iOS 好用的防止后台返回数据为Null时崩溃的过滤方法

#pragma mark - 公有方法，直接使用
//类型识别:将所有的NSNull类型转化成@""
+(id)changeType:(id)myObj
{
if ([myObj isKindOfClass:[NSDictionary class]])    {
 return [self nullDic:myObj];
}    else if([myObj isKindOfClass:[NSArray class]])    {
 return [self nullArr:myObj];
}    else if([myObj isKindOfClass:[NSString class]])    {
 return [self stringToString:myObj];    }
else if([myObj isKindOfClass:[NSNull class]])    {
 return [self nullToString];
}
else    {
 return myObj;
}}
#pragma mark - 私有方法
//将NSDictionary中的Null类型的项目转化成@""
+(NSDictionary *)nullDic:(NSDictionary *)myDic
{
NSArray *keyArr = [myDic allKeys];
NSMutableDictionary *resDic = [[NSMutableDictionary alloc]init];
for (int i = 0; i < keyArr.count; i ++)    {
 id obj = [myDic objectForKey:keyArr[i]];
 obj = [self changeType:obj];
 [resDic setObject:obj forKey:keyArr[i]];
}
return resDic;
}
//将NSArray中的Null类型的项目转化成@""
+(NSArray *)nullArr:(NSArray *)myArr
{
NSMutableArray *resArr = [[NSMutableArray alloc] init];
for (int i = 0; i < myArr.count; i ++)    {
 id obj = myArr[i];
 obj = [self changeType:obj];
 [resArr addObject:obj];
}
return resArr;
}
//将NSString类型的原路返回
+(NSString *)stringToString:(NSString *)string
{
return string;
}
//将Null类型的项目转化成@""
+(NSString *)nullToString
{
return @"<NSNull>";
}