如何检查接口对象是否实现另一个接口？

Question

我有这些接口声明：

IListener = interface 
    procedure HandleEvent(AEvent: TMyEvent); 
end; 

IExtendedListener = interface(IListener) 
    ['{85A3456A-D5E5-4F37-ABDD-A75A7B3B494C}'] // required by GetInterface 
    procedure HandleExtendedEvent(AExtendedEvent: TMyExtendedEvent); 
end; 

考虑的东西，实现IListener接口引用，我怎么能检查是否还实现IExtendedListener？我正在使用下面的代码代码，因为编译时错误做了类似if Listener is IExtendedListener then ...。

TSomeClass.Notify(AEvent: TMyExtendedEvent); 
var 
    Listener: IListener; 
    ExtListener: IExtendedListener; 
    Obj: TObject; 
begin 
    for Listener in FListeners do 
    begin 
    // works but smells funny 
    Obj := Listener as TObject; 
    Obj.GetInterface(IExtendedListener, ExtListener); 
    if Assigned(ExtListener) then 
     ExtNotifyee.HandleExtendedEvent(AEvent); 
    end; 
end; 

Answer 1

您应该使用Sysutils.Supports，检查是否有特殊的接口

uses 
    SysUtils; 

TSomeClass.Notify(AEvent: TMyExtendedEvent); 
var 
    Listener : IListener; 
    ExtListener : IExtendedListener; 
begin 
    for Listener in FListeners do 
    if Supports(Listener, IExtendedListener, ExtListener) then 
     ExtListener.HandleExtendedEvent(AEvent); 
end;