得到此警告初始化类型＆＃39; id＆＃39;

Question

    - (id) firstResponder: (UIView *) navView {
            for (id aview in [self allSubviews:navView]) {
                if ([aview isKindOfClass:[UITextField class]] && [(UITextField *)aview isFirstResponder]) {
                    return (UITextField *)aview;
            }
            else if ([aview isKindOfClass:[UITextView class]] && [(UITextView *)aview isFirstResponder]) {
                return (UITextView *)aview;
            }
        }
        return NO;
    }

收到错误：从iOS 8中的常量布尔表达式初始化类型'id'的指针为null。

Answer 1

变化：

return NO;

为：

return nil;

（NO是一个布尔文字，编译器抱怨它被转换为类型id以便返回。）

Answer 2

如何更改实现如下...

在此，您无需担心NO，nil，null等，即使编译器不会警告id或integer

- (id) firstResponder: (UIView *) navView {
    UIView *view = nil;
    for (id aview in [self allSubviews:navView]) {
        if ([aview isKindOfClass:[UITextField class]] && [(UITextField *)aview isFirstResponder]) {
            view = (UITextField *)aview;
        }
        else if ([aview isKindOfClass:[UITextView class]] && [(UITextView *)aview isFirstResponder]) {
            view = (UITextView *)aview;
        }
    }
    return view;
}