AsyncRelayCommand Class

Definition

A command that mirrors the functionality of RelayCommand, with the addition of accepting a Func<TResult> returning a Task as the execute action, and providing an ExecutionTask property that notifies changes when ExecuteAsync(Object) is invoked and when the returned Task completes.

public sealed class AsyncRelayCommand : Microsoft.Toolkit.Mvvm.ComponentModel.ObservableObject, Microsoft.Toolkit.Mvvm.Input.IAsyncRelayCommand, System.ComponentModel.INotifyPropertyChanged, System.Windows.Input.ICommand
type AsyncRelayCommand = class
    inherit ObservableObject
    interface IAsyncRelayCommand
    interface IRelayCommand
    interface ICommand
    interface INotifyPropertyChanged
Public NotInheritable Class AsyncRelayCommand
Inherits ObservableObject
Implements IAsyncRelayCommand, ICommand, INotifyPropertyChanged
Inheritance
AsyncRelayCommand
Implements

Constructors

AsyncRelayCommand(Func<CancellationToken,Task>)

Initializes a new instance of the AsyncRelayCommand class that can always execute.

AsyncRelayCommand(Func<CancellationToken,Task>, Func<Boolean>)

Initializes a new instance of the AsyncRelayCommand class.

AsyncRelayCommand(Func<Task>)

Initializes a new instance of the AsyncRelayCommand class that can always execute.

AsyncRelayCommand(Func<Task>, Func<Boolean>)

Initializes a new instance of the AsyncRelayCommand class.

Properties

CanBeCanceled

Gets a value indicating whether running operations for this command can be canceled.

ExecutionTask

Gets the last scheduled Task, if available. This property notifies a change when the Task completes.

IsCancellationRequested

Gets a value indicating whether a cancelation request has been issued for the current operation.

IsRunning

Gets a value indicating whether the command currently has a pending operation being executed.

Methods

Cancel()

Communicates a request for cancelation.

CanExecute(Object)
Execute(Object)
ExecuteAsync(Object)

Provides a more specific version of Execute(Object), also returning the Task representing the async operation being executed.

NotifyCanExecuteChanged()

Notifies that the CanExecute(Object) property has changed.

OnPropertyChanged(PropertyChangedEventArgs)

Raises the PropertyChanged event.

(Inherited from ObservableObject)
OnPropertyChanged(String)

Raises the PropertyChanged event.

(Inherited from ObservableObject)
OnPropertyChanging(PropertyChangingEventArgs)

Raises the PropertyChanging event.

(Inherited from ObservableObject)
OnPropertyChanging(String)

Raises the PropertyChanging event.

(Inherited from ObservableObject)
SetProperty<T>(T, T, Action<T>, String)

Compares the current and new values for a given property. If the value has changed, raises the PropertyChanging event, updates the property with the new value, then raises the PropertyChanged event. This overload is much less efficient than SetProperty<T>(T, T, String) and it should only be used when the former is not viable (eg. when the target property being updated does not directly expose a backing field that can be passed by reference). For performance reasons, it is recommended to use a stateful callback if possible through the SetProperty<TModel,T>(T, T, TModel, Action<TModel,T>, String) whenever possible instead of this overload, as that will allow the C# compiler to cache the input callback and reduce the memory allocations. More info on that overload are available in the related XML docs. This overload is here for completeness and in cases where that is not applicable.

(Inherited from ObservableObject)
SetProperty<T>(T, T, IEqualityComparer<T>, Action<T>, String)

Compares the current and new values for a given property. If the value has changed, raises the PropertyChanging event, updates the property with the new value, then raises the PropertyChanged event. See additional notes about this overload in SetProperty<T>(T, T, Action<T>, String).

(Inherited from ObservableObject)
SetProperty<T>(T, T, IEqualityComparer<T>, String)

Compares the current and new values for a given property. If the value has changed, raises the PropertyChanging event, updates the property with the new value, then raises the PropertyChanged event. See additional notes about this overload in SetProperty<T>(T, T, String).

(Inherited from ObservableObject)
SetProperty<T>(T, T, String)

Compares the current and new values for a given property. If the value has changed, raises the PropertyChanging event, updates the property with the new value, then raises the PropertyChanged event.

(Inherited from ObservableObject)
SetProperty<TModel,T>(T, T, IEqualityComparer<T>, TModel, Action<TModel,T>, String)

Compares the current and new values for a given nested property. If the value has changed, raises the PropertyChanging event, updates the property and then raises the PropertyChanged event. The behavior mirrors that of SetProperty<T>(T, T, String), with the difference being that this method is used to relay properties from a wrapped model in the current instance. See additional notes about this overload in SetProperty<TModel,T>(T, T, TModel, Action<TModel,T>, String).

(Inherited from ObservableObject)
SetProperty<TModel,T>(T, T, TModel, Action<TModel,T>, String)

Compares the current and new values for a given nested property. If the value has changed, raises the PropertyChanging event, updates the property and then raises the PropertyChanged event. The behavior mirrors that of SetProperty<T>(T, T, String), with the difference being that this method is used to relay properties from a wrapped model in the current instance. This type is useful when creating wrapping, bindable objects that operate over models that lack support for notification (eg. for CRUD operations). Suppose we have this model (eg. for a database row in a table):

public class Person
{
    public string Name { get; set; }
}

We can then use a property to wrap instances of this type into our observable model (which supports notifications), injecting the notification to the properties of that model, like so:

public class BindablePerson : ObservableObject
{
    public Model { get; }

    public BindablePerson(Person model)
    {
        Model = model;
    }

    public string Name
    {
        get => Model.Name;
        set => Set(Model.Name, value, Model, (model, name) => model.Name = name);
    }
}

This way we can then use the wrapping object in our application, and all those "proxy" properties will also raise notifications when changed. Note that this method is not meant to be a replacement for SetProperty<T>(T, T, String), and it should only be used when relaying properties to a model that doesn't support notifications, and only if you can't implement notifications to that model directly (eg. by having it inherit from ObservableObject). The syntax relies on passing the target model and a stateless callback to allow the C# compiler to cache the function, which results in much better performance and no memory usage.

(Inherited from ObservableObject)
SetPropertyAndNotifyOnCompletion(ObservableObject+TaskNotifier, Task, Action<Task>, String)

Compares the current and new values for a given field (which should be the backing field for a property). If the value has changed, raises the PropertyChanging event, updates the field and then raises the PropertyChanged event. This method is just like SetPropertyAndNotifyOnCompletion(ObservableObject+TaskNotifier, Task, String), with the difference being an extra Action<T> parameter with a callback being invoked either immediately, if the new task has already completed or is null, or upon completion.

(Inherited from ObservableObject)
SetPropertyAndNotifyOnCompletion(ObservableObject+TaskNotifier, Task, String)

Compares the current and new values for a given field (which should be the backing field for a property). If the value has changed, raises the PropertyChanging event, updates the field and then raises the PropertyChanged event. The behavior mirrors that of SetProperty<T>(T, T, String), with the difference being that this method will also monitor the new value of the property (a generic Task) and will also raise the PropertyChanged again for the target property when it completes. This can be used to update bindings observing that Task or any of its properties. This method and its overload specifically rely on the ObservableObject.TaskNotifier type, which needs to be used in the backing field for the target Task property. The field doesn't need to be initialized, as this method will take care of doing that automatically. The ObservableObject.TaskNotifier type also includes an implicit operator, so it can be assigned to any Task instance directly. Here is a sample property declaration using this method:

private TaskNotifier myTask;

public Task MyTask
{
    get => myTask;
    private set => SetAndNotifyOnCompletion(ref myTask, value);
}
(Inherited from ObservableObject)
SetPropertyAndNotifyOnCompletion<T>(ObservableObject.TaskNotifier, Task<T>, Action<Task<T>>, String)

Compares the current and new values for a given field (which should be the backing field for a property). If the value has changed, raises the PropertyChanging event, updates the field and then raises the PropertyChanged event. This method is just like SetPropertyAndNotifyOnCompletion<T>(ObservableObject.TaskNotifier, Task<T>, String), with the difference being an extra Action<T> parameter with a callback being invoked either immediately, if the new task has already completed or is null, or upon completion.

(Inherited from ObservableObject)
SetPropertyAndNotifyOnCompletion<T>(ObservableObject.TaskNotifier, Task<T>, String)

Compares the current and new values for a given field (which should be the backing field for a property). If the value has changed, raises the PropertyChanging event, updates the field and then raises the PropertyChanged event. The behavior mirrors that of SetProperty<T>(T, T, String), with the difference being that this method will also monitor the new value of the property (a generic Task) and will also raise the PropertyChanged again for the target property when it completes. This can be used to update bindings observing that Task or any of its properties. This method and its overload specifically rely on the ObservableObject.TaskNotifier<T> type, which needs to be used in the backing field for the target Task property. The field doesn't need to be initialized, as this method will take care of doing that automatically. The ObservableObject.TaskNotifier<T> type also includes an implicit operator, so it can be assigned to any Task instance directly. Here is a sample property declaration using this method:

private TaskNotifier<int> myTask;

public Task<int> MyTask
{
    get => myTask;
    private set => SetAndNotifyOnCompletion(ref myTask, value);
}
(Inherited from ObservableObject)

Events

CanExecuteChanged
PropertyChanged (Inherited from ObservableObject)
PropertyChanging (Inherited from ObservableObject)

Applies to