Logging to device (Android.Util.Log/CoreFoundation.OSLog)

[MartinRobins]

Unless it already exists (in which case I cannot find it), it would be useful to add ILogging providers for Android.Util.Log and CoreFoundation.OSLog so that anything written to the ILogger<> can be picked up in the device logs.

[LeoJHarris]

if you are trying to log to Device Log you can do the following

Android

public class AndroidLoggerProvider : ILoggerProvider
{
    ILogger ILoggerProvider.CreateLogger(string categoryName)
    {
        // Category name is often the full class name, like MyApp.ViewModel.MyViewModel This removes
        // the namespace:
        int lastDotPos = categoryName.LastIndexOf('.');
        if (lastDotPos > 0)
        {
            categoryName = categoryName[(lastDotPos + 1)..];
        }

        return new AndroidLogger(categoryName);
    }

    void IDisposable.Dispose() => GC.SuppressFinalize(this);
}

public class AndroidLogger(string category) : ILogger
{
    IDisposable ILogger.BeginScope<TState>(TState state) => null!;

    bool ILogger.IsEnabled(LogLevel logLevel) => true;

    void ILogger.Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception? exception, Func<TState, Exception?, string> formatter)
    {
        string message = formatter(state, exception);

        Java.Lang.Throwable? throwable = null;

        if (exception is not null)
        {
            throwable = Java.Lang.Throwable.FromException(exception);
        }

        switch (logLevel)
        {
            case LogLevel.Trace:
                Android.Util.Log.Verbose(category, throwable, message);
                break;

            case LogLevel.Debug:
                Android.Util.Log.Debug(category, throwable, message);
                break;

            case LogLevel.Information:
                Android.Util.Log.Info(category, throwable, message);
                break;

            case LogLevel.Warning:
                Android.Util.Log.Warn(category, throwable, message);
                break;

            case LogLevel.Error:
                Android.Util.Log.Error(category, throwable, message);
                break;

            case LogLevel.Critical:
                Android.Util.Log.Wtf(category, throwable, message);
                break;
        }
    }
}

iOS

public class iOSLoggerProvider : ILoggerProvider
{
    public ILogger CreateLogger(string categoryName)
    {
        // Category name is often the full class name, like MyApp.ViewModel.MyViewModel This removes
        // the namespace:
        int lastDotPos = categoryName.LastIndexOf('.');
        if (lastDotPos > 0)
        {
            categoryName = categoryName[(lastDotPos + 1)..];
        }

        return new iOSLogger(categoryName);
    }

    public void Dispose() => GC.SuppressFinalize(this);
}

public class iOSLogger : ILogger
{
    public iOSLogger(string category)
    {
        _category = category;
    }

    private readonly string _category;

    public IDisposable BeginScope<TState>(TState state) => null!;

    public bool IsEnabled(LogLevel logLevel) => true;

    public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception? exception, Func<TState, Exception?, string> formatter)
    {
        string message = formatter(state, exception);

        switch (logLevel)
        {
            case LogLevel.Trace:
            case LogLevel.Debug:
                CoreFoundation.OSLog.Default.Log(OSLogLevel.Debug, $"{_category}: {message}");
                break;

            case LogLevel.Information:
                CoreFoundation.OSLog.Default.Log(OSLogLevel.Info, $"{_category}: {message}");
                break;

            case LogLevel.Warning:
                CoreFoundation.OSLog.Default.Log(OSLogLevel.Default, $"{_category}: {message}");
                break;

            case LogLevel.Error:
                CoreFoundation.OSLog.Default.Log(OSLogLevel.Error, $"{_category}: {message}");
                break;

            case LogLevel.Critical:
                CoreFoundation.OSLog.Default.Log(OSLogLevel.Fault, $"{_category}: {message}");
                break;
        }
    }
}

Usage

ILoggerProvider loggerProvider = ServiceProvider.GetRequiredService<ILoggerProvider>(); // Or constructor injection

ILogger logger = loggerProvider.CreateLogger(nameof(System.Diagnostics.Activity));

logger?.LogError("Message to Log");