又遇到繼承問題，父類有一字串，父類會填入資料，子類繼承父類，也會執行到填入該資料，
可是下次來看該資料卻變成空的！

測試程式：父類TfmBase與子類TfmChild，在MDI子視窗建立時會填入字串
換成 char cPower[20]; 就沒問題！
難道是vcl元件才會有此問題？？

希望先進能幫忙找到問題！感謝囉！




父類程式
[code cpp]
//---------------------------------------------------------------------------
class TfmBase : public TForm
{
__published: // IDE-managed Components
TTimer *Timer1;
TMemo *Memo1;
void __fastcall FormCreate(TObject *Sender);
void __fastcall Timer1Timer(TObject *Sender);
void __fastcall FormClose(TObject *Sender, TCloseAction &Action);
private: // User declarations
public: // User declarations
AnsiString sPower,sStartCompanyID,sEndCompanyID;
__fastcall TfmBase(TComponent* Owner);
};
//---------------------------------------------------------------------------
//---------------------------------------------------------------------------
//---------------------------------------------------------------------------
__fastcall TfmBase::TfmBase(TComponent* Owner)
: TForm(Owner)
{
Caption=Name;
}
//---------------------------------------------------------------------------
void __fastcall TfmBase::FormCreate(TObject *Sender)
{
sPower="1234567890";
if (sPower.IsEmpty()) {
Memo1->Lines->Add("空白！");
} else {
Memo1->Lines->Add(sPower);
}
}
//---------------------------------------------------------------------------
void __fastcall TfmBase::Timer1Timer(TObject *Sender)
{
if (sPower.IsEmpty()) {
Memo1->Lines->Add("空白！");
} else {
Memo1->Lines->Add(sPower);
}
}
//---------------------------------------------------------------------------
void __fastcall TfmBase::FormClose(TObject *Sender, TCloseAction &Action)
{
Action=caFree;
}
//---------------------------------------------------------------------------

[/code]

子類程式
[code cpp]
//---------------------------------------------------------------------------
class TfmChild : public TfmBase
{
__published: // IDE-managed Components
private: // User declarations
public: // User declarations
__fastcall TfmChild(TComponent* Owner);
};
//---------------------------------------------------------------------------
//---------------------------------------------------------------------------
//---------------------------------------------------------------------------
__fastcall TfmChild::TfmChild(TComponent* Owner)
: TfmBase(Owner)
{
}
//---------------------------------------------------------------------------
[/code]

主程式
[code cpp]
//---------------------------------------------------------------------------
class TfmMain : public TForm
{
__published: // IDE-managed Components
TPanel *Panel1;
TButton *btStart;
void __fastcall btStartClick(TObject *Sender);
private: // User declarations
public: // User declarations
__fastcall TfmMain(TComponent* Owner);
};
//---------------------------------------------------------------------------
//---------------------------------------------------------------------------
//---------------------------------------------------------------------------
__fastcall TfmMain::TfmMain(TComponent* Owner)
: TForm(Owner)
{
}
//---------------------------------------------------------------------------
void __fastcall TfmMain::btStartClick(TObject *Sender)
{
if (dynamic_cast(fmChild)==0) fmChild=new TfmChild(Application);
if (dynamic_cast(fmBase)==0) fmBase=new TfmBase(Application);
TileMode=tbVertical;
Tile();
}
//---------------------------------------------------------------------------
[/code]

------
>>>好心有好報

附加檔案：48d92c5b4be98_Test.jpg

編輯記錄

根據我的了解與trace debug發現，在bcb中的物件初始化的順序與一般的ｃ++不同。

vcl因為是delphi寫的，所以他的建構方式是由子到父的方向。而c 是由父到子。

而create的這個event也因為是配合delphi而用，故在bcb中要特別注意。看help檔中的一段話:
Use of the OnCreate event is discouraged in C Builder because it can interact badly with the form constructor (see OldCreateOrder). It is recommended that you override the form constructor instead. (ps事實上改order也是無效的)

經過實際的追蹤，建構順序如下。TfmChild( ) --> TfmBase( ) -->TForm( ) -->TCustomForm( ) --> .......-->TfmBase::FormCreate( ) -->三個你的自定AnsiString被建構-->Caption=Name;

注意最後面的那三個過程! 在oncreate時sPower被建構且給值了，但之後sPower,sStartCompanyID,sEndCompanyID;三個值被建構。於是sPower的Data又空了。

建議你把sPower="1234567890";放於TfmBase::TfmBase( )建構式裡就不會有問題。因為它比oncreate還要更後面才執行。

當然，若你用的是char[ ] ，則沒有建構的問題，故值會一直被保持著。

------


蕭沖
--All ideas are worthless unless implemented--

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編輯記錄