Mantle,JSONModel,MJExtension防崩溃能

Mantle,JSONModel,MJExtension防崩溃比较:
对于这样一条数据:

{
"firstName": "张", 
"lastName": "三", 
"age": 23,
"height": 172.3, 
 "weight": 51.2, 
"sex": true
}

客户端属性声明为:
@property (nonatomic, copy) NSString *age;

Mantle的模型赋值:

if (![obj validateValue:&validatedValue forKey:key error:error]) return NO;
if (forceUpdate || value != validatedValue) 
{
[obj setValue:validatedValue forKey:key];
}
return YES;

它是使用了KVC的- (BOOL)validateValue:(inout id __nullable * __nonnull)ioValue forKey:(NSString *)inKey error:(out NSError **)outError;方法来验证要赋的值的类型是否和key的类型是否匹配.该方法默认会调用a validator method whose name matches the pattern -validate<Key>:error:.因此我们还需要在模型里面写一个这样的方法:

-(BOOL)validateAge:(id *)ioValue error:(NSError * __autoreleasing *)outError
{
    if ([*ioValue isKindOfClass:[NSNumber class]])
    {
        return YES;
    }
    return NO;
}

如果没写默认返回YES.Mantle貌似并没有帮我们做这么一步,所以如果你自己没写的话,那么上述验证的方法会返回YES.好的程序不应该总是期望服务器端永远都返回正确的东西,然而我们又无法知道服务器哪些字段会返回和我们不一致的类型.难道每一个属性都要写一个-validate<Key>:error:来判断?个人认为在这一点上Mantle做的很鸡肋.如果你没写-validate<Key>:error:而碰巧服务器端返回一个数字类型,那么你的程序很有可能会崩溃.

对于JSONModel的模型赋值:

//check for custom transformer
BOOL foundCustomTransformer = NO;
if ([valueTransformer respondsToSelector:selector]) {
    foundCustomTransformer = YES;
} else {
    //try for hidden custom transformer
    selectorName = [NSString stringWithFormat:@"__%@",selectorName];
    selector = NSSelectorFromString(selectorName);
    if ([valueTransformer respondsToSelector:selector]) {
        foundCustomTransformer = YES;
    }
}

//check if there's a transformer with that name
if (foundCustomTransformer) {

    //it's OK, believe me...
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
    //transform the value
    jsonValue = [valueTransformer performSelector:selector withObject:jsonValue];
#pragma clang diagnostic pop

    if (![jsonValue isEqual:[self valueForKey:property.name]]) {
        [self setValue:jsonValue forKey: property.name];
    }

} else {

    // it's not a JSON data type, and there's no transformer for it
    // if property type is not supported - that's a programmer mistake -> exception
    @throw [NSException exceptionWithName:@"Type not allowed"
                                   reason:[NSString stringWithFormat:@"%@ type not supported for %@.%@", property.type, [self class], property.name]
                                 userInfo:nil];
    return NO;
}

可以看到它有做一个转换,对于一般的服务端数字,客户端NSString,或服务器端字符,客户端NSNumber,这样比较简单的转换,JSONModel已经帮我们实现好了,但是如果服务器端返回一个数组,但是客户端是NSString,那么这需要我们自己按照它的格式去写一个转换的方法,如果没写的话,JSONModel会抛出一个异常.然而通常我们需要服务器端传错了,我们客户端应该不崩溃,而是将对应的字段赋值为nil.

对于MJExtension的模型赋值:
由于MJ的考虑的情况比较全面,代码较多,有兴趣的可以自己去看,这里只截取最后一部分:

// value和property类型不匹配
if (propertyClass && ![value isKindOfClass:propertyClass])
{
value = nil;
}

可以看到如果类型不匹配那么对应的属性将被赋值为nil.而这些不需要我们写任何代码,可以的.最为厉害的就是当服务器传字符,客户端为NSUInteger类型时,Mantle,JSONModel都会崩溃,而MJ不会崩溃,且正确转换.
综上防崩溃最强的当属MJExtension,如果服务器端开发人员很菜的话强烈推荐使用MJExtension.