ICommand ICommand ICommand ICommand Interface

Definition

Defines the command behavior of an interactive UI element that performs an action when invoked, such as sending an email, deleting an item, or submitting a form.

public : interface ICommand
struct winrt::Windows::UI::Xaml::Input::ICommand
public interface ICommand
Public Interface ICommand
Attributes

Windows 10 requirements

Device family
Windows 10 (introduced v10.0.10240.0)
API contract
Windows.Foundation.UniversalApiContract (introduced v1)

Examples

Here, we define a command that simply relays its functionality to other objects.

See the UI basics (XAML) sample for the complete application.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;
namespace AppUIBasics.Common
{
    /// <summary>
    /// A command whose sole purpose is to relay its functionality 
    /// to other objects by invoking delegates. 
    /// The default return value for the CanExecute method is 'true'.
    /// RaiseCanExecuteChanged needs to be called whenever
    /// CanExecute is expected to return a different value.
    /// </summary>
    public class RelayCommand : ICommand
    {
        private readonly Action _execute;
        private readonly Func<bool> _canExecute;
        /// <summary>
        /// Raised when RaiseCanExecuteChanged is called.
        /// </summary>
        public event EventHandler CanExecuteChanged;
        /// <summary>
        /// Creates a new command that can always execute.
        /// </summary>
        /// <param name="execute">The execution logic.</param>
        public RelayCommand(Action execute)
            : this(execute, null)
        {
        }
        /// <summary>
        /// Creates a new command.
        /// </summary>
        /// <param name="execute">The execution logic.</param>
        /// <param name="canExecute">The execution status logic.</param>
        public RelayCommand(Action execute, Func<bool> canExecute)
        {
            if (execute == null)
                throw new ArgumentNullException("execute");
            _execute = execute;
            _canExecute = canExecute;
        }
        /// <summary>
        /// Determines whether this RelayCommand can execute in its current state.
        /// </summary>
        /// <param name="parameter">
        /// Data used by the command. If the command does not require data to be passed, 
        /// this object can be set to null.
        /// </param>
        /// <returns>true if this command can be executed; otherwise, false.</returns>
        public bool CanExecute(object parameter)
        {
            return _canExecute == null ? true : _canExecute();
        }
        /// <summary>
        /// Executes the RelayCommand on the current command target.
        /// </summary>
        /// <param name="parameter">
        /// Data used by the command. If the command does not require data to be passed, 
        /// this object can be set to null.
        /// </param>
        public void Execute(object parameter)
        {
            _execute();
        }
        /// <summary>
        /// Method used to raise the CanExecuteChanged event
        /// to indicate that the return value of the CanExecute
        /// method has changed.
        /// </summary>
        public void RaiseCanExecuteChanged()
        {
            var handler = CanExecuteChanged;
            if (handler != null)
            {
                handler(this, EventArgs.Empty);
            }
        }
    }
}

Remarks

For a basic example, see the Button control, which invokes a command when a user clicks it. There are two ways you manage the command experience:

  • Handle the Click event
  • Bind the Command property to an ICommand implementation that describes the command logic

Methods

CanExecute(Object) CanExecute(Object) CanExecute(Object) CanExecute(Object)

Retrieves whether the command can execute in its current state.

Execute(Object) Execute(Object) Execute(Object) Execute(Object)

Defines the method to be called when the command is invoked.

Events

CanExecuteChanged CanExecuteChanged CanExecuteChanged CanExecuteChanged

Occurs whenever something happens that affects whether the command can execute.

See also