在应用 NSPredicate 时转换 NSDictionary 值？
我有一个 NSDictionary 对象数组。 这些字典是从 JSON 文件解析的。 NSDictionary 中的所有值对象都是 NSString 类型，其中一个键称为“distanceInMeters”。
我计划使用 NSPredicate 来过滤这些数组，所以我是这样开始的：
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(distanceInMeters <= %f)", newValue];
NSArray *newArray = [oldArray filteredArrayUsingPredicate:predicate];
我相信如果“distanceInMeters”键的值是 NSNumber，那么这会起作用，但因为我从 JSON 文件中获得它，所以一切都是 NSString。 上面给出了这个错误：****** -[NSCFNumber length]: unrecognized selector sent to instance 0x3936f00***
这是有道理的，因为我刚刚尝试将 NSString 视为 NSNumber。
有没有办法在过滤字典时从字典中转换值，或者可能有一种完全不同的方法来解决这个问题？
希望有人能帮助我:)
I have an Array of NSDictionary objects.
These Dictionaries are parsed from a JSON file.
All value objects in the NSDictionary are of type NSString, one key is called "distanceInMeters".
I had planned on filtering these arrays using an NSPredicate, so I started out like this:
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(distanceInMeters <= %f)", newValue];
NSArray *newArray = [oldArray filteredArrayUsingPredicate:predicate];
I believe this would have worked if the value for the "distanceInMeters" key was an NSNumber, but because I have it from a JSON file everything is NSStrings.
The above gives this error:****** -[NSCFNumber length]: unrecognized selector sent to instance 0x3936f00***
Which makes sense as I had just tried to treat an NSString as an NSNumber.
Is there a way to cast the values from the dictionary while they are being filtered, or maybe a completely different way of getting around this?
Hope someone can help me :)
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试试这个：
Try this:
你的问题不是谓词；而是谓词。您的问题是您正在处理
NSString对象，而不是处理NSNumber对象。我会首先将时间集中在将它们更改为 NSNumbers 上，然后验证它是否不起作用。仅供参考，JSON 框架 会自动将数字解析为
NSNumbers...Your problem isn't the predicate; your problem is that you're dealing with
NSStringobjects instead of dealing withNSNumberobjects. I would focus my time on changing them toNSNumbersfirst, and then verify that it's not working.FYI, the JSON Framework does automatic parsing of numbers into
NSNumbers...