NSNumberFormatter numberFromString十进制数

问题描述

我试图用 NSNumberFormatter 解析 NSString ，如下所示。

  NSNumberFormatter * myFormatter = [[[NSNumberFormatter alloc] init]; 
 NSNumber * myNumber = [myFormatter numberFromString：@42.00000]; 
  

numberFromString 返回

小数点（.00000）使得模拟器中的返回值为nil，而不是在设备上。设备因为解析42（没有小数）工作正常（在模拟器和设备上）。

我使用NSNumberFormatter的原因是因为像如果字符串不是一个有效的数字（这是对我在这里：p）返回 nil 。 NSString doubleValue 不提供这种行为。此外， NSDecimalNumber decimalNumberWithString 不执行此作业，因为 [NSDecimalNumber decimalNumberWithString：@4a2 .00000] 返回4。

任何想法为什么这不会在设备上工作？

这是区域设置吗？我尝试设置 myFormatter.numberStyle = NSNumberFormatterNoStyle 和 NSNumberFormatterDecimalStyle 但它什么也不更改。

NSNumberFormatter 的小数分隔符是
区域设置依赖。如果你有一个固定的输入格式，以点为小数分隔符
你可以设置POSIX locale：

  NSNumberFormatter * myFormatter = [[NSNumberFormatter alloc] init]; 
 [myFormatter setLocale：[NSLocale localeWithLocaleIdentifier：@en_US_POSIX]]; 
 NSNumber * myNumber = [myFormatter numberFromString：@42.00000]; 
  

或者，您可以使用 NSScanner 双值，例如在此处描述
：

I'm trying to parse a NSString with a NSNumberFormatter like following.

NSNumberFormatter *myFormatter = [[[NSNumberFormatter alloc] init];
NSNumber *myNumber = [myFormatter numberFromString:@"42.00000"];

numberFromString returns a NSNumber object in the simulator but not on a device.

The decimals (.00000) are causing the return value to be nil on a device because parsing 42 (without the decimals) works just fine (both in the simulator and on a device).

The reason I'm using a NSNumberFormatter is because is like how it returns nil if the string is not a valid number (which is working against me here :p). NSString doubleValue does not provide this kind of behaviour. Also, NSDecimalNumber decimalNumberWithString doesn't do the job because [NSDecimalNumber decimalNumberWithString:@"4a2.00000"] returns 4.

Any ideas why this would not work on a device?

Is it the locale? I tried setting myFormatter.numberStyle = NSNumberFormatterNoStyle and NSNumberFormatterDecimalStyle but it changes nothing.

解决方案

As @rmaddy already said in a comment, the decimal separator of NSNumberFormatter islocale dependent. If you have a fixed input format with the dot as decimal separator,you can set the "POSIX locale":

NSNumberFormatter *myFormatter = [[NSNumberFormatter alloc] init];
[myFormatter setLocale:[NSLocale localeWithLocaleIdentifier:@"en_US_POSIX"]];
NSNumber *myNumber = [myFormatter numberFromString:@"42.00000"];

Alternatively, you can use NSScanner to parse a double value, as e.g. describedhere: parsing NSString to Double

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