在鼠标拖出边界后,控件如何接收鼠标事件？

Question

我创建当鼠标拖动,特别是使用的消息,其识别一个自定义的控制WM_LBUTTONDOWN,WM_LBUTTONUP和WM_MOUSEMOVE.当鼠标按下时,我捕获控件上的位置,然后当鼠标移动时,如果鼠标左键按下,我会做更多处理(在起点和终点之间计算).

问题是,我希望鼠标不受控制,甚至超出窗体,但是当鼠标离开控件时,它不再捕获鼠标事件.有没有办法可以专门处理没有鼠标控制的消息WM_MOUSEMOVE和WM_LBUTTONUP消息？

Answer 1

SetCapture/ReleaseCapture当光标移出控件时,您可以使用Windows API继续获取鼠标事件.

Answer 2

Releasecapture适用于Wincontrols,另一种方式可能是Mousehook.那只是一个演示....

unit MouseHook;
// 2012 by Thomas Wassermann
interface

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

type

  TForm3 = class(TForm)
    procedure FormDestroy(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private-Deklarationen }
  public
    { Public-Deklarationen }
  end;

var
  Form3: TForm3;

implementation

var
  HookHandle: Cardinal;

Type
  tagMSLLHOOKSTRUCT = record
    POINT: TPoint;
    mouseData: DWORD;
    flags: DWORD;
    time: DWORD;
    dwExtraInfo: DWORD;
  end;
  TMSLLHOOKSTRUCT = tagMSLLHOOKSTRUCT;
  PMSLLHOOKSTRUCT = ^TMSLLHOOKSTRUCT;

{$R *.dfm}

function LowLevelMouseProc(nCode: Integer; wParam: wParam; lParam: lParam): LRESULT; stdcall;
var
 Delta:Smallint;
begin
  if (nCode >= 0) then
  begin
    Form3.Caption := Format('X: %d  Y: %d ', [PMSLLHOOKSTRUCT(lParam)^.Point.X,  PMSLLHOOKSTRUCT(lParam)^.Point.Y]);
    if wParam = WM_LButtonDOWN then Form3.Caption := Form3.Caption + ' LD';
    if wParam = WM_LButtonUP then Form3.Caption := Form3.Caption + ' LU';
    if wParam = WM_RButtonDOWN then Form3.Caption := Form3.Caption + ' RD';
    if wParam = WM_RButtonUP then Form3.Caption := Form3.Caption + ' RU';
    if wParam =  WM_MOUSEMOVE then Form3.Caption := Form3.Caption + ' Move';
    Delta := PMSLLHOOKSTRUCT(lParam)^.mouseData shr 16;
    if wParam =  WM_MOUSEWHEEL then
          begin

            Form3.Caption := Form3.Caption + ' Wheel ' ;
            if Delta=120 then Form3.Caption := Form3.Caption + ' KLICK'
            else if Delta > 0  then Form3.Caption := Form3.Caption +' UP'
            else if Delta < 0  then Form3.Caption := Form3.Caption +' DOWN'
          end;
    if wParam =  WM_MOUSEHWHEEL then
          begin
            Form3.Caption := Form3.Caption + ' HWheel';
            if Delta=120 then Form3.Caption := Form3.Caption + ' KLICK'
            else if Delta > 0  then Form3.Caption := Form3.Caption +' UP'
            else if Delta < 0  then Form3.Caption := Form3.Caption +' DOWN'

          end;
     Form3.Caption := Form3.Caption +' >> '+ IntToStr(Delta)

  end;
  Result := CallNextHookEx(HookHandle, nCode, wParam, lParam);
end;

function InstallMouseHook: Boolean;
begin
  Result := False;
  if HookHandle = 0 then
  begin
    HookHandle := SetWindowsHookEx(WH_MOUSE_LL, @LowLevelMouseProc, hInstance, 0);
    Result := HookHandle <> 0;
  end;
end;

procedure TForm3.FormCreate(Sender: TObject);
begin
  InstallMouseHook;
end;

procedure TForm3.FormDestroy(Sender: TObject);
begin
  if HookHandle <> 0 then
    UnhookWindowsHookEx(HookHandle);
end;

end.