Question

TBase = class(TObject)
...

TDerived = class(Tbase)
...

if myObject is TBase then ...

我可以以某种方式对此进行编码，如果myObject是TDerived类，它会返回false吗？

Answer 1

如果您需要精确的类类型检查，请使用ClassType方法：

type

TBase = class(TObject)
end;

TDerived = class(Tbase)
end;

procedure TForm1.Button1Click(Sender: TObject);
var
 A: TBase;

begin
  A:= TBase.Create;
  if A.ClassType = TBase then ShowMessage('TBase');  // shown
  A.Free;
  A:= TDerived.Create;
  if A.ClassType = TBase then ShowMessage('TBase again'); // not shown
  A.Free;
end;

Answer 2

您可以使用ClassType方法，或只检查Pointer（Object）^ = Class Type。

begin
  A:= TBase.Create;
  if A.ClassType = TBase then ShowMessage('TBase');  // shown
  if PPointer(A)^ = TBase then ShowMessage('TBase');  // shown
  A.Free;
  A:= TDerived.Create;
  if PPointer(A)^ = TBase then ShowMessage('TBase again'); // not shown
  if A.ClassType = TBase then ShowMessage('TBase again');  // not shown
  A.Free;
end;

如果您的代码在类方法中，则可以使用self来获取类值：

class function TBase.IsDerivedClass: boolean;
begin
  result := self=TDerivedClass;
end;

Answer 3

更好的方式;

type

TBase = class(TObject)
end;

TDerived = class(Tbase)
end;

procedure TForm1.Button1Click(Sender: TObject);
var
 A, B: TObject;

begin
  A:= TBase.Create;
  if A.ClassType = TBase then ShowMessage('A is Exacly TBase');  // shown
  if A is TBase then ShowMessage('A is TBase or SubClass of TBase');  // shown
  if A is TDerived then ShowMessage('A is TDerived or SubClass of TDerived ');  // NOT shown!! 
  A.Free;

  B:= TDerived.Create;
  if B.ClassType = TBase then ShowMessage('TBase again'); // not shown
  if B is TBase then ShowMessage('B is TBase or SubClass of TBase');  // shown
  if B is TDerived then ShowMessage('B is TDerived or SubClass of TDerived ');  // shown!! 
  B.Free;
end;

我如何使用“是”来检查或确切的类（不是后代）？

3 个答案: