How can I use a RichTextBox as a NLog Target in a WPF application?

Question

I read the following posts but neither helped to just get the same efficient way of printing logs from NLog onto a RichTextBox control target as in Winforms.

How can I use NLog's RichTextBox Target in WPF application?

WPF: Binding RichTextBox to Logger Output

I also browsed the official forum but with no success (except suggestions to read the two above posts).

The idea would be to add the target as:

<target xsi:type="RichTextBox" name="console"
     layout="${longdate:useUTC=true}|${level:uppercase=true}|${logger}::${message}"
     autoScroll="true"
     maxLines="1000000"
     controlName="rtbConsole"
     formName="MyWPFWindowName"
     useDefaultRowColoringRules="true">
</target>

And within the WPF window with MyWPFWindowName as name, to add a RichTextBox control with rtbConsole. Even if I create the target programmatically after the winow has been loaded, it will not use the existing rtbConsole but create a new form.

So, your help is appreciated!

Answer 1

I created a custom NLog target and linked it to a text box.

public class NlogMemoryTarget : Target
{
    public Action<string> Log = delegate { };

    public NlogMemoryTarget (string name, LogLevel level)
    {
        LogManager.Configuration.AddTarget (name, this);

        LogManager.Configuration.LoggingRules.Add(new LoggingRule("*", level, this));//This will ensure that exsiting rules are not overwritten
        LogManager.Configuration.Reload(); //This is important statement to reload all applied settings

        //SimpleConfigurator.ConfigureForTargetLogging (this, level); //use this if you are intending to use only NlogMemoryTarget  rule
    }

    protected override void Write (AsyncLogEventInfo[] logEvents)
    {
        foreach (var logEvent in logEvents) {
            Write (logEvent);
        }
    }

    protected override void Write (AsyncLogEventInfo logEvent)
    {
        Write (logEvent.LogEvent);
    }

    protected override void Write (LogEventInfo logEvent)
    {
        Log (logEvent.FormattedMessage);
    }
}


public partial class MainWindow
{
    private NlogMemoryTarget _Target;

    public MainWindow ()
    {
        InitializeComponent ();

        this.Loaded += (s, e) => {
            _Target = new NlogMemoryTarget ("text box output", LogLevel.Trace);
            _Target.Log += log => LogText (log);
        };
    }

    private void LogText (string message)
    {
        this.Dispatcher.Invoke ((Action) delegate () {
            this.MessageView.AppendText (message + "\n");
            this.MessageView.ScrollToEnd ();
        });
    }
}

Answer 2

While this not really answer your question, but i believe this solution is better. An wpf control used to show NLog logs in listview. https://github.com/erizet/NlogViewer.

Answer 3

As @mafu's answer suggests:

[Create] a custom NLog [memory] Target and [link] it to a TextBox.

This sample will 'link it' via event and Event Handler delegates.

Define a NLog Memory Target as a Type

public class NlogMemoryTarget : Target
{
    public event EventHandler<string> OnLog;

    public NlogMemoryTarget(string name, LogLevel level) : this(name, level, level) {}
    public NlogMemoryTarget(string name, LogLevel minLevel, LogLevel maxLevel)
    {
        // important: we want LogManager.Configuration property assign behaviors \ magic to occur
        //   see: https://stackoverflow.com/a/3603571/1366179
        var config = LogManager.Configuration;

        // Add Target and Rule to their respective collections
        config.AddTarget(name, this);
        config.LoggingRules.Add(new LoggingRule("*", minLevel, maxLevel, this));

        LogManager.Configuration = config;
    }

    [Obsolete]
    protected override void Write(AsyncLogEventInfo[] logEvents)
    {
        foreach (var logEvent in logEvents) {
            Write(logEvent.LogEvent);
        }
    }

    protected override void Write(AsyncLogEventInfo logEvent)
    {
        Write(logEvent.LogEvent);
    }

    protected override void Write(LogEventInfo logEvent)
    {
        OnLog(this, logEvent.FormattedMessage);
    }

    // consider overriding WriteAsyncThreadSafe methods as well.
}

Usage in WPF Window Control

public partial class MainWindow
{
    private static readonly NLog.Logger logger = NLog.LogManager.GetCurrentClassLogger();

    private NlogMemoryTarget _nlogMemoryTarget;

    public MainWindow()
    {
        InitializeComponent();

        _nlogMemoryTarget = new NlogMemoryTarget("TextBoxOutput", LogLevel.Trace);
        _nlogMemoryTarget.OnLog += LogText;
    }

    private void LogText(object sender, string message)
    {
        this.MessageView.AppendText($"{message}\n");
        this.MessageView.ScrollToEnd();
    }

    private void DoSomething() {
       logger.Trace("DoSomething called!");
    }
}

When you call on DoSomething (or do logger.Trace), your overloaded methods in your memory target will execute - which raises the event OnLog. Since you assigned an event handler, LogText, to OnLog in the construction of MainWindow, it will execute.