把其它程序(如网页等)的文字拖放到Memo里

核心提示：原作者：Victor Chen来源：C++ 爱好者网址: http://www.cppfans.com/Email: victor@cppfans.com需要用 COM 接口的 OLE 拖放目标, 程序新建一个支持拖放目标的UnitTMyDropTarget 单元, 在这个单元里创建一个 TMyDropTarget 类

　　原作者：Victor Chen
来　源：C++ 爱好者
网址: http://www.cppfans.com/
Email: victor@cppfans.com

需要用 COM 接口的 OLE 拖放目标, 程序新建一个支持拖放目标的UnitTMyDropTarget 单元, 在这个单元里创建一个 TMyDropTarget 类。
这个程序可以使从写字板或者网页等定义的文本块用鼠标拖动, 放到程序的 Memo 里, 插入到 Memo 的拖放的位置。

首先看看如何使用这个 TMyDropTarget 类:
在 Form 的头文件里 (例如 Unit1.h) 需要增加的内容(蓝色部分是新增内容):
#include "UnitTMyDropTarget.h"

class TForm1 : public TForm
{
PRivate: // User declarations
　　TMyDropTarget *DropMemo1; //自定义的拖放目标类
　　void __fastcall DropMemo1Text(IDropTarget *Sender, AnsiString AText, DWord KeyState, TPoint pt); //拖放事件
public: // User declarations
　　__fastcall TForm1(TComponent* Owner);
　　__fastcall ~TForm1();
};

在 From 的 .cpp 文件里 (例如 Unit1.cpp), 需要增加的内容(蓝色部分是新增内容):

__fastcall TForm1::TForm1(TComponent* Owner)
: TForm(Owner)
{
　　OleInitialize(NULL);
　　DropMemo1 = new TMyDropTarget(Memo1);
　　DropMemo1->OnProcessText = DropMemo1Text;
}
//---------------------------------------------------------------------------
__fastcall TForm1::~TForm1()
{
　　DropMemo1->Release();//delete DropMemo1;
　　OleUninitialize();
}
//---------------------------------------------------------------------------
void __fastcall TForm1::DropMemo1Text(IDropTarget *Sender, AnsiString AText, DWORD KeyState, TPoint pt)
{
　　POINTS p={pt.x,pt.y};
　　*(long*)&p=SendMessage(Memo1->Handle,EM_CHARFROMPOS,0,*(long*)&p);
　　Memo1->SelStart = p.x;
　　Memo1->SelLength = 0;
　　Memo1->SelText = AText;
}
//---------------------------------------------------------------------------

TMyDropTarget 类的实现:
头文件 UnitTMyDropTarget.h 的内容:
//---------------------------------------------------------------------------
#ifndef UnitTMyDropTargetH
#define UnitTMyDropTargetH
//---------------------------------------------------------------------------
#include "oleidl.h"
#include "controls.hpp"
//---------------------------------------------------------------------------
class TMyDropTarget: public IDropTarget
{
public:
　　__property void __fastcall (__closure *OnGetFormat)(IDropTarget *Sender, IDataObject *DataObject, DWORD KeyState, TPoint pt, DWORD &dpe, bool &bDataOK) = { read=_FGetFormat, write=_FGetFormat };

　　__property void __fastcall (__closure *OnProcessData)(IDropTarget *Sender, IDataObject *DataObject, DWORD KeyState, TPoint pt) = { read=_FProcessData, write=_FProcessData };
　　__property void __fastcall (__closure *OnProcessText)(IDropTarget *Sender, AnsiString AText, DWORD KeyState, TPoint pt) = { read=_FProcessText, write=_FProcessText };
　　TMyDropTarget(TWinControl *AOwner);
　　~TMyDropTarget();
　　HRESULT __stdcall QueryInterface(const GUID &iid, void **ppv);
　　ULONG __stdcall AddRef(void) { return ++_iRefCount; }
　　ULONG __stdcall Release(void) { if(--_iRefCount==0){delete this;} return _iRefCount; }
　　HRESULT __stdcall DragEnter(IDataObject *pDataObject, DWORD grfKeyState, POINTL pt, DWORD *pdwEffect);
　　HRESULT __stdcall DragOver(DWORD grfKeyState, POINTL pt, DWORD *pdwEffect);
　　HRESULT __stdcall DragLeave(void);
　　HRESULT __stdcall Drop(IDataObject *pDataObject, DWORD grfKeyState, POINTL pt, DWORD * pdwEffect);
private:
　　ULONG _iRefCount;
　　IDataObject *_lpDataObj;
　　TWinControl *_OwnerControl;
　　void __fastcall (__closure *_FGetFormat)(IDropTarget *Sender, IDataObject *DataObject, DWORD KeyState, TPoint pt, DWORD &dpe, bool &bDataOK);
　　void __fastcall (__closure *_FProcessData)(IDropTarget *Sender, IDataObject *DataObject, DWORD KeyState, TPoint pt);
　　void __fastcall (__closure *_FProcessText)(IDropTarget *Sender, AnsiString AText, DWORD KeyState, TPoint pt);
　　bool __fastcall FDataFormatOK(DWORD KeyState, POINTL pt, DWORD &dpe);
　　void __fastcall FProcessData(DWORD KeyState, POINTL pt);
};
//---------------------------------------------------------------------------
#endif
//---------------------------------------------------------------------------

UnitTMyDropTarget.cpp 的内容:
//---------------------------------------------------------------------------
#include "UnitTMyDropTarget.h"
//---------------------------------------------------------------------------
TMyDropTarget::TMyDropTarget(TWinControl *AOwner)
{
　　_OwnerControl = AOwner;
　　_iRefCount = 0;
　　_lpDataObj = NULL;
　　_FGetFormat = NULL;
　　_FProcessData = NULL;
　　_FProcessText = NULL;

　　RegisterDragDrop(_OwnerControl->Handle,this);
}
//---------------------------------------------------------------------------
TMyDropTarget::~TMyDropTarget()
{
　　RevokeDragDrop(_OwnerControl->Handle);
}
//---------------------------------------------------------------------------
HRESULT __stdcall TMyDropTarget::QueryInterface(const GUID &iid, void **ppv)
{
　　if((iid==IID_IUnknown)(iid==IID_IDropTarget))
　　{
　　　　*ppv=this;
　　　　AddRef();
　　}
　　else
　　{
　　　　*ppv=NULL;
　　　　return E_NOINTERFACE;
　　}
　　return S_OK;
}
//---------------------------------------------------------------------------
HRESULT __stdcall TMyDropTarget::DragEnter(IDataObject *pDataObject, DWORD grfKeyState, POINTL pt, DWORD *pdwEffect)
{
　　_lpDataObj = pDataObject;
　　FDataFormatOK(grfKeyState,pt,*pdwEffect);
　　return S_OK;
}
//---------------------------------------------------------------------------
HRESULT __stdcall TMyDropTarget::DragOver(DWORD grfKeyState, POINTL pt, DWORD *pdwEffect)
{
　　FDataFormatOK(grfKeyState,pt,*pdwEffect);
　　return S_OK;
}
//---------------------------------------------------------------------------
HRESULT __stdcall TMyDropTarget::DragLeave(void)
{
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