成员访问中的问号在 C# 中是什么意思?

What does the question mark in member access mean in C#?(成员访问中的问号在 C# 中是什么意思?)

问题描述

谁能给我解释一下下面代码中成员访问中的问号是什么意思?

Can someone please explain to me what does the question mark in the member access in the following code means?

它是标准 C# 的一部分吗?尝试在 Xamarin Studio 中编译此文件时出现解析错误.

Is it part of standard C#? I get parse errors when trying to compile this file in Xamarin Studio.

this.AnalyzerLoadFailed?.Invoke(this, new AnalyzerLoadFailureEventArgs(AnalyzerLoadFailureEventArgs.FailureErrorCode.NoAnalyzers, null, null));

AnalyzerFileReference.cs 行195

推荐答案

Null Propagation operator在C#6中引入，只有对象this.AnalyzerLoadFailed不为null时才会调用该方法:

this.AnalyzerLoadFailed?.Invoke(this, new AnalyzerLoadFailureEventArgs(AnalyzerLoadFailureEventArgs.FailureErrorCode.NoAnalyzers, null, null));

if( this.AnalyzerLoadFailed != null)
    this.AnalyzerLoadFailed.Invoke(this, new AnalyzerLoadFailureEventArgs(AnalyzerLoadFailureEventArgs.FailureErrorCode.NoAnalyzers, null, null));

我也曾经在 c# 6 中写过这个即将推出的特性 <强>这里

i also once wrote about this upcoming feature in c# 6 here

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