runtime浅谈（三）消息转发

来源：互联网发布：天干地支最简单的算法编辑：程序博客网时间：2024/06/06 08:45

看了一下文章也进行了一些测试，关于消息转发做一小节。

<span style="font-size:14px;">- (id)forwardingTargetForSelector:(SEL)aSelector;- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector;+ (NSMethodSignature *)instanceMethodSignatureForSelector:(SEL)aSelector;- (void)forwardInvocation:(NSInvocation *)anInvocation;- (void)doesNotRecognizeSelector:(SEL)aSelector;</span>

调用方法：

[someObj method1];//方式1[someObj performSelector:@selector(method1)];//方式2

如果 SomeObj没有实现 method1函数

runtime 将会调用

<span style="font-size:14px;">- (id)forwardingTargetForSelector:(SEL)aSelector{    if ([SomeObj respondsToSelector:aSelector]) {        return SomeObj;    }       return nil;}</span>

如果 SomeObj 能够响应 aSelector,我们就将此消息转发到 SomeObj.

如果SomeObj 不能响应,函数返回了 nil

此时 runtime system将调用

<span style="font-size:14px;">- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector{    NSMethodSignature *signature = [super methodSignatureForSelector:aSelector];    if (signature == nil) {        signature = [OtherObj instanceMethodSignatureForSelector:aSelector];    }         return signature;</span><pre name="code" class="objc"><span style="font-size:14px;">}</span>

如果父类没有实现此SEL,就询问 OtherObj 是否实现此 SEL

如果实现就返回NSMethodSignature

否则就返回 nil,此时 runtime system就会调用

<span style="font-size:14px;">- (void)doesNotRecognizeSelector:(SEL)aSelector{    NSLog(@"%@ %@",NSStringFromClass(self.class),NSStringFromSelector(_cmd));}</span><span style="font-size: 11px;"></span>

表示没有实现此函数,并抛出NSInvalidArgumentException 异常

可以在此函数中做程序最后的处理

说回去,如果OtherObj实现了此函数,则 runtime system 会调用

<span style="font-size:14px;">- (void)forwardInvocation:(NSInvocation *)anInvocation{    if ([OtherObj instancesRespondToSelector:[anInvocation selector]])        [anInvocation invokeWithTarget:otherObj];    else        [super forwardInvocation:anInvocation];}</span>

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