如何以正确的方式实施授权？

Question

我正在尝试为一个应该调用它的委托(如果有的话)的类实现委托,当特殊事情发生时.

从维基百科我有这个代码示例:

 @implementation TCScrollView
 -(void)scrollToPoint:(NSPoint)to;
 {
   BOOL shouldScroll = YES;
   // If we have a delegate, and that delegate indeed does implement our delegate method,
   if(delegate && [delegate respondsToSelector:@selector(scrollView:shouldScrollToPoint:)])
     shouldScroll = [delegate scrollView:self shouldScrollToPoint:to]; // ask it if it's okay to scroll to this point.

   if(!shouldScroll) return;  // If not, ignore the scroll request.

   /// Scrolling code omitted.
 }
 @end

如果我自己尝试这个,我会收到一个警告,说我找不到我在代理上调用的方法.当然不是,因为委托只是由id引用.它可能是任何东西.当然在运行时会工作正常,因为我检查它是否响应选择器.但我不想在Xcode中发出警告.有更好的模式吗？

Answer 1

您可以让委托者具有实现SomeClassDelegate协议的id类型.为此,您可以在SomeClass的标题中(在您的情况下为TCScrollView),执行以下操作:

@protocol TCScrollViewDelegate; // forward declaration of the protocol

@interface TCScrollView {
    // ...
    id <TCScrollViewDelegate> delegate;
}
@property (assign) id<TCScrollViewDelegate> delegate;
@end

@protocol TCScrollViewDelegate
- (BOOL) scrollView:(TCScrollView *)tcScrollView shouldScrollToPoint:(CGPoint)to;
@end

然后你可以从你的实现中,只需调用委托上的方法:

@implementation TCScrollView

-(void)scrollToPoint:(NSPoint)to;
{
  BOOL shouldScroll = YES;
  shouldScroll = [delegate scrollView:self shouldScrollToPoint:to]; // ask it if it's okay to scroll to this point.
  if(!shouldScroll) return;  // If not, ignore the scroll request.
  /// Scrolling code omitted.
}
@end