检查表达式是否有效 | 表达式是否有效

本文介绍了检查表达式是否有效的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我要验证表达式是否有效.我正在尝试使用以下代码:

I want to validate expression is valid or not. And I am trying this using following code :

let equationString = "12+6+"

do {
    let expr =  try NSExpression(format: equationString)
    if let result = expr.expressionValue(with: nil, context: nil) as? NSNumber {
        let x = result.doubleValue
        print(x)
    } else {
        print("failed")
    }
}
catch {
    print("failed")
}

我使用了try-catch语句，但是仍然在这里崩溃.有什么解决办法吗?

I have used try-catch statement, but still I am getting crash here. Is there any solution for this?

任何帮助将不胜感激.

推荐答案

您可以尝试使用它:

let equationString = "12+6+"//"12*/6+10-5/2"

do {
    try TryCatch.try({
        let expr = NSExpression(format: equationString)
        if let result = expr.expressionValue(with: nil, context: nil) as? NSNumber {
            let x = result.doubleValue
            print(x)
        } else {
            print("failed")
        }
    })
} catch {
    print("Into the catch.....")
    // Handle error here
}

TryCatch.h :

+ (BOOL)tryBlock:(void(^)(void))tryBlock
           error:(NSError **)error;

TryCatch.m :

@implementation TryCatch

+ (BOOL)tryBlock:(void(^)(void))tryBlock
           error:(NSError **)error
{
    @try {
        tryBlock ? tryBlock() : nil;
    }
    @catch (NSException *exception) {
        if (error) {
            *error = [NSError errorWithDomain:@"com.something"
                                         code:42
                                     userInfo:@{NSLocalizedDescriptionKey: exception.name}];
        }
        return NO;
    }
    return YES;
}

@end

这篇关于检查表达式是否有效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！