NLog，访问自定义目标中的布局渲染器

问题描述

我正在创建一个自定义目标，但我发现无法从 Write 方法访问布局渲染器值，例如 aspnet-traceidentifier https://github.com/NLog/NLog/wiki/AspNetTraceIdentifier-Layout-Renderer。

这是我使用的代码：

[Target("CustomTarget")]
public sealed class CustomTarget : AsyncTaskTarget
{
    protected override async Task WriteAsyncTask(LogEventInfo logEvent,CancellationToken token)
    {
        var layout = new NLog.Layouts.SimpleLayout("${aspnet-traceidentifier}");
        string logMessage = this.Layout.Render(logEvent);

        string identifier = layout.Render(logEvent);
        // identifier is empty here...
        
        identifier = RenderLogEvent("${aspnet-traceidentifier}",logEvent);
        
        // identifier is empty here...
    }  
}

解决方法

也许是这样的：

    [Target("CustomTarget")] 
    public sealed class CustomTarget : AsyncTaskTarget
    { 
        public CustomTarget()
        {
            this.CorrelationId = "${aspnet-traceidentifier}";
        }
 
        public Layout CorrelationId { get; set; }
 
        protected override Task WriteAsyncTask(LogEventInfo logEvent,CancellationToken token)
        { 
            string logMessage = this.RenderLogEvent(this.Layout,logEvent); 
            string correlationId = this.RenderLogEvent(this.CorrelationId,logEvent); 

            // TODO - write message
        } 
    } 

另请参阅编写自定义 NLog 目标的教程：https://github.com/NLog/NLog/wiki/How-to-write-a-custom-async-target