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我想使用 TOwnedCollection / TCollectionItem 实现一个集合或列表。我需要一个具有多态性的类的持久列表（从 FileStream 加载和创建）。

到目前为止，这是我的（部分）代码，但我没有成功创建派生类 TGenerator 而不是其父类 TPowerComponent 并将其添加到集合中。

//-------------------------------------------------------------------------------------
class TPCCollection : public TOwnedCollection
    {
            typedef TOwnedCollection inherited;
    private:
            TPowerComponent* __fastcall GetPowerComponent(int Index);
            void __fastcall SetPowerComponent(int Index, TPowerComponent *Value);

    public:
            __fastcall TPCCollection(TPersistent *Owner);

            HIDESBASE TPowerComponent* __fastcall Add(void);
            HIDESBASE TPowerComponent* __fastcall Insert(int Index);

            __property TPowerComponent* PCCollection[int Index] = {read=GetPowerComponent, write=SetPowerComponent};
};

//-------------------------------------------------------------------------------------
class TPowerComponent : public TCollectionItem
{
    typedef TCollectionItem inherited;
public :
    int X, Y, Rotation;
    PowSymbType HisType;

    __fastcall TPowerComponent(TCollection *Collection, PowSymbType AType );
    void __fastcall Assign(TPersistent *Source);
    virtual void __fastcall Paint(TCanvas * Canvas);
};
//-------------------------------------------------------------------------------------
class TGenerator : public TPowerComponent
{
            typedef TPowerComponent inherited;
public :
    double PG, Qgmin, Qgmax, Vsch;

    __fastcall TGenerator(TCollection *Collection, PowSymbType AType );
    void __fastcall Assign(TPersistent *Source);
    virtual void __fastcall Paint(TCanvas * Canvas);    
    };
//-------------------------------------------------------------------------------------
// implementation
//-------------------------------------------------------------------------------------
//  TPCCOllection
//-------------------------------------------------------------------------------------
__fastcall TPCCollection::TPCCollection(TPersistent *Owner)
        : TOwnedCollection(Owner, __classid(TPowerComponent))
{
}
//-------------------------------------------------------------------------------------
TPowerComponent* __fastcall TPCCollection::Add()
{
    return static_cast<TPowerComponent>(inherited::Add());
}
//-------------------------------------------------------------------------------------
TPowerComponent* __fastcall TPCCollection::Insert(int Index)
{
    return static_cast<TPowerComponent>(inherited::Insert(Index));
}
//-------------------------------------------------------------------------------------
TPowerComponent* __fastcall TPCCollection::GetPowerComponent(int Index)
{
    return static_cast<TPowerComponent>(inherited::GetItem(Index));
}
//-------------------------------------------------------------------------------------
void __fastcall TPCCollection::SetPowerComponent(int Index, TPowerComponent *Value)
{
    inherited::SetItem(Index, Value);
}
//-------------------------------------------------------------------------------------
//  TPowerComponent
//-------------------------------------------------------------------------------------
__fastcall TPowerComponent::TPowerComponent(TCollection *Collection, PowSymbType AType )
        : TCollectionItem(Collection)
{
    HisType=AType;
    Rotation=0;
}
//-------------------------------------------------------------------------------------
void __fastcall TPowerComponent::Assign(TPersistent *Source)
{
    TPowerComponent *Src = dynamic_cast<TPowerComponent>(Source);
    if( Src )
        {
                // copy members from Src...
        }
    else    inherited::Assign(Source);
}
//-------------------------------------------------------------------------------------
// se dessine
void __fastcall TPowerComponent::Paint(TCanvas * Canvas)
{
...
}
//-------------------------------------------------------------------------------------
//  TGenerator
//-------------------------------------------------------------------------------------
__fastcall TGenerator::TGenerator(TCollection *Collection, PowSymbType AType )
        :TPowerComponent( Collection, AType )
{
    PG=0; Qgmin=0; Qgmax=0; Vsch=1.0; Con=-1;
}
//-------------------------------------------------------------------------------------
void __fastcall TGenerator::Assign(TPersistent *Source)
{
    TGenerator *Src = dynamic_cast<TGenerator>(Source);
    if( Src )
        {
                // copy members from Src...
        }
    else    inherited::Assign(Source);
}



//-------------------------------------------------------------------------------------
//  Usage 
TPCCollection * NetWork = new TPCCollection(this);

//  Usage to Access all the collection
for( int i=0; i< NetWork->Count; i++)
    {
    ((TPowerComponent*)(NetWork->Items[i]))->Paint(Canvas);
    }

要添加 TGenerator 而不是 TPowerComponent，我使用：

TGenerator * Gen=new TGenerator( NetWork, Generator);

TCollectionItem 子项的创建自动将自身添加到 TCollection

这里的问题是我们无法将创建项目的过程与将其添加到集合中分开。

例如，当我需要另一个可以包含第一个集合列表的某些项目的列表时，SelectedComponents 可以包含网络集合的一个或一些项目，而无需重新创建它们。

这可以通过

std::list<TPowerComponent*> SelectedComponents;

但我无法使用 FileStream / 持久列表来写入/读取它们。我需要将它们放在 TCollection 中，但不重新创建它们。

如何？

4

1 回答 1

1

The RTL's native DFM streaming for TCollection objects only partially supports polymorphic TCollectionItem classes.

You can add polymorphic TCollectionItem objects to a TCollection in code (at runtime, as well as at design-time with the aid of a custom editor), as long as they all derive from a common base class that is passed to the TCollection constructor. And such a collection can even be saved as-is to a DFM.

However, when loading back a DFM, native streaming will force all collection items read from the DFM to use whatever TCollectionItem class type you pass to the TCollection constructor. So, polymorphic classes can't be loaded natively.

The only way to override that behavior is to disable native streaming for the collection (make your TCollection property be non-published, or at least mark it as stored=false), and then stream the collection items manually.

Have your main component (or whatever TPersistent class owns the collection) override the virtual DefineProperties() method to call TFiler.DefineProperty() to register custom reading/writing methods for streaming the collection items. To support polymorphic classes, you will have to write each item's ClassName to the DFM before writing its property values, then read the name back so you know which class to instantiate before then reading property values.

于 2018-01-04T20:41:06.263 回答