iOS 代理 重定向消息 forwardInvocation

@interface NSInvocation : NSObject {
@private
    __strong void *_frame;
    __strong void *_retdata;
    id _signature;
    id _container;
    uint8_t _retainedArgs;
    uint8_t _reserved[15];
}

+ (NSInvocation *)invocationWithMethodSignature:(NSMethodSignature *)sig;

- (NSMethodSignature *)methodSignature;

- (void)retainArguments;
- (BOOL)argumentsRetained;

- (id)target;
- (void)setTarget:(id)target;

- (SEL)selector;
- (void)setSelector:(SEL)selector;

- (void)getReturnValue:(void *)retLoc;
- (void)setReturnValue:(void *)retLoc;

- (void)getArgument:(void *)argumentLocation atIndex:(NSInteger)idx;
- (void)setArgument:(void *)argumentLocation atIndex:(NSInteger)idx;

- (void)invoke;
- (void)invokeWithTarget:(id)target;

@end

NS_ROOT_CLASS
@interface NSProxy <NSObject> {
    Class    isa;
}

+ (id)alloc;
+ (id)allocWithZone:(NSZone *)zone NS_AUTOMATED_REFCOUNT_UNAVAILABLE;
+ (Class)class;

- (void)forwardInvocation:(NSInvocation *)invocation;
- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel;
- (void)dealloc;
- (void)finalize;
- (NSString *)description;
- (NSString *)debugDescription;
+ (BOOL)respondsToSelector:(SEL)aSelector;

- (BOOL)allowsWeakReference NS_UNAVAILABLE;
- (BOOL)retainWeakReference NS_UNAVAILABLE;

// - (id)forwardingTargetForSelector:(SEL)aSelector;

@end

#import <Foundation/Foundation.h>
#include <stdio.h>
 
 
@interface TargetProxy : NSProxy {
    id realObject1;
    id realObject2;
}
 
- (id)initWithTarget1:(id)t1 target2:(id)t2;
 
@end

@implementation TargetProxy
 
- (id)initWithTarget1:(id)t1 target2:(id)t2 {
    realObject1 = [t1 retain];
    realObject2 = [t2 retain];
    return self;
}
 
- (void)dealloc {
    [realObject1 release];
    [realObject2 release];
    [super dealloc];
}
 
// The compiler knows the types at the call site but unfortunately doesn‘t
// leave them around for us to use, so we must poke around and find the types
// so that the invocation can be initialized from the stack frame.
 
// Here, we ask the two real objects, realObject1 first, for their method
// signatures, since we‘ll be forwarding the message to one or the other
// of them in -forwardInvocation:.  If realObject1 returns a non-nil
// method signature, we use that, so in effect it has priority.
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
    NSMethodSignature *sig;
    sig = [realObject1 methodSignatureForSelector:aSelector];
    if (sig) return sig;
    sig = [realObject2 methodSignatureForSelector:aSelector];
    return sig;
}
 
// Invoke the invocation on whichever real object had a signature for it.
- (void)forwardInvocation:(NSInvocation *)invocation {
    id target = [realObject1 methodSignatureForSelector:[invocation selector]] ? realObject1 : realObject2;
    [invocation invokeWithTarget:target];
}
 
// Override some of NSProxy‘s implementations to forward them...
- (BOOL)respondsToSelector:(SEL)aSelector {
    if ([realObject1 respondsToSelector:aSelector]) return YES;
    if ([realObject2 respondsToSelector:aSelector]) return YES;
    return NO;
}

@end

int main(int argc, const char *argv[]) {
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    
    // Create an empty mutable string, which will be one of the
    // real objects for the proxy.
    NSMutableString *string = [[NSMutableString alloc] init];
 
    // Create an empty mutable array, which will be the other
    // real object for the proxy.
    NSMutableArray *array = [[NSMutableArray alloc] init];
 
    // Create a proxy to wrap the real objects.  This is rather
    // artificial for the purposes of this example -- you‘d rarely
    // have a single proxy covering two objects.  But it is possible.
    id proxy = [[TargetProxy alloc] initWithTarget1:string target2:array];
 
    // Note that we can‘t use appendFormat:, because vararg methods
    // cannot be forwarded!
    [proxy appendString:@"This "];
    [proxy appendString:@"is "];
    [proxy addObject:string];
    [proxy appendString:@"a "];
    [proxy appendString:@"test!"];
 
    NSLog(@"count should be 1, it is: %d", [proxy count]);
    
    if ([[proxy objectAtIndex:0] isEqualToString:@"This is a test!"]) {
        NSLog(@"Appending successful.", proxy);
    } else {
        NSLog(@"Appending failed, got: ‘%@‘", proxy);
    }
 
    NSLog(@"Example finished without errors.");
    [pool release];
    return 0;
}