第17月第7天 iOS 数组越界，防Crash处理

上面方法已经可以避免crash，为了避免冗余的代码，写一个NSArray的分类，利用runtime替换NSArray的对象方法objectAtIndex：，在这里进行判断，捕获异常：


#import <Foundation/Foundation.h>

@interface NSArray (Crash)

@end

/*** ---------------分割线--------------- ***/ 

#import "NSArray+Crash.h"
#import <objc/runtime.h>

@implementation NSArray (Crash)

+ (void)load
{
    [super load];
    
    //替换不可变数组方法
    Method oldObjectAtIndex = class_getInstanceMethod(objc_getClass("__NSArrayI"), @selector(objectAtIndex:));
    Method newObjectAtIndex = class_getInstanceMethod(objc_getClass("__NSArrayI"), @selector(objectAtSafeIndex:));
    method_exchangeImplementations(oldObjectAtIndex, newObjectAtIndex);
    
    //替换可变数组方法
    Method oldMutableObjectAtIndex = class_getInstanceMethod(objc_getClass("__NSArrayM"), @selector(objectAtIndex:));
    Method newMutableObjectAtIndex =  class_getInstanceMethod(objc_getClass("__NSArrayM"), @selector(mutableObjectAtSafeIndex:));
    method_exchangeImplementations(oldMutableObjectAtIndex, newMutableObjectAtIndex);
}

- (id)objectAtSafeIndex:(NSUInteger)index
{
    if (index > self.count - 1 || !self.count) {
        @try {
            return [self objectAtSafeIndex:index];
        }
        @catch (NSException *exception) {
            NSLog(@"exception: %@", exception.reason);
            return nil;
        }
        
    }else {
        return [self objectAtSafeIndex:index];
    }
}

- (id)mutableObjectAtSafeIndex:(NSUInteger)index
{
    if (index > self.count - 1 || !self.count) {
        @try {
            return [self mutableObjectAtSafeIndex:index];
        }
        @catch (NSException *exception) {
            NSLog(@"exception: %@", exception.reason);
            return nil;
        }
        
    }else {
        return [self mutableObjectAtSafeIndex:index];
    }
}

@end