.NET Core development actual combat (Lesson 12: monitor configuration changes) - Study Notes

12 | monitor configuration changes: hot update the core configuration capabilities

This section explains how to use code to monitor configuration changes and make some moves

When we need to track configuration changes occur, you can perform certain operations when changes occur

The main configuration provides a GetReloadToken method, which is a key method for tracking configuration

Then use the code on a

var builder = new ConfigurationBuilder();
builder.AddJsonFile("appsettings.json", optional:true, reloadOnChange:true);
var configurationRoot = builder.Build();

IChangeToken token = configurationRoot.GetReloadToken();

IChangeToken has two properties and a method

public interface IChangeToken
{
    bool HasChanged { get; }
    
    bool ActiveChangeCallbacks { get; }
    
    IDisposable RegisterChangeCallback(Action<object> callback, object state);
}

Then Callback Registration

token.RegisterChangeCallback(state =>
{
    Console.WriteLine($"Key1:{configurationRoot["Key1"]}");
    Console.WriteLine($"Key2:{configurationRoot["Key2"]}");
    Console.WriteLine($"Key3:{configurationRoot["Key3"]}");
}, configurationRoot);

Start the program, modify the configuration file, triggering Callback

Repeatedly modify the configuration file has no effect?

After IChangeToken because this object can only be used once, that is to capture and execute the code change, we need to re-acquire a new IChangeToken, re-registration

token.RegisterChangeCallback(state =>
{
    Console.WriteLine($"Key1:{configurationRoot["Key1"]}");
    Console.WriteLine($"Key2:{configurationRoot["Key2"]}");
    Console.WriteLine($"Key3:{configurationRoot["Key3"]}");

    token = configurationRoot.GetReloadToken();
    token.RegisterChangeCallback(state2 =>
    {
        Console.WriteLine();
    }, configurationRoot);
}, configurationRoot);

This will turn into an infinite loop process, Microsoft actually provides a quick extension method is more convenient to use, this method can help us easily handle this matter, which means that after each trigger can complete rebind

ChangeToken.OnChange(() => configurationRoot.GetReloadToken(), () =>
{
    Console.WriteLine($"Key1:{configurationRoot["Key1"]}");
    Console.WriteLine($"Key2:{configurationRoot["Key2"]}");
    Console.WriteLine($"Key3:{configurationRoot["Key3"]}");
});

The first argument is a method of obtaining IChangeToken

The second parameter is a process of changing the implantation method

Start the program, modify the configuration file, multiple trigger Callback

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