如何在int.Parse中修复此ArgumentNullException?

问题描述

这是.cs文件在Mono中可以正常运行:

This is the .cs file runs fine in Mono:

using System;

public class HelloWorld
{
    static public void Main ()
    {
    Console.WriteLine("Enter a number");

    int UserNumber = int.Parse(Console.ReadLine());

    Console.WriteLine("Your number is: " + UserNumber);
    }
}

我在Xamarin中打开了此Test.cs文件，该文件工作正常.然后，选择运行">不调试开始"，这些错误会在显示面板中弹出:

I opened this Test.cs file in Xamarin, which worked properly. Then I choose 'Run' > 'Start Without Debugging' and these errors pop up in the display panel:

Enter a number

Unhandled Exception:
System.ArgumentNullException: Argument cannot be null.
Parameter name: String
  at System.Number.StringToNumber (System.String str, NumberStyles options, System.NumberBuffer& number, System.Globalization.NumberFormatInfo info, Boolean parseDecimal) [0x00054] in /private/tmp/source-mono-mac-4.0.0-branch-c5sr2/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.2/external/referencesource/mscorlib/system/number.cs:1084
  at System.Number.ParseInt32 (System.String s, NumberStyles style, System.Globalization.NumberFormatInfo info) [0x00014] in /private/tmp/source-mono-mac-4.0.0-branch-c5sr2/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.2/external/referencesource/mscorlib/system/number.cs:755
  at System.Int32.Parse (System.String s) [0x00000] in /private/tmp/source-mono-mac-4.0.0-branch-c5sr2/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.2/external/referencesource/mscorlib/system/int32.cs:140
  at HelloWorld.Main () [0x0000b] in /Users/Yardenbourg/Desktop/Test.cs:9
[ERROR] FATAL UNHANDLED EXCEPTION: System.ArgumentNullException: Argument cannot be null.
Parameter name: String
  at System.Number.StringToNumber (System.String str, NumberStyles options, System.NumberBuffer& number, System.Globalization.NumberFormatInfo info, Boolean parseDecimal) [0x00054] in /private/tmp/source-mono-mac-4.0.0-branch-c5sr2/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.2/external/referencesource/mscorlib/system/number.cs:1084
  at System.Number.ParseInt32 (System.String s, NumberStyles style, System.Globalization.NumberFormatInfo info) [0x00014] in /private/tmp/source-mono-mac-4.0.0-branch-c5sr2/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.2/external/referencesource/mscorlib/system/number.cs:755
  at System.Int32.Parse (System.String s) [0x00000] in /private/tmp/source-mono-mac-4.0.0-branch-c5sr2/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.2/external/referencesource/mscorlib/system/int32.cs:140
  at HelloWorld.Main () [0x0000b] in /Users/Yardenbourg/Desktop/Test.cs:9
The application was terminated by a signal: SIGHUP

我不确定这是什么问题.可能与这条线有关吗?

I am not sure what the problem here is. Could it be to do with this line?

int UserNumber = int.Parse(Console.ReadLine());

推荐答案

读取堆栈跟踪，它表示Parse方法已传递了null参数，但不能为null.尝试拆分读取行并进行解析，然后确保该行不为null或为空.

Read the stack trace, it says the method of Parse was passed a parameter of null, but it cannot be null. Try splitting the read line and the parsing, and then making sure the line is not null or empty.

public class HelloWorld
{
    static public void Main ()
    {
    Console.WriteLine("Enter a number");
    String input = Console.ReadLine();
    int UserNumber = 0;
    if(input != null && input != "")
    {
        UserNumber = int.Parse(input);
    }

    Console.WriteLine("Your number is: " + UserNumber);
    }
}

像这样拆分代码，使其更易于阅读和调试.

Splitting up code like this makes it easier to read and easier to debug.

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