我用NEW 新建一个自己的控件， 为何出错？

[sdjifeng]

//---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Unit2.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
: TForm(Owner)
{
}
//---------------------------------------------------------------------------

void __fastcall TForm1::Button1Click(TObject *Sender)
{
int f;
String fn;
if(OpenDialog1->Execute())
{
fn=OpenDialog1->FileName;

f=FileOpen(fn,fmOpenRead);
FileClose(f);
Memo1->Lines->LoadFromFile(fn); }
}
//---------------------------------------------------------------------------

void __fastcall TForm1::FormCreate(TObject *Sender)
{
Memo2 = new TMemo2 ((TForm *) Sender) ;
}
//---------------------------------------------------------------------------




//---------------------------------------------------------------------------

#ifndef Unit2H
#define Unit2H
//---------------------------------------------------------------------------
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>
#include <Dialogs.hpp>
//---------------------------------------------------------------------------
class TForm1 : public TForm
{
__published: // IDE-managed Components
TButton *Button1;
TOpenDialog *OpenDialog1;
TMemo *Memo1;
void __fastcall Button1Click(TObject *Sender);
void __fastcall FormCreate(TObject *Sender);
private: // User declarations
TMemo * TMemo2;
public: // User declarations
__fastcall TForm1(TComponent* Owner);
};
//---------------------------------------------------------------------------
extern PACKAGE TForm1 *Form1;
//---------------------------------------------------------------------------
#endif
class TMemo2 : public TMemo
{ private:
unsigned int size ;
};






[C++ Error] Unit2.cpp(34): E2451 Undefined symbol 'Memo2'
[C++ Error] Unit2.cpp(34): E2303 Type name expected
[C++ Error] Unit2.cpp(34): E2379 Statement missing ;

[whitelion]

Memo2 = new TMemo2 ((TForm *) Sender) ;
改为
Memo2 = new TMemo ((TForm *) Sender) ;

[whitelion]

TMemo * TMemo2;
改为：
TMemo * Memo2;

[kingcaiyao]

代码看起来很混乱，这样：
//---------------------------------------------------------------------------

#ifndef Unit2H
#define Unit2H
//---------------------------------------------------------------------------
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>
#include <Dialogs.hpp>
//---------------------------------------------------------------------------
class TForm1 : public TForm
{
__published: // IDE-managed Components
TButton *Button1;
TOpenDialog *OpenDialog1;
TMemo *Memo1;
void __fastcall Button1Click(TObject *Sender);
void __fastcall FormCreate(TObject *Sender);
private: // User declarations
TMemo * TMemo2;
public: // User declarations
__fastcall TForm1(TComponent* Owner);
};
//---------------------------------------------------------------------------
extern PACKAGE TForm1 *Form1;
//---------------------------------------------------------------------------
#endif
class TMemo2 : public TMemo
{ private:
unsigned int size ;
};
改成：
//---------------------------------------------------------------------------

#ifndef Unit2H
#define Unit2H
//---------------------------------------------------------------------------
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>
#include <Dialogs.hpp>
//---------------------------------------------------------------------------
class TForm1 : public TForm
{
__published: // IDE-managed Components
TButton *Button1;
TOpenDialog *OpenDialog1;
TMemo *Memo1;
void __fastcall Button1Click(TObject *Sender);
void __fastcall FormCreate(TObject *Sender);
private: // User declarations
TMemo * TMemo2;
public: // User declarations
__fastcall TForm1(TComponent* Owner);
};
class TMemo2 : public TMemo
{ private:
unsigned int size ;
};

//---------------------------------------------------------------------------
extern PACKAGE TForm1 *Form1;
//---------------------------------------------------------------------------
#endif

[whitelion]

把
class TMemo2 : public TMemo
{ private:
unsigned int size ;
};
放在
TForm1 *Form1;
之前
把TMemo * TMemo2;
改为TMemo2 * Memo2;

[kingcaiyao]

oh，对了楼上说的对，应该放在前面，没看清楚，不好意思：

[chinagy]

1.头文件写错了,#endif 应放在最后一行;
2.调用时
void __fastcall TForm1::FormCreate(TObject *Sender)
{
Memo2 = new TMemo2 (this) ;
Memo2->Parent = Form1;
Memo2->Show;
}

[sdjifeng]

谢谢大家，我已经该过了，但怎么仍出错？

//---------------------------------------------------------------------------

#ifndef Unit2H
#define Unit2H
//---------------------------------------------------------------------------
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>
#include <Dialogs.hpp>
class TMemo2 : public TMemo //手工兴建一个Memo2
{
private:
unsigned int size ; //加入一个属性，仅仅是测试用
};

//---------------------------------------------------------------------------
class TForm1 : public TForm
{
__published: // IDE-managed Components
TButton *Button1;
TOpenDialog *OpenDialog1;
TMemo *Memo1; // 它的用处仅仅是与Memo2比较，
void __fastcall Button1Click(TObject *Sender);
void __fastcall FormCreate(TObject *Sender);
private:
TMemo2 * Memo2;
// TMemo * TMemo2;
public:
__fastcall TForm1(TComponent* Owner);
};
//---------------------------------------------------------------------------
extern PACKAGE TForm1 *Form1;
//---------------------------------------------------------------------------
#endif




//---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Unit2.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
: TForm(Owner)
{
}
//---------------------------------------------------------------------------

void __fastcall TForm1::Button1Click(TObject *Sender)
{
String fn;
if(OpenDialog1->Execute())
{ fn=OpenDialog1->FileName;
//Memo1->Lines->LoadFromFile(fn); //这样用大家都会
Memo2->Lines->LoadFromFile(fn);
}
}
//---------------------------------------------------------------------------


void __fastcall TForm1::FormCreate(TObject *Sender)
{
Memo2 = new TMemo2 (this) ; //系统报告error
Memo2->Parent = Form1;
Memo2->Top=200;
Memo2->Width =49;
Memo2->Left=150;
Memo2->Height=100;
Memo2->Show;

}
//---------------------------------------------------------------------------




// [C++ Error] Unit2.cpp(33): E2125 Compiler could not generate default constructor for class 'TMemo2'
// [C++ Error] Unit2.cpp(35): E2235 Member function must be called or its address taken

[ThinkX]

TMemo2没有默认的构造函数，自己写一个了。

[christopher_hp]

TMemo *Memo2=new TMemo(NULL);//如果NULL不行就用this
Memo2->Parent=Form1;
在设置它的Top,Left,Height,Width属性
不需要Memo2->Show()这样做
最后看看，需要添加头文件不，自己看看帮助

[gyj_china]

只要把 Memo2 = new TMemo2 ((TForm *) Sender) ;
改成 Memo2 = new TMemo (this);就可以了。

[Currency]

我觉得这样可能好理解

Memo2 = new TMemo2(this);
Memo2->Parent = Form1;

[IT-司马青衫]

class TMemo2 : public TMemo
{ private:
unsigned int size ;
};
放在这之前
class TForm1 : public TForm
这是C++或C数据类型向前声明

void __fastcall TForm1::FormCreate(TObject *Sender)
{
Memo2 = new TMemo2 ((TForm *) Sender) ;//因改放在构造函数中
}
//你这个是重载VCL的MEMO类
//NEW时调用默认的构造函数
//Memo2=new TMemo2(this);//THIS表示谁拥有该类的对象

fn=OpenDialog1->FileName;

f=FileOpen(fn,fmOpenRead);//
FileClose(f);//这两行代码多余的，如果采用其它方式来就需要句柄
Memo1->Lines->LoadFromFile(fn); }

[sdjifeng]

谢谢xi8kuang
TMemo *Memo2=new TMemo(this);//
Memo2->Parent = Form1;
是可行的。
但是Memo2仅仅在 TForm1::FormCreate中可用，
在TForm1::Button1Click()中就不可用了，变成了NULL,好奇怪。
我应怎么办？

[sdjifeng]

我发现使用以下代码可以解决问题
MyMemo1 = new TMyMemo (this) ;
MyMemo1->Parent = (this) ;
不容易啊！

[huzhangyou]

呵呵
learning.............................................