NSPredicate：如何处理字符串作为数字？ [英] NSPredicate: how to treat strings as numbers?

问题描述

我正在iOS应用程序中使用sqlite上的核心数据构建一个复合NSPredicate来进行获取请求。一切已经工作正常，但我不能够包括最后一个条件。原因很简单：我需要检查值，存储为一个字符串，是否在一定的浮动范围内。问题是，按字母顺序基础检查条件，而不是根据其浮点值。这里是代码：

  NSString * conditionToBeAdded = [NSString stringWithFormat：@&&（％@> = \％@ \）&&&（％@< = \％@ \），propertyName，myMinFloat，propertyName，myMaxFloat]; 
 stringForPredicate = [stringForPredicate stringByAppendingString：conditionToBeAdded]; 
 NSPredicate * myPredicate = [NSPredicate predicateWithFormat：stringForPredicate]; 
  

有没有人知道如何构建一个NSPredicate对象能够检查字符串值作为数字，

解决方案

由于NSPredicates允许你使用匹配Key-Value Coding方法的一切，你可以调用NSStrings方法，如：intValue或floatValue

  NSString * conditionToBeAdded = [NSString stringWithFormat：@&&（propertyName.floatValue> =％f）&&（propertyName.floatValue< =％f），myMinFloat，myMaxFloat]; 
 stringForPredicate = [stringForPredicate stringByAppendingString：conditionToBeAdded]; 
 NSPredicate * myPredicate = [NSPredicate predicateWithFormat：stringForPredicate]; 
  

我希望有帮助。

I am building a compound NSPredicate to make a fetch request, using core data on sqlite, within iOS app. Everything already works fine, but I am not being able to include the last condition. The reason is quite simple: I need to check if the value, stored as a string, is within certain float bounds. The problem is that the conditions are checked on alphabetical order basis, and not according its float value. Here it is the code:

NSString * conditionToBeAdded = [NSString stringWithFormat:@" && (%@ >= \"""%@\""")  && (%@ <= \"""%@\""")", propertyName, myMinFloat, propertyName, myMaxFloat];
stringForPredicate = [stringForPredicate stringByAppendingString:conditionToBeAdded];  
NSPredicate * myPredicate = [NSPredicate predicateWithFormat:stringForPredicate];

Does anybody know how to build an NSPredicate object able to check string values as numbers, to be used within a coredata request?

Thank you.

解决方案

Since NSPredicates allow you to use everything which matches Key-Value Coding approach you can call on NSStrings methods like: intValue or floatValue

NSString * conditionToBeAdded = [NSString stringWithFormat:@" && (propertyName.floatValue >= %f )  && (propertyName.floatValue <= %f)", myMinFloat, myMaxFloat];
stringForPredicate = [stringForPredicate stringByAppendingString:conditionToBeAdded];  
NSPredicate * myPredicate = [NSPredicate predicateWithFormat:stringForPredicate];

I hope that helps.

这篇关于NSPredicate：如何处理字符串作为数字？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！