1. 數(shù)組越界 訪問為空是我們的app的一大元兇,當(dāng)訪問數(shù)組經(jīng)常會(huì)訪問為空,這是就會(huì)拋出異常導(dǎo)致app閃退,有時(shí)當(dāng)我們測試時(shí)數(shù)據(jù)是好的,但是在上線以后有可能后臺(tái)修改數(shù)據(jù)有問題,導(dǎo)致前段訪問數(shù)據(jù)時(shí)造成訪問數(shù)組訪問為空越界,

2. 可變數(shù)組添加元素是,元素不能為空,當(dāng)為空時(shí)將發(fā)出異常,導(dǎo)致app崩潰閃退

下面我將介紹使用runtime替換系統(tǒng)的方法防止數(shù)組增刪改查出現(xiàn)問題直接崩潰

首先創(chuàng)建一個(gè)類目 繼承自NSMutableArray

@interface NSMutableArray (categary)

導(dǎo)入#import <objc/runtime.h>

使用系統(tǒng)的類方法+load{}

這里先介紹load方法+load方法是一個(gè)類方法,應(yīng)用啟動(dòng)的時(shí)候加載所有的類,這時(shí)就會(huì)調(diào)用類方法

load方法被添加到runtime時(shí)開始執(zhí)行 父類首先執(zhí)行,之后是子類最后才到categary 又因?yàn)槭侵苯荧@取函數(shù)指針來執(zhí)行，不會(huì)像 objc_msgSend 一樣會(huì)有方法查找的過程

+ (void)load
    {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
   
        Method newMethod = class_getClassMethod([self class], @selector(cq_objectAtIndex:));
        Method method = class_getClassMethod([self class], @selector(objectAtIndex:));
    
        //交換系統(tǒng)的取數(shù)組元素的方法
       method_exchangeImplementations(newMethod, method);
        
        
        Method addNewMethod = class_getClassMethod([self class], @selector(cq_addObject:));
        Method addmethod = class_getClassMethod([self class], @selector(addObject:));

       //交換系統(tǒng)添加元素到數(shù)組的方法        
    method_exchangeImplementations(addNewMethod, addmethod);
        
        
        Method removeNewMethod = class_getClassMethod([self class], @selector(cq_safeRemoveObject:));
        Method removemethod = class_getClassMethod([self class], @selector(removeObject:));

    //交換系統(tǒng)移除數(shù)組元素的方法      
  method_exchangeImplementations(removeNewMethod, removemethod);
        
    });
    }

這里使用GCD的單例表示是只創(chuàng)建一次,因?yàn)槊看晤愓{(diào)用的時(shí)候都會(huì)加載load類方法

 //取值
- (id)cq_objectAtIndex:(NSUInteger)index
{
    if (self.count == 0) {
        NSLog(@"%s mutArray None Object",__func__);
        return nil;
    }
    
   if (index > self.count) {
        NSLog(@"%s index out of mutArrayCount",__func__);
        
        return nil;
    }
    
    return [self cq_objectAtIndex:index];
    
}

//向數(shù)組添加元素
- (void)cq_addObject:(id)object
{`
    if (object == nil) {
        NSLog(@"%s can add nil object into NSMutableArray", __FUNCTION__);
    } else {
        [self cq_addObject:object];
    }
}

//移除指定下標(biāo)元素
- (void)cq_RemoveObjectAtIndex:(NSUInteger)index {
    if (self.count <= 0) {
        NSLog(@"%s can't get any object from an empty array", __FUNCTION__);
        return;
    }
    
    if (index >= self.count) {
        NSLog(@"%s index out of bound", __FUNCTION__);
        return;
    }
    
    [self cq_RemoveObjectAtIndex:index];
}

//插入元素到指定下標(biāo)位置
- (void)cq_insertObject:(id)anObject atIndex:(NSUInteger)index {
    if (anObject == nil) {
        NSLog(@"%s can't insert nil into NSMutableArray", __FUNCTION__);
    } else if (index > self.count) {
        NSLog(@"%s index is invalid", __FUNCTION__);
    } else {
        [self cq_insertObject:anObject atIndex:index];
    }
}

//移除特定元素
- (void)cq_safeRemoveObject:(id)obj {
    if (obj == nil) {
        NSLog(@"%s call -removeObject:, but argument obj is nil", __FUNCTION__);
        return;
    }
    
    [self cq_safeRemoveObject:obj];
}