关于组件制作的问题：

Question

看来c++ builder和Delphi论坛对组件有研究的人比较少。

Answer 1

问题差不多已被我找到了。因为我对两个组件进行比较发现：TDBLookupComboBox和TDBComboBox发现，首先它们的继承的类层次不同，其中TDBComboBox的继承层次有TCustomComboBox（而这个类是TComboBox的父类），而TDBLookupComboBox的最直接父类就是TCustomControl，这恰恰证明TDBLookupComboBox是放在Paint函数中被画出来的。而我的错误代码是从TWinControl继承下来的，而父类为TWinControl控件的最大特点就是自已能够画出自已，而TCustomControl则需要自已画自已（用Paint方法）,据此可以判断TDBLookupComboBox为什么在设计期间就已经有了句柄的理由就是在从TCustomControl继承的过程序，TDBLookupComboBox不仅重载了Paint方法，还重载了CreateWnd方法。而如果你从TWinControl继承，再动态生成一个TDBLookupComboBox就会出现错误提示”该控件没有父窗口“。
欢迎各位网友参与讨论。

Answer 2

我将我的代码贴如下：
//---------------------------------------------------------------------------#ifndef KingKingH
#define KingKingH
//---------------------------------------------------------------------------
#include <SysUtils.hpp>
#include <Controls.hpp>
#include <Classes.hpp>
#include <Forms.hpp>
#include <dsgnintf.hpp>
//---------------------------------------------------------------------------
class PACKAGE TKingKing : public TCustomControl
{
private:
        TDBLookupComboBox *FLookup;
        TEdit *FEdit;
        TDataSource *FDataSource;
        TDataSource *FListSource;
        AnsiString FListField;
        AnsiString FKeyField;
        AnsiString FDataField;protected:
        virtual void __fastcall Paint();
        virtual __fastcall ~TKingKing();
public:
        __fastcall TKingKing(TComponent* Owner);
        void __fastcall SetDataSource(TDataSource *DataSource);
        void __fastcall SetListSource(TDataSource *DataSource);
        void __fastcall SetKeyField(AnsiString Field);
        void __fastcall SetDataField(AnsiString Field);
        void __fastcall SetListField(AnsiString Field);__published:
        __property TDataSource* DataSource={read=FDataSource,write=SetDataSource};
        __property TDataSource *ListSource={read=FListSource,write=SetListSource};
        __property AnsiString KeyField={read=FKeyField,write=SetKeyField};
        __property AnsiString ListField={read=FListField,write=SetListField};
        __property AnsiString DataField={read=FDataField,write=SetDataField};
};
//DataField PropertyEditor
class TDataFieldProperty:public TStringProperty
{
public:
   TPropertyAttributes __fastcall GetAttributes()
   {
        return TPropertyAttributes()<<paValueList;
   }
   void __fastcall GetValues(TGetStrProc Proc)
   {
        Proc("None");
        TDataSet *pDataSet;
        TKingKing *pDCBX=dynamic_cast<TKingKing*>(GetComponent(0));
        if(pDCBX)
        {       if(pDCBX->DataSource)
                {
                        pDataSet=pDCBX->DataSource->DataSet;
                        if(pDataSet)
                        {
                                TStrings *pList=new TStringList();
                                pDataSet->GetFieldNames(pList);                                for(int i=0;i<pList->Count;i++)
                                {
                                        Proc(pList->Strings[i]);
                                }
                                delete pList;
                        }
                }
        }
   }
};
//ListField PropertyEditor
class TListFieldProperty:public TStringProperty
{
public:
   TPropertyAttributes __fastcall GetAttributes()
   {
        return TPropertyAttributes()<<paValueList;
   }
   void __fastcall GetValues(TGetStrProc Proc)
   {
        Proc("None");
        TDataSet *pDataSet;
        TKingKing *pDCBX=dynamic_cast<TKingKing*>(GetComponent(0));
        if(pDCBX)
        {       if(pDCBX->ListSource)
                {
                pDataSet=pDCBX->ListSource->DataSet;
                if(pDataSet)
                {
                       TStrings *pList=new TStringList();
                       pDataSet->GetFieldNames(pList);
                       for(int i=0;i<pList->Count;i++)
                       {
                                Proc(pList->Strings[i]);
                       }
                       delete pList;
                }
                }
        }
   }
};
//KeyField PropertyEditor
class TKeyFieldProperty:public TStringProperty
{
public:
   TPropertyAttributes __fastcall GetAttributes()
   {
        return TPropertyAttributes()<<paValueList;
   }
   void __fastcall GetValues(TGetStrProc Proc)
   {
        Proc("None");
        TDataSet *pDataSet;
        TKingKing *pDCBX=dynamic_cast<TKingKing*>(GetComponent(0));
        if(pDCBX)
        {       if(pDCBX->ListSource)
                {
                pDataSet=pDCBX->ListSource->DataSet;
                if(pDataSet)
                {
                       TStrings *pList=new TStringList();
                       pDataSet->GetFieldNames(pList);
                       for(int i=0;i<pList->Count;i++)
                       {
                                Proc(pList->Strings[i]);
                       }
                       delete pList;
                }
                }
        }
   }
};//---------------------------------------------------------------------------
#endif
.cpp File
//---------------------------------------------------------------------------#include <vcl.h>
#pragma hdrstop#include "KingKing.h"
#pragma package(smart_init)
//---------------------------------------------------------------------------
// ValidCtrCheck is used to assure that the components created do not have
// any pure virtual functions.
//static inline void ValidCtrCheck(TKingKing *)
{
        new TKingKing(NULL);
}
//---------------------------------------------------------------------------
TTypeInfo *AnsiStringInfo()
{
        TTypeInfo *pTypeInfo=new TTypeInfo;
        pTypeInfo->Kind=tkLString;
        pTypeInfo->Name="AnsiString";
        return pTypeInfo;
}__fastcall TKingKing::TKingKing(TComponent* Owner)
        : TCustomControl(Owner)
{
        FLookup=new TDBLookupComboBox(this);
        FEdit=new TEdit(this);
        Width = 150;
        Height=46;}
//---------------------------------------------------------------------------
void __fastcall TKingKing::Paint()
{                Width = 150;
                Height=46;
                FLookup->Parent=this;
                FLookup->Left=0;
                FLookup->Top=0;
                FLookup->Width=145;
                FLookup->Height=21;                FEdit->Parent=this;
                FEdit->Left=0;
                FEdit->Top=FLookup->Height;
                FEdit->Width=80;
                FEdit->Height=21;
}
void __fastcall TKingKing::SetDataSource(TDataSource *DataSource)
{
        FDataSource=DataSource;
}
//--------------------------------------------------------------------------
void __fastcall TKingKing::SetListSource(TDataSource *DataSource)
{
        FListSource=DataSource;
}
//--------------------------------------------------------------------------
void __fastcall TKingKing::SetKeyField(AnsiString Field)
{
        FKeyField=Field;
}
void __fastcall TKingKing::SetListField(AnsiString Field)
{
        FListField=Field;
}
void __fastcall TKingKing::SetDataField(AnsiString Field)
{
        FDataField=Field;
}__fastcall TKingKing::~TKingKing()
{
        if(FLookup)
        {
                delete FLookup;
        }
        if(FEdit)
        {
                delete FEdit;
        }
        
}
namespace Kingking
{
        void __fastcall PACKAGE Register()
        {
                 TComponentClass classes[1] = {__classid(TKingKing)};
                 RegisterPropertyEditor(AnsiStringInfo(),__classid(TKingKing),"DataField",__classid(TDataFieldProperty));
                 RegisterPropertyEditor(AnsiStringInfo(),__classid(TKingKing),"ListField",__classid(TListFieldProperty));
                 RegisterPropertyEditor(AnsiStringInfo(),__classid(TKingKing),"KeyField",__classid(TKeyFieldProperty));
                 RegisterComponents("AKing", classes, 0);
        }
}
//---------------------------------------------------------------------------

Answer 3

OK，很不错，应该从TCustomControl中继承。