标签：sources created int 调用 objc cti invalid 5.7 type
最近在看消息转发的资料，发现大部分都是理论知识，很少有完整的代码。现在以代码的形式形象的解释一下：
用Xcode创建一个工程
创建一个类Person 代码如下
Person.h代码如下：
#import <Foundation/Foundation.h> @interface Person : NSObject - (instancetype)init NS_UNAVAILABLE; - (instancetype)initWithUserName:(NSString *)userName; - (void)logUserName; @end
Person.m代码如下：
#import "Person.h" @interface Person() @property (nonatomic, copy) NSString *userName; @end @implementation Person - (instancetype)initWithUserName:(NSString *)userName { self = [super init]; if (self) { _userName = [userName copy]; } return self; } - (void)logUserName { NSLog(@"userName = %@", self.userName); } @end
ViewController.m代码如下：
#import "ViewController.h" #import "Person.h" @interface ViewController () @end @implementation ViewController - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib. Person *person = [[Person alloc] initWithUserName:@"小王"]; [person logUserName]; } - (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; // Dispose of any resources that can be recreated. } @end
运行工程结果为：
2017-03-01 22:47:07.296 RunTimeDemo[24364:1776826] userName = 小王
结果正常
把Person.m 的logUserName方法删除，此时Person.m 的代码如下：
#import "Person.h" @interface Person() @property (nonatomic, copy) NSString *userName; @end @implementation Person - (instancetype)initWithUserName:(NSString *)userName { self = [super init]; if (self) { _userName = [userName copy]; } return self; } @end
运行工程会出现 如下结果
2017-03-01 23:06:25.788 RunTimeDemo[24729:1788071] -[Person logUserName]: unrecognized selector sent to instance 0x608000018e00 2017-03-01 23:06:25.796 RunTimeDemo[24729:1788071] *** Terminating app due to uncaught exception ‘NSInvalidArgumentException‘, reason: ‘-[Person logUserName]: unrecognized selector sent to instance 0x608000018e00‘
假如不在Person类中实现logUsrName这个方法，也可以让工程正常运行，此时就涉及到消息转发，Objective-C运行时会给出三次拯救程序崩溃的机会。
如下：
objc运行时会调用+resolveInstanceMethod:或者 +resolveClassMethod:，让你有机会提供一个函数实现。如果你添加了函数，那运行时系统就会重新启动一次消息发送的过程，否则 ，运行时就会移到下一步，消息转发（Message Forwarding）。
如果目标对象实现了-forwardingTargetForSelector:，Runtime 这时就会调用这个方法，给你把这个消息转发给其他对象的机会。 只要这个方法返回的不是nil和self，整个消息发送的过程就会被重启，当然发送的对象会变成你返回的那个对象。否则，就会继续Normal Fowarding。 这里叫Fast，只是为了区别下一步的转发机制。因为这一步不会创建任何新的对象，但下一步转发会创建一个NSInvocation对象，所以相对更快点。
这一步是Runtime最后一次给你挽救的机会。首先它会发送-methodSignatureForSelector:消息获得函数的参数和返回值类型。如果-methodSignatureForSelector:返回nil，Runtime则会发出-doesNotRecognizeSelector:消息，程序这时也就挂掉了。如果返回了一个函数签名，Runtime就会创建一个NSInvocation对象并发送-forwardInvocation:消息给目标对象。
下面就验证一下上面所对应的函数的执行顺序：
Person.m的代码如下：
#import "Person.h" #define LOG_FunctionName NSLog(@"%s", __func__) @interface Person() @property (nonatomic, copy) NSString *userName; @end @implementation Person- (instancetype)initWithUserName:(NSString *)userName { self = [super init]; if (self) { _userName = [userName copy]; } return self; } + (BOOL)resolveInstanceMethod:(SEL)sel { LOG_FunctionName; return YES; } - (id)forwardingTargetForSelector:(SEL)aSelector { LOG_FunctionName; return [super forwardingTargetForSelector:aSelector]; } - (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector { LOG_FunctionName; return [super methodSignatureForSelector:aSelector]; } - (void)forwardInvocation:(NSInvocation *)anInvocation { LOG_FunctionName; } @end
运行结果为：
2017-03-01 23:45:21.723 RunTimeDemo[25672:1817388] +[Person resolveInstanceMethod:] 2017-03-01 23:45:21.724 RunTimeDemo[25672:1817388] -[Person forwardingTargetForSelector:] 2017-03-01 23:45:21.724 RunTimeDemo[25672:1817388] -[Person methodSignatureForSelector:] 2017-03-01 23:45:21.724 RunTimeDemo[25672:1817388] +[Person resolveInstanceMethod:] 2017-03-01 23:45:21.725 RunTimeDemo[25672:1817388] -[Person logUserName]: unrecognized selector sent to instance 0x60000001cef0 2017-03-01 23:45:21.729 RunTimeDemo[25672:1817388] *** Terminating app due to uncaught exception ‘NSInvalidArgumentException‘, reason: ‘-[Person logUserName]: unrecognized selector sent to instance 0x60000001cef0‘
运行结果正好验证了上述说明。
标签：sources created int 调用 objc cti invalid 5.7 type
原文地址：http://www.cnblogs.com/lidaojian/p/6487110.html
