begin
 // If GetMessage retrieves the WM_QUIT, the return value is FALSE and the message loop is broken.

 while GetMessage(Msg, 0, 0, 0) do
 begin
  TranslateMessage(Msg);
  DispatchMessage(Msg)
 end;

 inherited Terminate();
end;

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and call MessageLoop() in your execute method:
procedure _TThread.Execute;
begin
 // do init stuff

 MessageLoop();

 // do deinit stuff
end;

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You'll have to keep in mind that your thread now isn't a sync function anymore, hence my question what else you are doing in your thread.
0
 
LVL 28

Expert Comment

by:Sinisa Vuk
ID: 39695275
Why do you need threading? It can be done without thread. All hooking stuff should be placed in external dll. Hooking procedure must take callback procedure - which is working like event procedure.
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