Overview

Filters allow to intercept calls to these methods from the UI. They can be used to validate request, log or handle any errors, and more.

DotVVM can apply action or exception filters on individual methods, on specific viewmodel classes, or globally for all viewmodels in your application.

Please note that the filters are currently supported only in command binding, not in static commands.

Usage of filters

Because the base classes of the filters inherit from the Attribute class, you can apply those filters on a viewmodel or a method as an attribute.

[MyValidationFilter]
public class DemoViewModel 
{
	[MyCustomFilter]
	public void Command1() 
	{
	}

	public void Command2() 
	{
	}
}

In the example above, there is a MyValidationFilter applied on the viewmodel class, which means that every command referencing a method in the viewmodel will use this filter.

If you call the {command: Command1()} from a button in the page, MyValidationFilter and also the MyCustomFilter will be applied.

Like the Authorize attribute (which is also an action filter), the filter is executed if the command binding in the page references the method. If you call Command1() from the Command2() method and the binding in the page references the Command2 method, the MyCustomFilter will not be applied.

Register filter globally

If you need to apply a filter globally, navigate in the DotvvmStartup.cs class and register the filter in the config.Runtime.GlobalFilters collection in the DotvvmConfiguration object.

config.Runtime.GlobalFilters.Add(new ErrorHandlingActionFilter());

Combine filters

You can apply multiple filters on a viewmodel or a method. The filters are called (in the order they were registered in the GlobalFilters collection), or in the order of the attributes on the class or a method.

All the filter methods except the OnCommandExecutedAsync method are executed in the following order:

• Global filters (in the order they were registered)

• Filter applied on the viewmodel class (in the order they were registered)

• Filters applied on the individual methods (in the order they were registered)

The OnCommandExecutedAsync methods uses the reverse order of action filters.

See also

• Action filters
• Exception filters