2018年4月17日
1.效果

NSArray *arr = @[@1];
    arr[1];
    
    NSMutableArray *mArr = @[@2].mutableCopy;
    mArr[1];

2018-04-17 10:36:46.924 quanqunahuli[13015:365882] 不可数组越界了
2018-04-17 10:36:49.197 quanqunahuli[13015:365882] 可变数组越界了

2.实现

#import <Foundation/Foundation.h>
@interface NSArray (Wgarray)
@end

#import "NSArray+Wgarray.h"
#import <objc/message.h>
@implementation NSArray (Wgarray)
+ (void)load {
    [super load];
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        // 替换不可变数组中的方法 objectAtIndex
        Method oldObjectAtIndex = class_getInstanceMethod(objc_getClass("__NSArrayI"), @selector(objectAtIndex:));
        Method newObjectAtIndex = class_getInstanceMethod(objc_getClass("__NSArrayI"), @selector(newObjectAtIndex:));
        method_exchangeImplementations(oldObjectAtIndex, newObjectAtIndex);
        // 替换不可变数组中的方法 []调用的方法
        Method objectAtIndexedSubscript = class_getInstanceMethod(objc_getClass("__NSArrayI"), @selector(objectAtIndexedSubscript:));
        Method newObjectAtIndexedSubscript = class_getInstanceMethod(objc_getClass("__NSArrayI"), @selector(newObjectAtIndexedSubscript:));
        method_exchangeImplementations(objectAtIndexedSubscript, newObjectAtIndexedSubscript);
        // 替换可变数组中的方法 objectAtIndex
        Method oldMObjectAtIndex = class_getInstanceMethod(objc_getClass("__NSArrayM"), @selector(objectAtIndex:));
        Method newMObjectAtIndex = class_getInstanceMethod(objc_getClass("__NSArrayM"), @selector(newMutableObjectAtIndex:));
        method_exchangeImplementations(oldMObjectAtIndex, newMObjectAtIndex);
        // 替换可变数组中的方法  []调用的方法
        Method oldMMutableObjectAtIndex = class_getInstanceMethod(objc_getClass("__NSArrayM"), @selector(objectAtIndexedSubscript:));
        Method newMMutableObjectAtIndex = class_getInstanceMethod(objc_getClass("__NSArrayM"), @selector(newMutableObjectAtIndexedSubscript:));
        method_exchangeImplementations(oldMMutableObjectAtIndex, newMMutableObjectAtIndex);
    });
}
- (id)newObjectAtIndex:(NSUInteger)index {
    if (index > self.count - 1 || !self.count) {
        @try {
            return [self newObjectAtIndex:index];
        } @catch (NSException *exception) {
            NSLog(@"不可数组越界了");
            return nil;
        } @finally {
        }
    } else {
        return [self newObjectAtIndex:index];
    }
}
- (id)newObjectAtIndexedSubscript:(NSUInteger)index {
    if (index > self.count - 1 || !self.count) {
        @try {
            return [self newObjectAtIndexedSubscript:index];
        } @catch (NSException *exception) {
            NSLog(@"不可数组越界了");
            return nil;
        } @finally {
        }
    } else {
        return [self newObjectAtIndexedSubscript:index];
    }
}
- (id)newMutableObjectAtIndex:(NSUInteger)index {
    if (index > self.count - 1 || !self.count) {
        @try {
            return [self newMutableObjectAtIndex:index];
        } @catch (NSException *exception) {
            NSLog(@"可变数组越界了");
            return nil;
        } @finally {
        }
    } else {
        return [self newMutableObjectAtIndex:index];
    }
}
- (id)newMutableObjectAtIndexedSubscript:(NSUInteger)index {
    if (index > self.count - 1 || !self.count) {
        @try {
            return [self newMutableObjectAtIndexedSubscript:index];
        } @catch (NSException *exception) {
            NSLog(@"可变数组越界了");
            return nil;
        } @finally {
        }
    }
    else{
        return [self newMutableObjectAtIndexedSubscript:index];
    }
}
@end

ps：如下用法ios系统9.3（含）以下会奔溃，初步定位为 是继承类导致替换方法混乱导致（按上面方法都写在父类里面解决）

#import <Foundation/Foundation.h>
@interface NSArray (Wgarray)
@end
@interface NSMutableArray (Wgarray)
@end

#import "NSArray+Wgarray.h"
#import <objc/message.h>
@implementation NSArray (Wgarray)
+(void)load{
    [super load];
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class class = NSClassFromString(@"__NSArrayI");
        Method oldMethod = class_getInstanceMethod(class, @selector(objectAtIndexedSubscript:));
        Method newMethod = class_getInstanceMethod(class, @selector(wg_objectAtIndexedSubscript:));
        if (oldMethod && newMethod) {
            method_exchangeImplementations(oldMethod, newMethod);
        }
    });
}
- (id)wg_objectAtIndexedSubscript:(NSUInteger)index{
    if (!self.count || self.count - 1 < index) {
        TRACELOG(@"objectAtIndexedSubscript越界");
        return nil;
    }else{
        id obj = [self wg_objectAtIndexedSubscript:index];
        return obj;
    }
}
@end
@implementation NSMutableArray (Wgarray)
+(void)load{
    [super load];
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        //注意：他的确定可以从崩溃日至那里来确定，这个__NSArrayM类名的确认是从崩溃日志'*** -[__NSArrayM objectAtIndexedSubscript:]: index 6 beyond bounds [0 .. 2]'来确定的
        Class class = NSClassFromString(@"__NSArrayM");
        Method oldMethod = class_getInstanceMethod(class, @selector(objectAtIndexedSubscript:));
        Method newMethod = class_getInstanceMethod(class, @selector(wg_objectAtIndexedSubscript:));
        if (oldMethod && newMethod) {
            method_exchangeImplementations(oldMethod, newMethod);
        }
    });
}
- (id)wg_objectAtIndexedSubscript:(NSUInteger)index{
    if (!self.count || self.count - 1 < index) {
        TRACELOG(@"objectAtIndexedSubscript可变数组越界");
        return nil;
    }else{
        id obj = [self wg_objectAtIndexedSubscript:index];
        return obj;
    }
}
@end

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