解释GetKeyState/GetCursorPos中的错误

Question

有时我会收到客户的错误报告,我无法解释.在Delphi中的Application.Run()之后,我收到以下错误:

 EOSError: System error: Code:_5 Access denied

 Call Stack Information:
-------------------------------------------------------------------
|Address |Module     |Unit       |Class |Procedure       |Line    |
-------------------------------------------------------------------
|Running Thread: ID=4352; Priorität=0; Klasse=; [Main Thread]     |
|-----------------------------------------------------------------|
|772B291F|USER32.dll |           |      |GetKeyState     |        |
|772B7B96|USER32.dll |           |      |GetPropA        |        |
|772B7B5A|USER32.dll |           |      |GetPropA        |        |
|772A7BC5|USER32.dll |           |      |DispatchMessageA|        |
|772A7BBB|USER32.dll |           |      |DispatchMessageA|        |
|00A6D804|Program.exe|Program.dpr|      |                |803[369]|  // Application.Run
-------------------------------------------------------------------

和

EOsError: A call to an OS function failed

Call Stack Information:
-------------------------------------------------------------------
|Address |Module     |Unit       |Class |Procedure       |Line    |
-------------------------------------------------------------------
|Running Thread: ID=2712; Priorität=0; Klasse=; [Main Thread]     |
|-----------------------------------------------------------------|
|7E379758|USER32.dll |           |      |GetCursorPos    |        |
|7E379ED9|USER32.dll |           |      |GetKeyState     |        |
|7E37B3FC|USER32.dll |           |      |CallNextHookEx  |        |
|7E380078|USER32.dll |           |      |GetPropA        |        |
|7E380042|USER32.dll |           |      |GetPropA        |        |
|7E3696C2|USER32.dll |           |      |DispatchMessageA|        |
|7E3696B8|USER32.dll |           |      |DispatchMessageA|        |
|00A6E823|Program.exe|Program.dpr|      |                |803[369]|  //Application.Run
-------------------------------------------------------------------

在这两种情况下,从Eurekalog提交的屏幕截图都是黑色的.

任何人都可以解释一下,这会导致GetCursorPos或GetKeyState失败的原因是什么？

Answer 1

文档GetCursorPos说:

当您调用GetCursorPos时,输入桌面必须是当前桌面.调用OpenInputDesktop以确定当前桌面是否为输入桌面.如果不是,请使用OpenInputDesktop返回的HDESK调用SetThreadDesktop切换到该桌面.

在解锁工作站时,最常见的是犯规.在我的代码中,我替换GetCursorPos为此变体:

function GetCursorPos(var lpPoint: TPoint): BOOL; stdcall;
(* The GetCursorPos API in user32 fails if it is passed a memory address >2GB 
   which breaks LARGEADDRESSAWARE apps.  We counter this by calling GetCursorInfo
   instead which does not suffer from the same problem.

   In addition we have had problems with GetCursorPos failing when called 
   immediately after a password protected screensaver or a locked workstation 
   re-authenticates. This problem initially appeared with XP SP1 and is brought 
   about because TMouse.GetCursorPos checks the return value of the GetCursorPos 
   API call and raises an OS exception if the API has failed.
*)
var
  CursorInfo: TCursorInfo;
begin
  CursorInfo.cbSize := SizeOf(CursorInfo);
  Result := GetCursorInfo(CursorInfo);
  if Result then begin
    lpPoint := CursorInfo.ptScreenPos;
  end else begin
    lpPoint := Point(0, 0);
  end;
end;

您可以使用自己喜欢的代码挂钩机制来替换GetCursorPos.我是这样做的:

RedirectProcedure(@Windows.GetCursorPos, @CodePatcher.GetCursorPos);

与RedirectProcedure此处描述:补丁德尔福日常通话

事实证明,对于我的特定情况,这GetCursorPos将失败,但GetCursorInfo不会失败.但正如评论中指出的那样,有些情况GetCursorInfo也会失败.在这种情况下,您可能会发现安排补丁函数不返回是有利的False.

至于GetKeyState,我不确定那一个.它可能很相似,但是GetKeyState我个人并不熟悉的API.