我创建了一个包装UITextView并添加一些ui元素的类.我希望新类’API与UITextView相同,因此我使用消息转发(下面列出)在包装文本视图和委托之间中继消息.
令人恼火的是,编译器会在转发类的实例上发出方法调用警告.例如,将为以下行生成错误：
[aMyTextView setContentOffset:CGPointZero animated:YES];
所以我被迫为这些方法声明并创建“手动转发”实现,这违背了使用消息转发的整个目的.
- (void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated
{
[_textView setContentOffset:contentOffset animated:animated];
}
我知道解决这个问题的通常方法是使用performSelector：方法之一,但这是一个麻烦的,当一些参数不是NSObjects时(虽然Erica Sadun’s extensions是一个很大的帮助),b)再次,完全违背了创建一个透明的包装器.
(子类化UITextView也是不可能的,因为我需要在文本视图下面插入视图.)
有办法解决这个问题吗？
列出该类的所有相关部分：
@interface MyTextField : UIView<UITextViewDelegate>
{
UIImageView* _border;
UITextView* _textView;
UIButton* _clearButton;
NSObject<UITextViewDelegate>* _delegate;
}
@implementation MWTextField
. . .
// Forwards messages in both directions (textView <--> delegate)
#pragma mark Message forwarding
// Protocol messages will only be sent if respondsToSelector: returns YES
- (BOOL)respondsToSelector:(SEL)aSelector
{
if ([_delegate respondsToSelector:aSelector])
return YES;
else
return [super respondsToSelector:aSelector];
}
- (NSMethodSignature *)methodSignatureForSelector:(SEL)selector
{
// First,try to find it in the UITextView
if ([_textView respondsToSelector:selector])
{
return [_textView methodSignatureForSelector:selector];
}
// Then try the delegate
else if ([_delegate respondsToSelector:selector])
{
return [_delegate methodSignatureForSelector:selector];
}
else
{
return [super methodSignatureForSelector: selector];
}
}
- (void)forwardInvocation:(NSInvocation *)invocation
{
SEL aSelector = [invocation selector];
if ([_textView respondsToSelector:aSelector])
{
[invocation invokeWithTarget:_textView];
}
else if ([_delegate respondsToSelector:aSelector])
{
[invocation invokeWithTarget:_delegate];
}
else
{
[self doesNotRecognizeSelector:aSelector];
}
}
. . .
@end
解决方法
声明一个类别,该类别提供您要转发的方法的方法声明：
@interface MyTextField (ImGonnaLetYouFinishButFirstImForwardingThese) ... methods you want to forward here ... @end
无需提供@implementation.
请注意,这是一种相当不典型的模式.不公平,非常.应该没有理由不能进行子类化.你说Subclassing UITextView也是不可能的,因为我需要在文本视图下面插入视图,但事实并非如此.
If I subclass UITextField,all I can
do with the other views is to add them
as subviews,which means they will be
on top of the text field. I guess I
could modify drawRect:… Is that what
you would suggest? Or what do you have
up your sleeve there?
如果需要组,请创建一个UIView子类,该子类适当地管理各种子视图,不需要转发.然后你可以随意订购视图.
很少使用转发.沿着这条路走下去就是疯狂.这听起来好像你的设计有点杂草,但没有足够的信息来真正说出更具体的信息.