iOS项目开发中，对后台返回数据为<null>时候的处理,避免取值产生程序崩溃问题

大致实现思路就是循环遍历做比较，如果发现是NSNull类型的就把值改为空字符串；这样的好处就是当数据请求回来，删除一下数据里面为<null>类型的东西，避免在直接取的时候产生程序崩溃问题；

两个方法，一个返回NSArray，一个是NSDictionary，根据需求选择

.h 文件

/**
 *  服务器返回的数据为<null>时的处理
 *
 *  @param dic 经处理过后的数据，数据类型为字典，避免直接取数据时出现程序崩溃现象。
 */
- (NSDictionary *)deleteEmpty:(NSDictionary *)dic;

/**
 *  服务器返回的数据为<null>时的处理
 *
 *  @param dic 经处理过后的数据，数据类型为数组，避免直接取数据时出现程序崩溃现象。
 */
- (NSArray *)deleteEmptyArr:(NSArray *)arr;

.m 文件

@implementation NSObject (DeleteArrOrDeleteDicBothNull)

- (NSDictionary *)deleteEmpty:(NSDictionary *)dic
{
    NSMutableDictionary *mdic = [[NSMutableDictionary alloc] initWithDictionary:dic];
    NSMutableArray *set = [[NSMutableArray alloc] init];
    NSMutableDictionary *dicSet = [[NSMutableDictionary alloc] init];
    NSMutableDictionary *arrSet = [[NSMutableDictionary alloc] init];
    for (id obj in mdic.allKeys)
    {
        id value = mdic[obj];
        if ([value isKindOfClass:[NSDictionary class]])
        {
            NSDictionary *changeDic = [self deleteEmpty:value];
            [dicSet setObject:changeDic forKey:obj];
        }
        else if ([value isKindOfClass:[NSArray class]])
        {
            NSArray *changeArr = [self deleteEmptyArr:value];
            [arrSet setObject:changeArr forKey:obj];
        }
        else
        {
            if ([value isKindOfClass:[NSNull class]]) {
                [set addObject:obj];
            }
        }
    }
    for (id obj in set)
    {
        mdic[obj] = @"";
    }
    for (id obj in dicSet.allKeys)
    {
        mdic[obj] = dicSet[obj];
    }
    for (id obj in arrSet.allKeys)
    {
        mdic[obj] = arrSet[obj];
    }
    
    return mdic;
}

- (NSArray *)deleteEmptyArr:(NSArray *)arr
{
    NSMutableArray *marr = [NSMutableArray arrayWithArray:arr];
    NSMutableArray *set = [[NSMutableArray alloc] init];
    NSMutableDictionary *dicSet = [[NSMutableDictionary alloc] init];
    NSMutableDictionary *arrSet = [[NSMutableDictionary alloc] init];
    
    for (id obj in marr)
    {
        if ([obj isKindOfClass:[NSDictionary class]])
        {
            NSDictionary *changeDic = [self deleteEmpty:obj];
            NSInteger index = [marr indexOfObject:obj];
            [dicSet setObject:changeDic forKey:@(index)];
        }
        else if ([obj isKindOfClass:[NSArray class]])
        {
            NSArray *changeArr = [self deleteEmptyArr:obj];
            NSInteger index = [marr indexOfObject:obj];
            [arrSet setObject:changeArr forKey:@(index)];
        }
        else
        {
            if ([obj isKindOfClass:[NSNull class]]) {
                NSInteger index = [marr indexOfObject:obj];
                [set addObject:@(index)];
            }
        }
    }
    for (id obj in set)
    {
        marr[(int)obj] = @"";
    }
    for (id obj in dicSet.allKeys)
    {
        int index = [obj intValue];
        marr[index] = dicSet[obj];
    }
    for (id obj in arrSet.allKeys)
    {
        int index = [obj intValue];
        marr[index] = arrSet[obj];
    }
    return marr;
}

@end