通过方法转换，将array添加元素的方法进行转换，避免添加nil对象时出现crash情况。

#import <Foundation/Foundation.h>

@interface NSMutableArray (RunTime)

@end

#import "NSMutableArray+RunTime.h"
#import <objc/runtime.h>

@implementation NSMutableArray (RunTime)

#pragma mark - 方法替换

+ (void)load
{
    // 方法1
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        // 无效
//        Class class = [self class];
        // 有效
        Class class = NSClassFromString(@"__NSArrayM");
        
        SEL originalSelector = @selector(addObject:);
        SEL swizzledSelector = @selector(addObjectSafe:);

        Method originalMethod = class_getInstanceMethod(class, originalSelector);
        Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);

        // judge the method named  swizzledMethod is already existed.
        BOOL didAddMethod = class_addMethod(class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
        // if swizzledMethod is already existed.
        if (didAddMethod)
        {
            class_replaceMethod(class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
        }
        else
        {
            method_exchangeImplementations(originalMethod, swizzledMethod);
        }
    });
    
    // 方法2
    // 无效（异常：Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSArrayM insertObject:atIndex:]: object cannot be nil'）
//        Class class = [self class];
    // 有效
//    Class class = NSClassFromString(@"__NSArrayM");
//    Method oldMethod = class_getInstanceMethod(class, @selector(addObject:));
//    Method newMethod = class_getInstanceMethod(class, @selector(addObjectSafe:));
//    method_exchangeImplementations(oldMethod, newMethod);
}

- (void)addObjectSafe:(id)anObject
{
    if (anObject)
    {
        [self addObjectSafe:anObject];
        NSLog(@"添加成功");
    }
    else
    {
        NSLog(@"添加失败，不能添加 nil 对象");
    }
}

@end