How-To: Enable Internal Logging Based on Your Hosting Environment

Uno.Extensions.Logging provides logging capabilities tailored to your target platform. It allows the recording of events for XAML layout, Uno-internal messages, and custom events with severity and verbosity levels of your choice.

Step-by-step

Important

This guide assumes your application has already opted into logging. To find out how to do this, refer to the tutorial here

1. Enable Uno internal logging

Add Logging to the <UnoFeatures> property in the Class Library (.csproj) file. If you already have Extensions in <UnoFeatures>, then Logging is already installed, as its dependencies are included with the Extensions feature.
```
<UnoFeatures>
    Material;
+   Logging;
    Toolkit;
    MVUX;
</UnoFeatures>
```

To log Uno-internal messages, you first need to call UseLogging() on the IHost instance, passing true in for the enableUnoLogging parameter:

private IHost Host { get; set; }

protected override void OnLaunched(LaunchActivatedEventArgs e)
{
    var appBuilder = this.CreateBuilder(args)
        .Configure(host => {
            host
            .UseLogging(enableUnoLogging: true)
        });

    Host = appBuilder.Build();

2. Set verbosity level of XAML logging

There are multiple log levels that correspond to differing degrees of severity:

Level	Description
Trace	Used for parts of a method to capture a flow.
Debug	Used for diagnostics information.
Information	Used for general successful information. Generally the default minimum.
Warning	Used for anything that can potentially cause application oddities. Automatically recoverable.
Error	Used for anything that is fatal to the current operation but not to the whole process. Potentially recoverable.
Critical	Used for anything that is forcing a shutdown to prevent data loss or corruption. Not recoverable.

To increase the verbosity of the events recorded when using the development hosting environment, you can adjust the minimum levels as well as those for the XAML layout.

Conditionally enable the recording of debug events depending on the hosting environment:

private IHost Host { get; set; }

protected override void OnLaunched(LaunchActivatedEventArgs e)
{
    var appBuilder = this.CreateBuilder(args)
        .Configure(host => {
            host
#if DEBUG
            .UseEnvironment(Environments.Development)
#endif
            .UseLogging(configure:
                (context, services) =>
                    services.SetMinimumLevel(
                    context.HostingEnvironment.IsDevelopment() ?
                        LogLevel.Trace :
                        LogLevel.Error)
                    )
        });

    Host = appBuilder.Build();
...

3. Enable specific types of internal logging

Setting the XAML Log Level

Filter out messages recorded for specific XAML types by setting the XAML log level.

To adjust the verbosity of logged events raised by a set of XAML-related types, you should call the XamlLogLevel() extension method on the ILoggingBuilder instance. The following example shows how to set the XAML log level to Information:

protected override void OnLaunched(LaunchActivatedEventArgs e)
{
    var appBuilder = this.CreateBuilder(args)
        .Configure(host => {
            host.UseLogging(
                builder => {
                    builder.XamlLogLevel(LogLevel.Information);
                });
        });
...

Setting the Layout Log Level

The layout log level can be used to filter messages recorded from a set of layout-related types.

To set this up, call the XamlLayoutLogLevel() extension method on the ILoggingBuilder instance. The following example shows how to set the XAML layout log level to Information:

protected override void OnLaunched(LaunchActivatedEventArgs e)
{
    var appBuilder = this.CreateBuilder(args)
        .Configure(host => {
            host.UseLogging(
                builder => {
                    builder.XamlLayoutLogLevel(LogLevel.Information);
                });
        });
    ...
}

4. Testing the logging configuration

Run the application in debug mode and open the Output window in Visual Studio.
Since you have configured Uno-internal logging, messages with a severity level of Information or higher will now be recorded for the specified categories.