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Runtime之常见崩溃问题

Runtime之常见崩溃问题

作者: 嗯o哼 | 来源:发表于2020-09-17 20:40 被阅读0次

    一、iOS常见的崩溃类型

    • unrecognized selector sent to instance 调用了不存在的方法
    • NSArray、NSMutableArray 数组越界、插入空值等
    • NSDictionary、NSMutableDictionary 初始化有nil值、key为nil等

    二、崩溃类型及解决方案

    unrecognized selector sent to instance
    产生的原因
    找不到该对象的方法,系统发出异常

    解决方案

    对象调用方法经过三个阶段
    1.消息发送:查询cache和方法列表,找到了直接调用,找不到方法会进入下个阶段
    2.动态解析: 调用resolveInstanceMethod或resolveClassMethod方法里面可以有一次动态添加方法的机会
    3.消息转发:1.首先会判断是否有其他对象可以处理方法forwardingTargetForSelector返回一个新的对象2.如果没有新的对象进行处理,会调用methodSignatureForSelector方法返回方法签名,然后调用forwardInvocation

    #import "NSObject+Extension.h"
    #import <objc/runtime.h>
    
    @implementation NSObject (Extension)
    
    +(void)load{
        
        Method method1 = class_getInstanceMethod([self class], @selector(methodSignatureForSelector:));
        Method method2 = class_getInstanceMethod(self, @selector(pf_methodSignatureForSelector:));
        method_exchangeImplementations(method1, method2);
        
        Method method3 = class_getInstanceMethod([self class], @selector(forwardInvocation:));
        Method method4 = class_getInstanceMethod(self, @selector(pf_forwardInvocation:));
        method_exchangeImplementations(method3, method4);
        
    }
    
    // 返回处理对象
    //-(id)forwardingTargetForSelector:(SEL)aSelector{}
    
    -(NSMethodSignature *)pf_methodSignatureForSelector:(SEL)aSelector{
        
        // 获取方法签名
    //    NSMethodSignature *signature = [self pf_methodSignatureForSelector:aSelector];
        
        NSMethodSignature *signature = [NSObject instanceMethodSignatureForSelector:@selector(proxyMethod)];
        return signature;
    }
    
    -(void)pf_forwardInvocation:(NSInvocation *)anInvocation{
        
        //可以做些别的什么事情
       
    }
    
    -(void)proxyMethod{
        
    }
    
    @end
    
    

    NSArray、NSMutableArray 数组越界、插入空值等

    NSArray相关

       NSArray *array = @[@"12",@"31"];
        // 1.1 读取下标越界
        // 通过下标访问元素,会调用objectAtIndexedSubscript方法
        NSString *value = array[3];//数组越界,导致崩溃
        // 1.2通过方法objectAtIndex访问元素
        [array objectAtIndex:3]; // 数组越界、导致崩溃
    

    解决方法

    注意NSArray 是一个类簇,它真正的类型是__NSArrayI
    为NSArray写一个分类,利用runtime 替换系统的objectAtIndexedSubscript方法,判断是否越界

    +(void)load{
        
        Class cls = NSClassFromString(@"__NSArrayI");
        Method method1 = class_getInstanceMethod(cls, @selector(objectAtIndexedSubscript:));
        Method method2 = class_getInstanceMethod(self, @selector(pf_objectAtIndexedSubscript:));
        method_exchangeImplementations(method1, method2);
    
        Method method3 = class_getInstanceMethod(cls, @selector(objectAtIndex:));
        Method method4 = class_getInstanceMethod(self, @selector(pf_objectAtIndex:));
        method_exchangeImplementations(method3, method4);
    }
    
    -(id)pf_objectAtIndexedSubscript:(NSUInteger)idx{
        if (idx > self.count - 1) {
            NSAssert(NO, @"数组越界了");
            return nil;
        }else{
            return [self pf_objectAtIndexedSubscript:idx];
        }
    }
    
    -(id)pf_objectAtIndex:(NSUInteger)index{
        if (index > self.count - 1) {
            NSAssert(NO, @"数组越界了");
            return nil;
        }else{
            return [self pf_objectAtIndex:index];
        }
    }
    

    NSMutableArray相关

    注意NSMutableArray 真正的类型是__NSArrayM

       NSArray *array = @[@"12",@"31"];
        // 1.1 读取下标越界
        // 通过下标访问元素,会调用objectAtIndexedSubscript方法
        NSString *value = array[3];//数组越界,导致崩溃
        // 1.2通过方法objectAtIndex访问元素
        [array objectAtIndex:3]; // 数组越界、导致崩溃
        
        NSMutableArray *mArray = [NSMutableArray arrayWithArray:array];
        // 2.1 读取下标越界
        NSString *str = mArray[3];// 数组越界、导致崩溃
        // 2.2 通过下标进行赋值
        NSString *s;
        mArray[4] = s; // 1.数组越界 2.空值导致崩溃
        // 2.3 插入数据 会调用insertObject:atIndex:
        [mArray addObject:nil]; // 插入nil值导致崩溃
        // 2.4 移除元素越界 会调用removeObjectsInRange方法
        [mArray removeObjectAtIndex:4];
    

    解决方案

    #import "NSMutableArray+Extension.h"
    #import <objc/runtime.h>
    
    @implementation NSMutableArray (Extension)
    
    +(void)load{
        
        Class cls = NSClassFromString(@"__NSArrayM");
        // mArray[4] 会调用方法objectAtIndexedSubscript 取值
        Method method1 = class_getInstanceMethod(cls, @selector(objectAtIndexedSubscript:));
        Method method2 = class_getInstanceMethod(self, @selector(pf_objectAtIndexedSubscript:));
        method_exchangeImplementations(method1, method2);
        
        // mArray[4] 会调用setObject:atIndexedSubscript: 赋值
        Method method3 = class_getInstanceMethod(cls, @selector(setObject:atIndexedSubscript:));
        Method method4 = class_getInstanceMethod(self, @selector(pf_setObject:atIndexedSubscript:));
        method_exchangeImplementations(method3, method4);
        
    //    [marray addobject] 会调用insertObject atIndex
        Method method5 = class_getInstanceMethod(cls, @selector(insertObject:atIndex:));
        Method method6 = class_getInstanceMethod(self, @selector(pf_insertObject:atIndex:));
        method_exchangeImplementations(method5, method6);
        
        Method method7 = class_getInstanceMethod(cls, @selector(removeObjectAtIndex:));
        Method method8 = class_getInstanceMethod(self, @selector(pf_removeObjectAtIndex:));
        method_exchangeImplementations(method7, method8);
        
    }
    
    // 防止数组越界导致崩溃
    -(id)pf_objectAtIndexedSubscript:(NSUInteger)idx{
        if (idx > self.count - 1) {
    //        NSAssert(NO, @"index %zd 越界",idx);
            return nil;
        }
        return [self pf_objectAtIndexedSubscript:idx];
    }
    
    -(void)pf_setObject:(id)obj atIndexedSubscript:(NSUInteger)idx{
        // 不能越界
        if (idx > self.count - 1) {
    //        NSAssert(NO, @"index %zd 越界",idx);
            return;
        }
        // 不能插入空值
        if (obj == nil) {
    //        NSAssert(NO, @"不能插入nil值");
            return;
        }
        
        [self pf_setObject:obj atIndexedSubscript:idx];
    }
    
    
    -(void)pf_insertObject:(id)anObject atIndex:(NSUInteger)index{
        if (!anObject) {
    //        NSAssert(NO, @"不能插入nil值");
            return;
        }
        [self pf_insertObject:anObject atIndex:index];
        
    }
    
    -(void)pf_removeObjectAtIndex:(NSUInteger)index{
        if (index > self.count - 1) {
            return;
        }
        [self pf_removeObjectAtIndex:index];
    }
    @end
    
    

    NSDictionary 相关

    NSDictionary 也是一个类簇,它有多种类型

    有时候,我们创建一个NSDictionary对象的时候,会直接使用@{}方法创建,而当有一个value为nil 的时候,也会导致崩溃的现象

    NSString *str;
    // 这种创建方式会调用__NSPlaceholderDictionary 的initWithObjects:forKeys:count:方法
        NSDictionary *dict = @{
            @"a":@"A",
            @"b":str
        };
    // 如果key为nil 获取值也会导致崩溃,调用的是__NSDictionaryI的objectForKeyedSubscript方法
    NSString *value = dict[str]
    

    解决方案 替换此方法

    //__NSPlaceholderDictionary
        Class cls = NSClassFromString(@"__NSPlaceholderDictionary");
        Method method1 = class_getInstanceMethod(cls, @selector(initWithObjects:forKeys:count:));
        Method method2 = class_getInstanceMethod(self, @selector(pf_initWithObjects:forKeys:count:));
        method_exchangeImplementations(method1, method2);
    
    //__NSDictionaryI
        Class cls2 = NSClassFromString(@"__NSDictionaryI");
        Method method3 = class_getInstanceMethod(cls2, @selector(objectForKeyedSubscript:));
        Method method4 = class_getInstanceMethod(self, @selector(pf_objectForKeyedSubscript:));
        method_exchangeImplementations(method3, method4);
    
    // 初始化的时候,空值导致崩溃
    -(instancetype)pf_initWithObjects:(id  _Nonnull const [])objects forKeys:(id<NSCopying>  _Nonnull const [])keys count:(NSUInteger)cnt{
        
        // 注意 objects 和keys 都是c语言的,所以要创建c语言的数组
        NSUInteger index = 0;// 数组下标,用于数据存入正确的位置
        id objectsArray[cnt]; // values
        id<NSCopying> keysArray[cnt];//keys
        
        for (int i = 0; i < cnt; i++) {
            // 如果值和key 都不为nil
            if (objects[i] != nil && keys[i] != nil) {
                objectsArray[index] = objects[i];
                keysArray[index] = keys[i];
                index++;
            }else{
                NSString *str = [NSString stringWithFormat:@"%@不能为空",keys[i]];
                NSAssert(NO, str);
            }
        }
        
        return [self pf_initWithObjects:objectsArray forKeys:keysArray count:index];
    }
    
    -(id)pf_objectForKeyedSubscript:(id)key{
        if (!key) {
            NSAssert(NO, @"key 不能为空");
            return nil;
        }
        
        id obj = [self pf_objectForKeyedSubscript:key];
        
        if ([obj isKindOfClass:[NSNull class]]) {
            return nil;
        }
        
        return [self pf_objectForKeyedSubscript:key];
    }
    

    NSMutableDictionary相关

    NSMutableDictionary 一般是__NSDictionaryM

     /// 通过类名字符串创建类
        Class cls = NSClassFromString(@"__NSDictionaryM");
        Method method1 = class_getInstanceMethod(cls, @selector(setObject:forKeyedSubscript:));
        Method method2 = class_getInstanceMethod(self, @selector(pf_setObject:forKeyedSubscript:));
        
        method_exchangeImplementations(method1, method2);
        
        Method method3 = class_getInstanceMethod(cls, @selector(setValue:forKey:));
        Method method4 = class_getInstanceMethod(self, @selector(pf_setObject:forKey:));
        method_exchangeImplementations(method3, method4);
        
        Method method5 = class_getInstanceMethod(cls, @selector(objectForKeyedSubscript:));
        Method method6 = class_getInstanceMethod(self, @selector(pf_objectForKeyedSubscript:));
        method_exchangeImplementations(method5, method6);
    
    -(void)pf_setObject:(id)obj forKeyedSubscript:(id<NSCopying>)key{
        if (!key) return;// 如果key为nil 会导致崩溃
        [self pf_setObject:obj forKeyedSubscript:key];
    }
    
    //拦截系统的setObject forKey方法
    -(void)pf_setObject:(id)anObject forKey:(id<NSCopying>)aKey{
        // 1.当key为nil 的时候,set方法会崩溃
        if (!aKey) return;
        [self pf_setObject:anObject forKey:aKey];
    }
    
    -(id)pf_objectForKeyedSubscript:(id)key{
        if (!key) {
            return nil;
        }
        
        id obj = [self pf_objectForKeyedSubscript:key];
        
        if ([obj isKindOfClass:[NSNull class]]) {
            return nil;
        }
        
        return [self pf_objectForKeyedSubscript:key];
    }
    

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