Options

Microsoft has introduced the options pattern that is used to configure a group of settings used by the framework services. This pattern is implemented by the Microsoft.Extensions.Options NuGet package, so it is usable by any type of applications in addition to ASP.NET Core based applications.

ABP framework follows this option pattern and defines options classes to configure the framework and the modules (they are explained in the documents of the related feature).

Since the Microsoft documentation explains the pattern in detail, no reason to repeat all. However, ABP adds a few more features and they will be explained here.

Configure Options

You typically configure options in the ConfigureServices of the Startup class. However, since ABP framework provides a modular infrastructure, you configure options in the ConfigureServices of your module. Example:

public override void ConfigureServices(ServiceConfigurationContext context)
{
    context.Services.Configure<AbpAuditingOptions>(options =>
    {
        options.IsEnabled = false;
    });
}

• AbpAuditingOptions is a simple class defines some properties like IsEnabled used here.
• AbpModule base class defines Configure method to make the code simpler. So, instead of context.Services.Configure<...>, you can directly use the Configure<...> shortcut method.

If you are developing a reusable module, you may need to define an options class to allow developers to configure your module. In this case, define a plain options class as shown below:

public class MyOptions
{
    public int Value1 { get; set; }
    public bool Value2 { get; set; }
}

Then developers can configure your options just like the AbpAuditingOptions example above:

public override void ConfigureServices(ServiceConfigurationContext context)
{
    Configure<MyOptions>(options =>
    {
        options.Value1 = 42;
        options.Value2 = true;
    });
}

• In this example, used the shortcut Configure<...> method.

Get the Option Value

Whenever you need to get the value of an option, inject the IOptions<TOption> service into your class and use its .Value property. Example:

public class MyService : ITransientDependency
{
    private readonly MyOptions _options;
    public MyService(IOptions<MyOptions> options)
    {
        _options = options.Value; //Notice the options.Value usage!
    }
    public void DoIt()
    {
        var v1 = _options.Value1;
        var v2 = _options.Value2;
    }
}

Read the Microsoft documentation for all details of the options pattern.

Pre Configure

One restriction of the options pattern is that you can only resolve (inject) the IOptions<MyOptions> and get the option values when the dependency injection configuration completes (that means the ConfigureServices methods of all modules complete).

If you are developing a module, you may need to allow developers to set some options and use these options in the dependency injection registration phase. You may need to configure other services or change the dependency injection registration code based on these option values.

For such cases, ABP introduces the PreConfigure<TOptions> and the ExecutePreConfiguredActions<TOptions> extension methods for the IServiceCollection. The pattern works as explained below.

Define a pre option class in your module. Example:

public class MyPreOptions
{
    public bool MyValue { get; set; }
}

Then any module class depends on your module can use the PreConfigure<TOptions> method in its PreConfigureServices method. Example:

public override void PreConfigureServices(ServiceConfigurationContext context)
{
    PreConfigure<MyPreOptions>(options =>
    {
        options.MyValue = true;
    });
}

Multiple modules can pre-configure the options and override the option values based on their dependency order.

Finally, your module can execute the ExecutePreConfiguredActions method in its ConfigureServices method to get the configured option values. Example:

public override void ConfigureServices(ServiceConfigurationContext context)
{
    var options = context.Services.ExecutePreConfiguredActions<MyPreOptions>();
    if (options.MyValue)
    {
        //...
    }
}