用法一: Unrecognized Selector类型crash防护（Unrecognized Selector）
先介绍下class_addMethod这个方法:
/**
Class _Nullable cls: 你要添加方法的那个类；
SEL _Nonnull name：name都说可以随便取, 但有些场景随便取会有问题（如下例：），一些取添加或替换方法的名称SEL；
IMP _Nonnull imp：新方法的 IMP；
const char * _Nullable types：新方法的返回值及参数
*/
class_addMethod(Class _Nullable cls, SEL _Nonnull name, IMP _Nonnull imp, const char * _Nullable types)
开发中经常会遇到这个问题------“unrecognized selector sent to instance 0x7faa2a132c0” 而导致cash. 为了防止crash我们可以用class_addMethod给找不到对应方法即将crash的消息添加一个与之对应的方法来防止其因为找不到相应方法而crash.
在OC中找不到对相应的实现方法时, 有补救机制 即 会先调用动态决议方法 该方法解决不了问题 再调用重定向方法; 若都解决不了再 cash.
动态决议方法：(这是给类利用class_addMethod添加函数的机会...)
- (BOOL)resolveClassMethod:(SEL)sel OBJC_AVAILABLE(10.5, 2.0, 9.0, 1.0);
- (BOOL)resolveInstanceMethod:(SEL)sel OBJC_AVAILABLE(10.5, 2.0, 9.0, 1.0);
重定向方法：
- (id)forwardingTargetForSelector:(SEL)aSelector OBJC_AVAILABLE(10.5, 2.0, 9.0, 1.0);
- (void)forwardInvocation:(NSInvocation *)anInvocation;
补救机制(拦截调用)的整个流程即Objective——C的消息转发机制。其具体流程如下图：
image.png
下面上代码: 给一个类的对象调用一个未实现的方法 然后用runtime 在动态决议方法中为其添加实现, 防止crash
/* Person 类 */
#import "Person.h"
#import <objc/runtime.h>
@implementation Person
+ (BOOL)resolveInstanceMethod:(SEL)sel {
NSLog(@"resolveInstanceMethod: %@", NSStringFromSelector(sel)); // 打印： eat
Method addMethod = class_getInstanceMethod([self class], @selector(addMethod));
// 这里 SEL _Nonnull name 必须写 sel, 否则还是会cash...
class_addMethod([self class], sel, method_getImplementation(addMethod), method_getTypeEncoding(addMethod));
return true;
}
/*
* 这个方法也可以解决cash问题, 意思是转给新的对象去执行这个方法...
- (id)forwardingTargetForSelector:(SEL)aSelector {
NSLog(@"forwardingTargetForSelector: %@",NSStringFromSelector(aSelector));
if (aSelector == @selector(eat)) {
// 创建新的对象
StubProxyObject * stub = [[StubProxyObject alloc] init];
return stub;
}
return [super forwardingTargetForSelector:@selector(addMethod)];
}
*/
- (void) addMethod {
NSLog(@"addMethod");
}
@end
// 调用 Person未实现方法eat
Person * person = [[Person alloc] init];
[person performSelector:@selector(eat)];
添加后就不会cash;
用法二: 替换系统的方法:
代码示例: 创建 UIViewController 分类, 然后替换 - (void)dismissViewControllerAnimated: (BOOL)flag completion: (void (^ __nullable)(void))completion;
#import "UIViewController+Extention.h"
#import <objc/runtime.h>
@implementation UIViewController (Extention)
+ (void)load {
Class class = [self class];
// 保证方法替换只执行一次
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
SEL originSelector = @selector(dismissViewControllerAnimated:completion:);
SEL swizzledSelector = @selector(customDismissViewController);
Method oringinMethod = class_getInstanceMethod(class, originSelector);
Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
IMP swizzledIMP = method_getImplementation(swizzledMethod);
const char * type = method_getTypeEncoding(swizzledMethod);
BOOL didAddMethod = class_addMethod(class, originSelector, swizzledIMP, type);
if (didAddMethod) {
class_replaceMethod(class, swizzledSelector, method_getImplementation(oringinMethod), method_getTypeEncoding(oringinMethod));
} else {
method_exchangeImplementations(oringinMethod, swizzledMethod);
}
});
}
- (void) customDismissViewController {
NSLog(@"customDismissViewController");
// 这里调用不会有 死循环....
[self customDismissViewController];
}
还可以写为:
+ (void)load {
Class class = [self class];
SEL originSelector = @selector(dismissViewControllerAnimated:completion:);
SEL swizzledSelector = @selector(customDismissViewController);
Method originMethod = class_getInstanceMethod(class, originSelector);
Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
// 确保两个方法都得获取到
if (!originMethod || !swizzledMethod) {
return;
}
// 交换跟上面情况一样
// method_exchangeImplementations(originMethod, swizzledMethod);
// 这种只是作替换，既自定义方法里 不能再调用 [self customDismissViewController];
class_replaceMethod(class, originSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
// class_replaceMethod(class, swizzledSelector, method_getImplementation(originMethod), method_getTypeEncoding(originMethod));
}
- (void) customDismissViewController {
NSLog(@"customDismissViewController");
// 这里不能调, 不然会产生死循环...
// [self customDismissViewController];
}
应用场景: 如何通过不去手动修改每个UIImage的imageNamed：方法就可以实现为该方法中加入版本判断语句？ 可以为 UIImage建一个分类（UIImage+Category）, 替换系统的 imageNamed: 方法; 注意: 替换方法后,最后要调用一下自己定义替换的方法, 让其有加载图片的功能...
用法三: 在不同类之间实现Method Swizzling
示例: Person类有一个实例方法 - (void)run:(CGFloat)speed, 目前需要Hook该方法对速度大于20才执行 run, 利用另一个类的方法交换来实现:
Person类
#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>
@interface Person : NSObject
- (void) run: (CGFloat)speed;
@end
#import "Person.h"
#import <objc/runtime.h>
@implementation Person
- (void) run: (CGFloat)speed {
NSLog(@"person --- %f",speed);
}
@end
StubProxyObject 类
#import "StubProxyObject.h"
#import <UIKit/UIKit.h>
#import <objc/runtime.h>
@implementation StubProxyObject
+(void)load {
Class originClass = NSClassFromString(@"Person");
Class swizzledClass = [self class];
SEL originSelector = NSSelectorFromString(@"run:");
SEL swizzledSelector = @selector(stub_run:);
Method originMethod = class_getInstanceMethod(originClass, originSelector);
Method swizzledMethod = class_getInstanceMethod(swizzledClass, swizzledSelector);
// 向Person类中新添加 stub_run: 方法
BOOL addMethod = class_addMethod(originClass, swizzledSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
if (!addMethod) {
return;
}
// 获取当前 Person 中新添加的方法 stub_run:的Method指针
Method newSwizzledMethod = class_getInstanceMethod(originClass, swizzledSelector);
if (!newSwizzledMethod) {
return;
}
BOOL didAddMethod = class_addMethod(originClass, originSelector, method_getImplementation(newSwizzledMethod), method_getTypeEncoding(newSwizzledMethod));
if (didAddMethod) {
class_replaceMethod(originClass, swizzledSelector , method_getImplementation(originMethod), method_getTypeEncoding(originMethod));
} else {
method_exchangeImplementations(originMethod, newSwizzledMethod);
}
}
- (void) stub_run: (CGFloat) merter {
NSLog(@"StubProxyObject --- stub_run");
if (merter > 20) {
[self stub_run:merter];
}
}
@end
然后在其它地方 Person 对象调用 run: 方法时:
Person * person = [Person new];
[person run:30];
控制台会打印:
StubProxyObject --- stub_run
person --- 30.000000
用法四: 给分类添加属性:
我们知道, 分类中是无法设置属性的，如果在分类的声明中写@property, 能为其生成get 和 set 方法的声明，但无法生成成员变量，就是说虽然点语法能调用出来，但程序执行后会crash...
示例: 给NSObject添加分类(NSObject+Category)设置属性
#import <Foundation/Foundation.h>
@interface NSObject (Extention)
@property (nonatomic, strong) NSString * name;
@end
#import "NSObject+Extention.h"
#import <objc/runtime.h>
static char * const nameKey = "nameKey";
@implementation NSObject (Extention)
- (void)setName:(NSString *)name {
objc_setAssociatedObject(self, nameKey, name, OBJC_ASSOCIATION_COPY_NONATOMIC);
}
- (NSString *)name {
return objc_getAssociatedObject(self, nameKey);
}
@end
用法五: 利用runtime进行解归档操作
首先得知道三个方法:
- 获得某个类的所有成员变量（outCount 会返回成员变量的总数）
Ivar *class_copyIvarList(Class cls , unsigned int *outCount)
- 获得成员变量的名字
const char *ivar_getName(Ivar v)
- 获得成员变量的类型
const char *ivar_getTypeEndcoding(Ivar v)
利用runtime 获取所有属性来重写归档解档方法(对于类中属性比较多时, 用runtime来解归档比较方便)
// 设置不需要归解档的属性
- (NSArray *)ignoredNames {
return @[@"_aaa",@"_bbb",@"_ccc"];
}
// 归档调用方法
- (void)encodeWithCoder:(NSCoder *)aCoder {
// 获取所有成员变量
unsigned int outCount = 0;
Ivar *ivars = class_copyIvarList([self class], &outCount);
for (int i = 0; i < outCount; i++) {
Ivar ivar = ivars[i];
// 获得成员变量的名字
const char * name = ivar_getName(ivar);
// 将每个成员变量名转换为NSString对象类型
NSString *key = [NSString stringWithUTF8String:name];
// 忽略不需要归档的属性
if ([[self ignoredNames] containsObject:key]) {
continue;
}
// 通过成员变量名，取出成员变量的值
id value = [self valueForKeyPath:key];
// 再将值归档
[aCoder encodeObject:value forKey:key];
// 这两步就相当于 [aCoder encodeObject:@(self.age) forKey:@"_age"];
}
free(ivars);
}
// 解档方法
- (instancetype)initWithCoder:(NSCoder *)aDecoder {
if (self = [super initWithCoder:aDecoder]) {
// 获取所有成员变量
unsigned int outCount = 0;
Ivar *ivars = class_copyIvarList([self class], &outCount);
for (int i = 0; i < outCount; i++) {
Ivar ivar = ivars[i];
// 获得成员变量的名字
const char * name = ivar_getName(ivar);
// 将每个成员变量名转换为NSString对象类型
NSString *key = [NSString stringWithUTF8String:name];
// 忽略不需要解档的属性
if ([[self ignoredNames] containsObject:key]) {
continue;
}
// 根据变量名解档取值，无论是什么类型
id value = [aDecoder decodeObjectForKey:key];
// 取出的值再设置给属性
[self setValue:value forKey:key];
// 这两步就相当于以前的 self.age = [aDecoder decodeObjectForKey:@"_age"];
}
free(ivars);
}
return self;
}
若项目中解归档的类比较多时, 就可以考虑 NSObject 分类来写上述逻辑了....
NSObject+Extension.h
#import <Foundation/Foundation.h>
@interface NSObject (Extention)
@property (nonatomic, strong) NSString * name;
- (NSArray *)ignoredNames;
- (void)encode:(NSCoder *)aCoder;
- (void)decode:(NSCoder *)aDecoder;
@end
NSObject+Extention.m
#import "NSObject+Extension.h"
#import <objc/runtime.h>
@implementation NSObject (Extension)
// 归档调用方法
- (void)encode:(NSCoder *)aCoder {
// 一层层父类往上查找，对父类的属性执行归解档方法
Class c = self.class;
while (c &&c != [NSObject class]) {
unsigned int outCount = 0;
Ivar *ivars = class_copyIvarList([self class], &outCount);
for (int i = 0; i < outCount; i++) {
Ivar ivar = ivars[i];
NSString *key = [NSString stringWithUTF8String:ivar_getName(ivar)];
// 如果有实现该方法再去调用
if ([self respondsToSelector:@selector(ignoredNames)]) {
if ([[self ignoredNames] containsObject:key]) continue;
}
id value = [self valueForKeyPath:key];
[aCoder encodeObject:value forKey:key];
}
free(ivars);
c = [c superclass];
}
}
// 解档方法
- (void)decode:(NSCoder *)aDecoder {
// 一层层父类往上查找，对父类的属性执行归解档方法
Class c = [self class];
while (c &&c != [NSObject class]) {
unsigned int outCount = 0;
Ivar *ivars = class_copyIvarList(c, &outCount);
for (int i = 0; i < outCount; i++) {
Ivar ivar = ivars[i];
NSString *key = [NSString stringWithUTF8String:ivar_getName(ivar)];
// 如果有实现该方法再去调用
if ([self respondsToSelector:@selector(ignoredNames)]) {
if ([[self ignoredNames] containsObject:key]) continue;
}
id value = [aDecoder decodeObjectForKey:key];
[self setValue:value forKey:key];
}
free(ivars);
c = [c superclass];
}
}
@end
在需要归解档的对象中实现下面方法即可：
// 设置需要忽略的属性
- (NSArray *)ignoredNames {
return @[@"_aaa"];
}
// 在系统方法内来调用我们的方法
- (instancetype)initWithCoder:(NSCoder *)aDecoder {
if (self = [super init]) {
[self decode:aDecoder];
}
return self;
}
- (void)encodeWithCoder:(NSCoder *)aCoder {
[self encode:aCoder];
}
然而多个类需要解归档时, 上面的代码还是重复的, 所以我们直接可以定义个宏, 在需要的类里直接一句宏就搞定了,这也是MJExtention里一句宏搞定解归档的实现原理;
在 NSObject+Extension.h 里, 我们定义一个宏:
#define YQCodingImplementation \
-(void)encodeWithCoder:(NSCoder *)aCoder\
{\
[self encode:aCoder];\
}\
-(instancetype)initWithCoder:(NSCoder *)aDecoder\
{\
if (self = [super init]) {\
[self decode:aDecoder];\
}return self; \
}
然后在需要的类里:
#import "Person.h"
#import "NSObject+HZCoding.h"
@implementation Person
// 归档 解档 , 一句宏就可以了...
YQCodingImplementation
@end
用法六: 利用runtime 获取所有属性来进行字典转模型
可以看参考文章, 里面写的比较详细了....
参考文章: https://www.jianshu.com/p/ab966e8a82e2
http://www.cocoachina.com/ios/20161102/17920.html
