可變類創建

Question

我想利用可變類類型，以儘量減少此代碼，它是從屬性和事件：

if ctype='T' then 
begin 
    C:= TTimeEdit.Create(self); 
    (c as TTimeEdit).OnMouseUp:= Panel2MouseUp; 
    (c as TTimeEdit).OnMouseDown:= Panel2MouseDown; 
    (c as TTimeEdit).OnMouseMove:= Panel2MouseMove; 
    (c as TTimeEdit).PopupMenu:= PopupMenu1; 
end; 

if ctype='S' then 
begin 
    C:= TTabSheet.Create(self); 
    (c as TTabSheet).OnMouseUp:= Panel2MouseUp; 
    (c as TTabSheet).OnMouseDown:= Panel2MouseDown; 
    (c as TTabSheet).OnMouseMove:= Panel2MouseMove; 
    (c as TTabSheet).PopupMenu:= PopupMenu1; 
end; 

看起來像這樣：

VAR VARCLS:TCLASS; 
BEGIN 
    if ctype='S' then 
    VARCLS:=TTabSheet; 
    if ctype='T' then 
    VARCLS:=TTimeEdit; 
    C:= VARCLS.Create(self); 
    (c as VARCLS).OnMouseUp:= Panel2MouseUp; 
    (c as VARCLS).OnMouseDown:= Panel2MouseDown; 
    (c as VARCLS).OnMouseMove:= Panel2MouseMove; 
    (c as VARCLS).PopupMenu:= PopupMenu1; 
end; 

確保代碼要長得多比這個，但我用了一個樣本！

Answer 1

有兩種方法可以做到這一點：

如果類有一個共同的祖先（很可能爲VCL或FMX類），那麼你可以只使用一個class of TAncestor並創建該類的一個特定實例。

參見：http://docwiki.embarcadero.com/RADStudio/Seattle/en/Class_References#Constructors_and_Class_References

假設你正在使用VCL，它幾乎是用FMX 有一個警告的TControl事件受到保護一樣，但我們可以用一箇中介類要解決這個問題。

type 
    TMyClass = class of TControl; 

//interposer class, makes events public; 

TPublicControl = class(TControl) 
public 
    property OnMouseUp;  //a 'naked' property redeclares the existing 
    property OnMouseDown; //events and properties as public 
    property OnMouseMove; 
    property PopupMenu; 
end; 

function CreateThing(Owner: TControl; MyType: TMyClass): TControl; 
begin 
    Result:= MyType.Create(Owner); 
    TPublicControl(Result).OnMouseUp:= Panel2MouseUp; 
    .... 
end; 

該例程不必知道類型，仍然返回一個特定的創建實例。

你調用這個例程，像這樣：

var 
    MyEdit: TEdit; 
begin 
    MyEdit:= TEdit(CreateThing(Panel, TEdit)); 

另一種方法是使用RTTI，但我不會推薦，除非你使用的是沒有一個共同的祖先對象。
如果您確實如此，請告訴我，我會擴大答案。