如何使用EnumWindows的回调函数？ [英] How to use the EnumWindows call back function?

问题描述

我想有一个整洁的（密切，自包含）功能（让我们称之为GetDesktopHandle）返回的句柄桌面窗口。我用下面的code。但它仅适用于DeskHandle是一个全局变量。

如何摆脱这个全局变量的？如果我让本地I得到getDesktopWnd的AV，当我尝试DeskHandle：= hChild

  VAR DeskHandle：HWND;功能GetDesktopHandle：HWND;  功能getDesktopWnd（手柄：HWND; NOTUSED：Longint型）：BOOL; STDCALL; {回调函数}
  VAR hChild：HWND;
  开始
   如果手柄＆LT;＆GT; 0，则
    开始
      hChild：= FindWindowEx（手柄，0，'SHELLDLL_DefView'，无）;
      如果hChild＆LT;＆GT; 0，则
       开始
        hChild：= FindWindowEx（hChild，0，'SysListView32'，无）;
        如果hChild＆LT;＆GT; 0
        然后DeskHandle：= hChild;
       结束;
    结束;
   结果：= TRUE;
  结束;开始
 DeskHandle：= 0;
 EnumWindows的（@getDesktopWnd，0）;
 结果：= DeskHandle;
结束;
 

在主要问题是：我可以这样写code作为一个单一的功能，或者至少，我可以摆脱外部/全局变量的

可能的解决办法：结果
该文件说，第二个参数只是一个IN参数。

  

lParam的[输​​入]
      类型：LPARAM
      应用程序定义的值传递给回调函数。结果
  的https://msdn.microsoft.com/en-us/library/windows/desktop/ms633497%28v=vs.85%29.aspx

难道是错用它来传递，结果回来？

解决方案

 类型
  TMyData =记录
    处理：HWND;
    PID：DWORD;
    图片说明：字符串;
    产品类别：字符串;
  结束;
  PMyData = ^ TMyData;功能GetWindowClass（常量手柄：HWND）：字符串;
开始
  SetLength函数（结果，MAX_PATH）;
  SetLength函数（结果，GetClassName（手柄，PChar类型（结果），长（结果）））;
结束;功能GetWindowCaption（常量手柄：HWND）：字符串;
 开始
  SetLength函数（结果，MAX_PATH）;
  SetLength函数（结果，GetWindowText函数（手柄，PChar类型（结果），长（结果）））;
结束;功能EnumChildWindowsProc（手柄：THandle;迈德特：PMyData）：BOOL; STDCALL;
VAR
  产品类别：字符串;
  图片说明：字符串;
  PID：DWORD;
开始
  产品类别：= GetWindowClass（手柄）;
  图片说明：= GetWindowCaption（手柄）;  结果：=（类名='SysListView32'）和（标题='文件夹视图'）;
  如果结果则
  开始
    MyData.Handle：=句柄;
    GetWindowThreadProcessId（手柄，MyData.Pid）;
    MyData.Caption：=标题;
    MyData.ClassName：=类名;
  结束;  //要继续枚举，回调函数必须返回TRUE;
  //停止枚举，它必须返回FALSE
  结果：=没有结果;
结束;过程TForm1.Button1Click（发件人：TObject的）;
VAR
  迈德特：TMyData;
开始
  ZeroMemory（@MyData，一下SizeOf（迈德特））;
  EnumChildWindows（GetDesktopWindow，@EnumChildWindowsProc，NativeInt（@MyData））;
  如果MyData.Handle＆GT; 0，则
  开始
     ShowMessageFmt（'PID调节找到％d窗口，[MyData.Pid]）;
  结束
  别人开始
    ShowMessage（'窗口不存在！'）;
  结束;
结束;
 

I would like to have a single neat (close and self contained) function (let's call it GetDesktopHandle) that returns a handle to the Desktop window. I use the code below. But it only works in the DeskHandle is a global var.

How to get rid of this global variable? If I make it local I get an AV in getDesktopWnd when I try to DeskHandle := hChild

VAR DeskHandle : HWND;

function GetDesktopHandle: HWND;

  function getDesktopWnd (Handle: HWND; NotUsed: Longint): bool; stdcall;    { Callback function }
  VAR hChild : HWND;
  begin
   if handle <> 0 then
    begin
      hChild := FindWindowEx(handle, 0, 'SHELLDLL_DefView', nil);
      if hChild <> 0 then
       begin
        hChild := FindWindowEx(hChild, 0, 'SysListView32', nil);
        if hChild <> 0
        then DeskHandle := hChild;
       end;
    end;
   Result:= TRUE;
  end;

begin
 DeskHandle := 0;
 EnumWindows(@getDesktopWnd, 0);
 Result:= DeskHandle;
end;

The main question is: can I write this code as a single function or AT LEAST, can I get rid of the external/global var?

Possible solution:
The documentation says that the second parameter is only a IN parameter.

lParam [in] Type: LPARAM An application-defined value to be passed to the callback function.
https://msdn.microsoft.com/en-us/library/windows/desktop/ms633497%28v=vs.85%29.aspx

Would it be wrong to use it to pass the result back?

解决方案

type
  TMyData = record
    Handle: HWND;
    Pid: DWORD;
    Caption: String;
    ClassName: String;
  end;
  PMyData = ^TMyData;

function GetWindowClass(const Handle: HWND): String;
begin
  SetLength(Result, MAX_PATH);
  SetLength(Result, GetClassName(Handle, PChar(Result), Length(Result)));
end;

function GetWindowCaption(const Handle: HWND): String;
 begin
  SetLength(Result, MAX_PATH);
  SetLength(Result, GetWindowText(Handle, PChar(Result), Length(Result)));
end;

function EnumChildWindowsProc(Handle: THandle; MyData: PMyData): BOOL; stdcall;
var
  ClassName: String;
  Caption: String;
  Pid: DWORD;
begin
  ClassName := GetWindowClass(Handle);
  Caption := GetWindowCaption(Handle);

  Result := (ClassName = 'SysListView32') and (Caption = 'FolderView');
  if Result then
  begin
    MyData.Handle := Handle;
    GetWindowThreadProcessId(Handle, MyData.Pid);
    MyData.Caption := Caption;
    MyData.ClassName := ClassName;
  end;

  // To continue enumeration, the callback function must return TRUE;
  // to stop enumeration, it must return FALSE
  Result := not Result;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  MyData: TMyData;
begin
  ZeroMemory(@MyData, SizeOf(MyData));
  EnumChildWindows(GetDesktopWindow, @EnumChildWindowsProc, NativeInt(@MyData));
  if MyData.Handle > 0 then
  begin
     ShowMessageFmt('Found Window in Pid %d', [MyData.Pid]);
  end
  else begin
    ShowMessage('Window not found!');
  end;
end;

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