How do I set up NLog targets and rules in an MvvmCross application

Step 1: Install NLog Packages

First, you need to install the necessary NLog packages in your project. This includes `NLog` and `NLog.Config`. You can install these via NuGet Package Manager.

For MvvmCross projects, ensure you install the packages in both the Android and iOS projects if applicable.

Step 2: Configure NLog

NLog can be configured using an XML file (`NLog.config`) or programmatically in C#. For most cases, using an XML configuration is simpler and more flexible.

XML Configuration

1. Create an NLog.config File: In your project, add a new XML file named `NLog.config`. This file will contain your logging configuration.

2. Define Targets: Targets specify where log messages will be written. Common targets include files, console, and databases.

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3. Define Rules: Rules determine which log messages are written to which targets based on log levels and logger names.

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Programmatic Configuration

If you prefer to configure NLog programmatically, you can do so in your application's startup code.

csharp
var config = new LoggingConfiguration();

var fileTarget = new FileTarget();
fileTarget.FileName = "${specialfolder:folder=MyDocuments}/logs/${shortdate}.log";
fileTarget.Layout = "${longdate}|${level:uppercase=true}|${logger}|${message}";
config.AddTarget("file", fileTarget);

var consoleTarget = new ColoredConsoleTarget();
consoleTarget.Layout = "${longdate}|${level:uppercase=true}|${logger}|${message}";
config.AddTarget("console", consoleTarget);

var rule1 = new LoggingRule("*", LogLevel.Debug, "file");
var rule2 = new LoggingRule("*", LogLevel.Debug, "console");
config.LoggingRules.Add(rule1);
config.LoggingRules.Add(rule2);

LogManager.Configuration = config;

Step 3: Integrate with MvvmCross

To use NLog as the log provider in MvvmCross, you need to override the `GetDefaultLogProviderType` method in your `Setup.cs` file.

csharp
public override MvxLogProviderType GetDefaultLogProviderType() => MvxLogProviderType.NLog;

Ensure that your `NLog.config` file is set as an Embedded Resource in your project properties.

Step 4: Logging in Your Application

Once NLog is configured, you can use it to log messages in your application. Here's how you might log a debug message:

csharp
private static readonly IMvxLog _logger = Mvx.IoCProvider.Resolve().GetLogFor();

_logger.Debug("This is a debug message.");

This setup will allow you to log messages to both a file and the console, with the log level set to Debug or higher.

Additional Tips

- Custom Layouts: You can customize the layout of your log messages using various layout renderers like `${longdate}`, `${level}`, `${logger}`, and `${message}`[1].
- Multiple Targets: You can log to multiple targets simultaneously by specifying multiple targets in your rules[9].
- Error Handling: Ensure that NLog is configured to handle exceptions properly by setting `throwExceptions="false"` in your `NLog.config` file[4].