Logging

Virtually every production level application should utilize some form of logging. During development, especially when developing WASM applications where using a debugger can be more challenging, diagnostic logs can be invaluable for identifying issues. Once in production, capturing information about critical failures can be invaluable.

Logging in Uno

The Uno platform makes use of the Microsoft logging NuGet packages to provide comprehensive logging support.

Important

Due to current limitations regarding logging in WASM, Uno currently supports version 1.1.1 of the Microsoft.Extensions.Logging package and associated packages.

Configuring logging

The standard Uno template configures logging in the Shared project App.xaml.cs file.

In the Shared project and open the App.xaml.cs file.
Locate the App constructor and note that logging is configured first:
```
public App()
{
    ConfigureFilters(global::Uno.Extensions.LogExtensionPoint.AmbientLoggerFactory);
```
Notice that Uno provides a logger factory implementation.

Locate the ConfigureFilters method and review the code:

/// <summary>
/// Configures global logging
/// </summary>
/// <param name="factory"></param>
static void ConfigureFilters(ILoggerFactory factory)
{
    factory
        .WithFilter(new FilterLoggerSettings
            {
                { "Uno", LogLevel.Warning },
                { "Windows", LogLevel.Warning },

                // Debug JS interop
                // { "Uno.Foundation.WebAssemblyRuntime", LogLevel.Debug },

                // Generic XAML events
                // { "Windows.UI.Xaml", LogLevel.Debug },
                // { "Windows.UI.Xaml.VisualStateGroup", LogLevel.Debug },
                // { "Windows.UI.Xaml.StateTriggerBase", LogLevel.Debug },
                // { "Windows.UI.Xaml.UIElement", LogLevel.Debug },

                // Layouter specific messages
                // { "Windows.UI.Xaml.Controls", LogLevel.Debug },
                // { "Windows.UI.Xaml.Controls.Layouter", LogLevel.Debug },
                // { "Windows.UI.Xaml.Controls.Panel", LogLevel.Debug },
                // { "Windows.Storage", LogLevel.Debug },

                // Binding related messages
                // { "Windows.UI.Xaml.Data", LogLevel.Debug },

                // DependencyObject memory references tracking
                // { "ReferenceHolder", LogLevel.Debug },

                // ListView-related messages
                // { "Windows.UI.Xaml.Controls.ListViewBase", LogLevel.Debug },
                // { "Windows.UI.Xaml.Controls.ListView", LogLevel.Debug },
                // { "Windows.UI.Xaml.Controls.GridView", LogLevel.Debug },
                // { "Windows.UI.Xaml.Controls.VirtualizingPanelLayout", LogLevel.Debug },
                // { "Windows.UI.Xaml.Controls.NativeListViewBase", LogLevel.Debug },
                // { "Windows.UI.Xaml.Controls.ListViewBaseSource", LogLevel.Debug }, //iOS
                // { "Windows.UI.Xaml.Controls.ListViewBaseInternalContainer", LogLevel.Debug }, //iOS
                // { "Windows.UI.Xaml.Controls.NativeListViewBaseAdapter", LogLevel.Debug }, //Android
                // { "Windows.UI.Xaml.Controls.BufferViewCache", LogLevel.Debug }, //Android
                // { "Windows.UI.Xaml.Controls.VirtualizingPanelGenerator", LogLevel.Debug }, //WASM
            }
        )
        .AddConsole(LogLevel.Information);
}

Notice that the logging levels of various categories can be added and configured.

[!NOTE] Notice that console logging is configured by default- .AddConsole(LogLevel.Information);. This does not log output to the Visual Studio console when running a UWP app. The next task details how to add UWP logging.

Adding UWP logging

In order to support logging to the debug output view in Visual Studio, complete the following steps

To install the, IdentityModel NuGet package, right-click the solution, and select Manage NuGet packages for solution...
In the Manage Packages for Solution UI, select the Browse tab, search for Microsoft.Extensions.Logging.Debug and select it in the search results.

[!IMPORTANT] Only version 1.1.1 of the nuget package is supported by Uno at present.
On the right-side of the Manage Packages for Solution UI, ensure the UWP and WASM projects are selected, and then click Install.

In order to add UWP logging, configure AddDebug instead of (or in addition to) AddConsole. Review the code below for an example.

Configuring logging App.xaml.cs

/// <summary>
/// Configures global logging
/// </summary>
/// <param name="factory"></param>
static void ConfigureFilters(ILoggerFactory factory)
{
    factory
        .WithFilter(new FilterLoggerSettings
            {
                { "Uno", LogLevel.Warning },
                { "Windows", LogLevel.Warning },

                // Debug JS interop
                // { "Uno.Foundation.WebAssemblyRuntime", LogLevel.Debug },

                // Generic XAML events
                // { "Windows.UI.Xaml", LogLevel.Debug },
                // { "Windows.UI.Xaml.VisualStateGroup", LogLevel.Debug },
                // { "Windows.UI.Xaml.StateTriggerBase", LogLevel.Debug },
                // { "Windows.UI.Xaml.UIElement", LogLevel.Debug },

                // Layouter specific messages
                // { "Windows.UI.Xaml.Controls", LogLevel.Debug },
                // { "Windows.UI.Xaml.Controls.Layouter", LogLevel.Debug },
                // { "Windows.UI.Xaml.Controls.Panel", LogLevel.Debug },
                // { "Windows.Storage", LogLevel.Debug },

                // Binding related messages
                // { "Windows.UI.Xaml.Data", LogLevel.Debug },

                // DependencyObject memory references tracking
                // { "ReferenceHolder", LogLevel.Debug },

                // ListView-related messages
                // { "Windows.UI.Xaml.Controls.ListViewBase", LogLevel.Debug },
                // { "Windows.UI.Xaml.Controls.ListView", LogLevel.Debug },
                // { "Windows.UI.Xaml.Controls.GridView", LogLevel.Debug },
                // { "Windows.UI.Xaml.Controls.VirtualizingPanelLayout", LogLevel.Debug },
                // { "Windows.UI.Xaml.Controls.NativeListViewBase", LogLevel.Debug },
                // { "Windows.UI.Xaml.Controls.ListViewBaseSource", LogLevel.Debug }, //iOS
                // { "Windows.UI.Xaml.Controls.ListViewBaseInternalContainer", LogLevel.Debug }, //iOS
                // { "Windows.UI.Xaml.Controls.NativeListViewBaseAdapter", LogLevel.Debug }, //Android
                // { "Windows.UI.Xaml.Controls.BufferViewCache", LogLevel.Debug }, //Android
                // { "Windows.UI.Xaml.Controls.VirtualizingPanelGenerator", LogLevel.Debug }, //WASM
            }
        )
        //.AddConsole(LogLevel.Information);
#if DEBUG
        .AddConsole(LogLevel.Debug)
        .AddDebug(LogLevel.Debug);

#else
        .AddConsole(LogLevel.Information);
#endif
}

Notice the use of the pre-compiler directives to change the logging level when debugging.

Uno logging extensions

The Uno platform also provides an extension that simplifies the use of logging by making it simple to retrieve a reference to the logger.

In order to add logging to a class, add the following using statements namespaces:
```
using Microsoft.Extensions.Logging;
using Uno.Extensions;
```
In order to write output to a log, the Log extension method is available on an object instance, which then exposes the operations available from Microsoft.Extensions.Logging.LoggerExtensions. Here is an example on how to write error and information level messages:
```
if (discoveryClient.IsError)
{
    this.Log().LogError(discoveryClient.Error);
    throw new Exception(discoveryClient.Error);
}
this.Log().LogInformation($"UserInfoEndpoint: {discoveryClient.UserInfoEndpoint}");
```
[!TIP] To learn more about the logging capabilities, review the Microsoft logging reference materials here:
- Logging in .NET

Log output for not implemented member usage

By default, when a member is invoked at runtime that's not implemented by Uno (ie, marked with the [NotImplemented] attribute), an error message is logged.

Important

This feature flag must be set before the base.InitializeComponent() call within the App.xaml.cs constructor.

The logging behavior can be configured using feature flags:

By default, a message is only logged on the first usage of a given member. To log every time the member is invoked:
```
Uno.UI.FeatureConfiguration.ApiInformation.AlwaysLogNotImplementedMessages = true;
```
By default the message is logged as an error. To change the logging level:
```
Uno.UI.FeatureConfiguration.ApiInformation.NotImplementedLogLevel = LogLevel.Debug; // Raise not implemented usages as Debug messages
```
This can be used to suppress the not implemented output, if it's not useful.

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