10. Ios-runtime Preliminary study of message forwarding process

tip

I want to know what methods are inserted into the cache

Here you want to open the hidden folder display Shift + Command +.

What did you do when you started studying this approach

Let’s see if this works

1. Create a class that declares an unimplemented method

2. Implement this method in a.m file.

- (id)forwardingTargetForSelector:(SEL)aSelector{
    NSLog(@"%s - %@",__func__,NSStringFromSelector(aSelector));
    return nil;
}

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3. This method is called even though the result is an error

4. Now create another class and implement this method.

5. Import this class and return the value of this method as a new object

6. The result is a successful implementation of another class method call

OC calls the method through sel-> IMP
- 1. Objc_msgSend searches the cache
- 2. Search methodList slowly
- 3. Dynamic method resolution
- 4. The Runtime mechanism lets other classes call methods with the same method name to do this.

Fast forward

// Fast forward
- (id)forwardingTargetForSelector:(SEL)aSelector{
    NSLog(@"%s - %@",__func__,NSStringFromSelector(aSelector));
    return nil;
}

- (id)forwardingTargetForSelector:(SEL)aSelector{
    return [LGStudent alloc];
}
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Add that the class we return does not have an implementation of this method, so slow forwarding is requiredmethodSignatureForSelectorMethods withforwardInvocationuse

Slowly forward

//// Slow forwarding
// Return a method signature
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector{
    NSLog(@"%s - %@",__func__,NSStringFromSelector(aSelector));
    if (aSelector == @selector(sayHello)) {
        // Return a method signature
        return [NSMethodSignature signatureWithObjCTypes:"v@:@"];
    }
    return [super methodSignatureForSelector:aSelector];
}
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This method is not implemented for the time being

- (void)forwardInvocation:(NSInvocation *)anInvocation{
    NSLog(@ % @ - % @ "",anInvocation.target,NSStringFromSelector(anInvocation.selector));
}
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Found that the program did not crash while logging the method called by the object. This can be used as a collection of error logs.

Here tip us if this method to implement will need to rewrite methodSignatureForSelector

- (void)forwardInvocation:(NSInvocation *)anInvocation{
// NSLog(@"%@ - %@",anInvocation.target,NSStringFromSelector(anInvocation.selector));
    LGStudent *s = [LGStudent alloc];
    // Determine that self can handle this method
    if ([self respondsToSelector:anInvocation.selector]) {
        [anInvocation invoke]; // Invoke directly
    }else if ([s respondsToSelector:anInvocation.selector]){
        // Determine which class can handle this method
        [anInvocation invokeWithTarget:s];
    }else{
        // There is a crash
        NSLog(@"%s - %@",__func__,NSStringFromSelector(anInvocation.selector)); }}Copy the code