因為需要去取到該元件的Caption
各個元件的寫法其實都一樣
( (TLabel *)Form->Components[i])->Caption)
or
( (TButton *)Form->Components[i])->Caption)

所以想找個方法 可以概括大部分的情形
經過在討論區搜尋相關的問題，
有篇文章是有關取元件的WIdth
http://delphi.ktop.com.tw/board.php?cid=168&fid=913&tid=72083
他的寫法是
Obj)}
[/code]


經過搜尋過BCB目錄下 "dynamic_cast"
所得到的結果都是 dynamic_cast(ptr)
若是寫成 dynamic(Form->Components[i])->Caption
那就與我目前的寫法相同，達不到簡潔的目的

想請問在BCB6的環境下是否真的可以使用 dynamic_cast(Sender)這樣的語法
或是有其他應注意而我未注意之處還請指教

謝謝各位先進！

醬樣子呢!!
(dynamic_cast(Sender))->Caption;


===================引 用 BIMEGiGio 文 章===================
因為需要去取到該元件的Caption
各個元件的寫法其實都一樣
( (TLabel *)Form->Components[i])->Caption)
or
( (TButton *)Form->Components[i])->Caption)

所以想找個方法 可以概括大部分的情形
經過在討論區搜尋相關的問題，
有篇文章是有關取元件的WIdth
http://delphi.ktop.com.tw/board.php?cid=168&fid=913&tid=72083
他的寫法是
Obj)}
[/code]


經過搜尋過BCB目錄下 "dynamic_cast"
所得到的結果都是 dynamic_cast(ptr)
若是寫成 dynamic(Form->Components[i])->Caption
那就與我目前的寫法相同，達不到簡潔的目的

想請問在BCB6的環境下是否真的可以使用 dynamic_cast(Sender)這樣的語法
或是有其他應注意而我未注意之處還請指教

謝謝各位先進！

dynamic_cast

Category
C -Specific Keywords
Description
In the expression, dynamic_cast< T > (ptr), T must be a pointer or a reference to a defined class type or void*. The argument ptr must be an expression that resolves to a pointer or reference.
If T is void* then ptr must also be a pointer. In this case, the resulting pointer can access any element of the class that is the most derived element in the hierarchy. Such a class cannot be a base for any other class.
Conversions from a derived class to a base class, or from one derived class to another, are as follows: if T is a pointer and ptr is a pointer to a non-base class that is an element of a class hierarchy, the result is a pointer to the unique subclass. References are treated similarly. If T is a reference and ptr is a reference to a non-base class, the result is a reference to the unique subclass.
A conversion from a base class to a derived class can be performed only if the base is a polymorphic type.
The conversion to a base class is resolved at compile time. A conversion from a base class to a derived class, or a conversion across a hierarchy is resolved at runtime.
If successful, dynamic_cast< T > (ptr) converts ptr to the desired type. If a pointer cast fails, the returned pointer is valued 0. If a cast to a reference type fails, the Bad_cast exception is thrown.
Note: Runtime type identification (RTTI) is required for dynamic_cast.



//---------------------------------------------------------------------------------------------------------------------------------------------------------------------------
// HOW TO MAKE DYNAMIC CASTS
// This program must be compiled with the -RT (Generate RTTI) option.
#include
#include
class Base1
{
// In order for the RTTI mechanism to function correctly,
// a base class must be polymorphic.
virtual void f(void) { /* A virtual function makes the class polymorphic */ }
};
class Base2 { };
class Derived : public Base1, public Base2 { };
int main(void) {
try {
Derived d, *pd;
Base1 *b1 = &d;
// Perform a downcast from a Base1 to a Derived.
if ((pd = dynamic_cast(b1)) != 0) {
std::cout << "The resulting pointer is of type "
<< typeid(pd).name() << std::endl;
}
else throw Bad_cast();
// Attempt cast across the hierarchy. That is, cast from
// the first base to the most derived class and then back
// to another accessible base.
Base2 *b2;
if ((b2 = dynamic_cast<Base2 *>(b1)) != 0) {
cout << "The resulting pointer is of type "
<< typeid(b2).name() << endl;
}
else throw Bad_cast();
}
catch (Bad_cast) {
cout << "dynamic_cast failed" << endl;
return 1;
}
catch (...) {
cout << "Exception handling error." << endl;
return 1;
}
return 0;
}

僅供參考....


[code cpp]
//---------------------------------------------------------------------------
#ifndef fMainH
#define fMainH
//---------------------------------------------------------------------------
#include
#include
#include
#include <Forms.hpp><br />//---------------------------------------------------------------------------
class TfrmMain : public TForm
{
__published:
TButton *Button1;
TButton *Button2;
void __fastcall Button1Click(TObject *Sender);
void __fastcall Button2Click(TObject *Sender);
private:
void __fastcall SHOW_COMPONENT_INFO(TObject *O);
int __fastcall TEST_WIDTH(TObject *O);
public:
__fastcall TfrmMain(TComponent* Owner);
};
//---------------------------------------------------------------------------
extern PACKAGE TfrmMain *frmMain;
//---------------------------------------------------------------------------
#endif
[/code]


[code cpp]
//---------------------------------------------------------------------------
#include
#pragma hdrstop
#include "fMain.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TfrmMain *frmMain;
//---------------------------------------------------------------------------
__fastcall TfrmMain::TfrmMain(TComponent* Owner): TForm(Owner)
{
}
//---------------------------------------------------------------------------
void __fastcall TfrmMain::SHOW_COMPONENT_INFO(TObject *O)
{
String S;
if(O->ClassNameIs("TLabel"))
S = (dynamic_cast(O))->Caption;
else if(O->ClassNameIs("TEdit"))
S = (dynamic_cast(O))->Text;
else
S = "Unknown Component: " O->ClassName();
ShowMessage(S);
}
//---------------------------------------------------------------------------
int __fastcall TfrmMain::TEST_WIDTH(TObject *O)
{
//先想想: Width 屬性是在 TControl 下被定義出來的, 所以
if(O->InheritsFrom(__classid(TControl)))
return (dynamic_cast(O))->Width;
else
return -1;
}
//---------------------------------------------------------------------------
void __fastcall TfrmMain::Button1Click(TObject *Sender)
{
TLabel *L = new TLabel(this);
try{
L->Caption = "I am a TLabel.";
SHOW_COMPONENT_INFO(L);
L->Width = 99;
ShowMessage(TEST_WIDTH(L));
}
__finally{
delete L;
}
}
//---------------------------------------------------------------------------
void __fastcall TfrmMain::Button2Click(TObject *Sender)
{
TEdit *E = new TEdit(this);
try{
E->Text = "I am a TEdit.";
SHOW_COMPONENT_INFO(E);
E->Width = 88;
ShowMessage(TEST_WIDTH(E));
}
__finally{
delete E;
}
}
//---------------------------------------------------------------------------
[/code]

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