[crash详解与预防] unrecognized selector crash

//  缺失的selector是实例方法调用
+(BOOL)resolveInstanceMethod:(SEL)selector
//  缺失的selector是类方法调用
+(BOOL)resolveClassMethod:(SEL)selector

-(id)forwardingTargetForSelector:(SEL)selector

-(void)forwardInvocation:(NSInvocation*)invocation

//EOCAutoDictionary.h
@interface EOCAutoDictionary : NSObject
@property(nonatomic, strong) NSDate *date;
@end

//EOCAutoDictionary.m
#import "EOCAutoDictionary.h"
#import <objc/runtime.h>

@interface EOCAutoDictionary()
@property(nonatomic, strong) NSMutableDictionary *backingStore;
@end

@implementation EOCAutoDictionary

@dynamic date;

- (id)init {
    if(self = [super init]) {
        _backingStore = [NSMutableDictionary new];
    }
    return self;
}

+ (BOOL) resolveInstanceMethod:(SEL)selector {
    //selector = "setDate:" 或 "date",_cmd = (SEL)"resolveInstanceMethod:"
    NSString *selectorString = NSStringFromSelector(selector);
    if([selectorString hasPrefix:@"set"]) {
        // 向类中动态的添加方法，第三个参数为函数指针，指向待添加的方法。最后一个参数表示待添加方法的“类型编码”
        class_addMethod(self, selector,(IMP)autoDictionarySetter,"v@:@");
    } else {
        class_addMethod(self, selector,(IMP)autoDictionaryGetter,"v@:@");
    }
    return YES;
}

id autoDictionaryGetter(id self, SEL _cmd) {
    
    // 此时_cmd = (SEL)"date"
    
    // Get the backing store from the object
    EOCAutoDictionary *typeSelf = (EOCAutoDictionary *) self;
    NSMutableDictionary *backingStore = typeSelf.backingStore;
    
    //the key is simply the selector name
    NSString *key = NSStringFromSelector(_cmd);
    
    //Return the value
    return [backingStore objectForKey:key];
}

void autoDictionarySetter(id self, SEL _cmd, id value) {
    
    // 此时_cmd = (SEL)"setDate："
    // Get the backing store from the object
    EOCAutoDictionary *typeSelf = (EOCAutoDictionary *) self;
    NSMutableDictionary *backingStore = typeSelf.backingStore;
    
    /** The selector will be for example, "setDate:".
     * We need to remove the "set",":" and lowercase the first letter of the remainder.
     */
    NSString *selectorString = NSStringFromSelector(_cmd);
    NSMutableString *key = [selectorString mutableCopy];
    
    // Remove the ‘:‘ at the end
    [key deleteCharactersInRange:NSMakeRange(key.length-1, 1)];
    
    // Remove the ‘set‘ prefix
    [key deleteCharactersInRange:NSMakeRange(0, 3)];
    
    // Lowercase the first character
    NSString *lowercaseFirstChar = [[key substringToIndex:1] lowercaseString];
    [key replaceCharactersInRange:NSMakeRange(0, 1) withString:lowercaseFirstChar];
    
    if(value) {
        [backingStore setObject:value forKey:key];
    } else {
        [backingStore removeObjectForKey:key];
    }
}
@end

EOCAutoDictionary *dict = [EOCAutoDictionary new];
dict.date = [NSDate dateWithTimeIntervalSince1970:475372800];
NSLog(@"dict.date = %@", dict.date);

@implementation SLVForwardTarget
#pragma mark forwardingTargetForSelector
-(id) forwardingTargetForSelector:(SEL)aSelector {
    if(aSelector == @selector(uppercaseString)){
        return @"hello WorLD!";
    }
    return nil;
}
@end

SLVForwardTarget *ft = [SLVForwardTarget new];
NSString * s = [ft performSelector:@selector(uppercaseString)];
NSLog(@"%@",s);
//输出结果为：“HELLO WORLD!”

// SLVForwardInvocation.h
@interface SLVForwardInvocation : NSObject
- (id)initWithTarget1:(id)t1 target2:(id)t2;
@end

// SLVForwardInvocation.m
@interface SLVForwardInvocation()
@property(nonatomic, strong)id realObject1;
@property(nonatomic, strong)id realObject2;
@end

@implementation SLVForwardInvocation

- (id)initWithTarget1:(id)t1 target2:(id)t2 {
    _realObject1 = t1;
    _realObject2 = t2;
    return self;
}

//系统check实例是否能response消息呢？如果实例本身就有相应的response,那么就会响应之，如果没有系统就会发出methodSignatureForSelector消息，寻问它这个消息是否有效？有效就返回对应的方法地址之类的，无效则返回nil。消息转发机制使用从这个方法中获取的信息来创建NSInvocation对象。因此我们必须重写这个方法，为给定的selector提供一个合适的方法签名。
// Here, we ask the two real objects, realObject1 first, for their metho
// 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 = [self.realObject1 methodSignatureForSelector:aSelector];
    if (sig){
        return sig;
    }
    sig = [self.realObject2 methodSignatureForSelector:aSelector];
    if (sig){
        return sig;
    }
    return nil;
}

// Invoke the invocation on whichever real object had a signature for it.
- (void)forwardInvocation:(NSInvocation *)invocation {
    id target = [self.realObject1 methodSignatureForSelector:[invocation selector]] ? self.realObject1 : self.realObject2;
    [invocation invokeWithTarget:target];

　　//或者用下列方法
　　/*
    　　id target;
    　　if([self.realObject1 respondsToSelector:[invocation selector]]) {
        　　target = self.realObject1;
    　　} else if([self.realObject2 respondsToSelector:[invocation selector]]) {
       　　 target = self.realObject2;
   　　 }
    　　[invocation invokeWithTarget:target];
　　*/
}

NSMutableString *string = [NSMutableString new];
NSMutableArray *array = [NSMutableArray new];
id proxy = [[SLVForwardInvocation 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!"];
                
if ([[proxy objectAtIndex:0] isEqualToString:@"This is a test!"]) {
     NSLog(@"Appending successful.");  
 } else {  
     NSLog(@"Appending failed, got: ‘%@‘", proxy);  
}

////  NSObject+Forwarding.m
#import "SLVStubProxy.h"
#import <objc/runtime.h>

@implementation NSObject (Forwarding)
+ (void)load{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class class = [self class];
        
        SEL originalSelector = @selector(forwardingTargetForSelector:);
        SEL swizzledSelector = @selector(newForwardingTargetForSelector:);
        // 通过class_getInstanceMethod()函数从当前对象中的method list获取method结构体，如果是类方法就使用class_getClassMethod()函数获取。
        Method originalMethod = class_getInstanceMethod(class, originalSelector);
        Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
        /**
         *  我们在这里使用class_addMethod()函数对Method Swizzling做了一层验证，如果self没有实现被交换的方法，会导致失败。
         *  而且self没有交换的方法实现，但是父类有这个方法，这样就会调用父类的方法，结果就不是我们想要的结果了。
         *  所以我们在这里通过class_addMethod()的验证，如果self实现了这个方法，class_addMethod()函数将会返回NO，我们就可以对其进行交换了。
         */
        
        BOOL didAddMethod = class_addMethod(class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
        if (didAddMethod) {
            class_replaceMethod(class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
        }else{
            method_exchangeImplementations(originalMethod, swizzledMethod);
        }
    });
}

-(id) newForwardingTargetForSelector:(SEL)aSelector {
    SLVStubProxy *proxy = [SLVStubProxy new];
    return proxy;
}


// SLVStubProxy.m
#import "SLVStubProxy.h"
#import <objc/runtime.h>

@implementation SLVStubProxy
+ (BOOL) resolveInstanceMethod:(SEL)selector {
    
    // 向类中动态的添加方法，第三个参数为函数指针，指向待添加的方法。最后一个参数表示待添加方法的“类型编码”
    class_addMethod(self, selector,(IMP)autoAddMethod,"v@:@");
   
    return YES;
}

id autoAddMethod(id self, SEL _cmd) {
    return 0;
}
@end