我有这两个班：
type
TMyBaseClass = class
protected
FAllowDoSomething: Boolean; // initialized to False
procedure DoSomething; virtual;
end;
TMyChildClass = class(TMyBaseClass)
protected
procedure DoSomething; override;
end;
implementation
procedure TMyBaseClass.DoSomething;
begin
if not FAllowDoSomething then Exit; // Abort;
ShowMessage('TMyBaseClass: FAllowDoSomething is False. You wont see me!');
end;
procedure TMyChildClass.DoSomething;
begin
inherited; // Must inherit
// if not FAllowDoSomething then Exit; { I don't want to check here again }
ShowMessage('TMyChildClass: FAllowDoSomething is False but still I can see this message!');
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
with TMyBaseClass.Create do try
DoSomething;
finally
Free;
end;
// if I use Abort in TMyBaseClass,the code will not get here
with TMyChildClass.Create do try
DoSomething;
finally
Free;
end;
end;
在TMyChildClass.DoSomething中,我必须继承TMyBaseClass.DoSomething,但是我希望它遵守如果不是FAllowDoSomething然后<不做任何>.
我试过在TMyBaseClass中使用Abort,但是我意识到这不是一个好主意,并且会打破调用方法(TForm1.Button1Click);
解决方法
关键是在基类中对boolean执行一次检查.所以,使DoSomething非虚拟,并在您的基类中实现它,如下所示：
procedure TMyBaseClass.DoSomething;
begin
if FAllowDoSomething then
DoSomethingImplementation;
end;
其中DoSomethingImplementation是您在派生类中重写的虚拟方法.
基础类似如下：
type
TMyBaseClass = class
private
FAllowDoSomething: Boolean;
protected
procedure DoSomethingImplementation; virtual;
public
procedure DoSomething;
end;
你的派生类看起来像这样：
type
TMyDerivedClass = class(TMyBaseClass)
protected
procedure DoSomethingImplementation; override;
end;
您重写的方法如下所示：
procedure TMyDerivedClass.DoSomethingImplementation; begin inherited; ShowMessage(...); end;