成员访问中的问号在C#中意味着什么？

Question

有人可以向我解释以下代码中成员访问中的问号是什么意思？

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.

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

AnalyzerFileReference.cs第195行

Answer 1

它是C#6中引入的Null Propagation运算符,只有当object 不为null 时才调用该方法:this.AnalyzerLoadFailed

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

等于:

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

参见C#6.0 - Null Propagation Operator,你也可以在这里看到

我也曾在这里写过关于c#6即将推出的这个功能

Answer 2

在C#版本6中,它将是简写

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