NSExpression捕获无效的参数 [英] NSExpression catch invalid arguments

问题描述

我正在使用NSExpression评估数学字符串，并且效果很好.但是，我想提供一种在输入字符串无效(例如"3 ++ 2")时捕获错误的方法.有没有办法解决此问题，而不是由于"NSInvalidArgumentException"而导致应用程序终止.抱歉，我对Objective-C还是陌生的.我现在使用的代码是:

I am using NSExpression to evaluate a mathematical string and it works great. However I want to have a way of catching an error when the input string is invalid, such as "3++2". Is there a way to go about doing this instead of the application terminating due to 'NSInvalidArgumentException'. Sorry, I am fairly new to objective-c. The code I am using now is:

NSExpression *exp = [NSExpression expressionWithFormat: string];
NSNumber *result = [exp expressionValueWithObject:nil context:nil];
answer = [result stringValue];

推荐答案

我认为NSExpression不是这里工作的正确工具.该类是Cocoa谓词系统的一部分，被设计为仅接受格式正确的输入.

I think NSExpression is not the right tool for the job here. The class is part of the Cocoa predicate system and was designed to only accept well-formatted input.

我建议您寻找合适的数学解析器.我相信 GCMathParser 是一个不错的选择.还有 DDMathParser .

I suggest you look for a proper math parser. I believe GCMathParser is a good choice. There's also DDMathParser.

如果您坚持使用NSExpression，则可以捕获如下异常:

If you insist on using NSExpression, you can catch the exception like this:

@try {
  // the code that potentially raises an NSInvalidArgumentException
} @catch (NSException *exception) {
  if ([[exception name] isEqualToString:NSInvalidArgumentException]) {
    // your error handling
  }
}

但是，请注意，这是不好的做法. Objective-C中的异常仅应用于捕获意外的运行时错误.您的示例不符合条件.

Be advised, however, that this is bad practice. Exceptions in Objective-C should only be used to catch unexpected runtime errors. Your example does not qualify.

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