如何创建自定义组件？ 访问私有字段时出错

Question

I want to create a new component derived from TPanel. This new component has only one private field: "obj" (a TObject).
In the constructor I create the object. Later, when I try to access the object it is NULL. Why?

Header:

class PACKAGE TMyClass : public TPanel
{
private:
    TObject *obj;
protected:
public:
   __fastcall TMyClass(TComponent* Owner);
   void Stuff();
};

CPP file:

__fastcall TMyClass::TMyClass(TComponent* Owner)
   : TPanel(Owner)
{
    Caption        = "";
    DoubleBuffered = True;
    Width          = 385;
    Height         = 65;

    TObject *obj= new TObject;     //obj gets an address here
}



void TMyClass::Stuff()      // <---- I call this method in the OnClick event of a button.
{
   Caption = obj->ClassName();    //obj is NULL here
}
//---------------------------------------------------------------------------








namespace Uvolctrl
{ void __fastcall PACKAGE Register()
   {  TComponentClass classes[1] = {__classid(TMyClass)};
       RegisterComponents(L"Samples", classes, 0); } }



static inline void ValidCtrCheck(TMyClass *)   // assure that the components do not have any pure virtual functions.
{ new TMyClass(NULL);    }

Answer 1

在构造函数中，您正在创建一个类实例，并将其分配给名为obj的局部变量，而不是您的私有obj成员变量。