.NET-Community-Toolkit/Microsoft.Toolkit.Mvvm/Input/RelayCommand{T}.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

#pragma warning disable SA1512

// This file is inspired from the MvvmLight library (lbugnion/MvvmLight),
// more info in ThirdPartyNotices.txt in the root of the project.

using System;
using System.Runtime.CompilerServices;

namespace Microsoft.Toolkit.Mvvm.Input
{
    /// <summary>
    /// A generic command whose sole purpose is to relay its functionality to other
    /// objects by invoking delegates. The default return value for the CanExecute
    /// method is <see langword="true"/>. This class allows you to accept command parameters
    /// in the <see cref="Execute(T)"/> and <see cref="CanExecute(T)"/> callback methods.
    /// </summary>
    /// <typeparam name="T">The type of parameter being passed as input to the callbacks.</typeparam>
    public sealed class RelayCommand<T> : IRelayCommand<T>
    {
        /// <summary>
        /// The <see cref="Action"/> to invoke when <see cref="Execute(T)"/> is used.
        /// </summary>
        private readonly Action<T> execute;

        /// <summary>
        /// The optional action to invoke when <see cref="CanExecute(T)"/> is used.
        /// </summary>
        private readonly Func<T, bool>? canExecute;

        /// <inheritdoc/>
        public event EventHandler? CanExecuteChanged;

        /// <summary>
        /// Initializes a new instance of the <see cref="RelayCommand{T}"/> class that can always execute.
        /// </summary>
        /// <param name="execute">The execution logic.</param>
        /// <remarks>
        /// Due to the fact that the <see cref="System.Windows.Input.ICommand"/> interface exposes methods that accept a
        /// nullable <see cref="object"/> parameter, it is recommended that if <typeparamref name="T"/> is a reference type,
        /// you should always declare it as nullable, and to always perform checks within <paramref name="execute"/>.
        /// </remarks>
        public RelayCommand(Action<T> execute)
        {
            this.execute = execute;
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="RelayCommand{T}"/> class.
        /// </summary>
        /// <param name="execute">The execution logic.</param>
        /// <param name="canExecute">The execution status logic.</param>
        /// <remarks>See notes in <see cref="RelayCommand{T}(Action{T})"/>.</remarks>
        public RelayCommand(Action<T> execute, Func<T, bool> canExecute)
        {
            this.execute = execute;
            this.canExecute = canExecute;
        }

        /// <inheritdoc/>
        public void NotifyCanExecuteChanged()
        {
            CanExecuteChanged?.Invoke(this, EventArgs.Empty);
        }

        /// <inheritdoc/>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public bool CanExecute(T parameter)
        {
            return this.canExecute?.Invoke(parameter) != false;
        }

        /// <inheritdoc/>
        public bool CanExecute(object? parameter)
        {
            if (typeof(T).IsValueType &&
                parameter is null &&
                this.canExecute is null)
            {
                return true;
            }

            return CanExecute((T)parameter!);
        }

        /// <inheritdoc/>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void Execute(T parameter)
        {
            if (CanExecute(parameter))
            {
                this.execute(parameter);
            }
        }

        /// <inheritdoc/>
        public void Execute(object? parameter)
        {
            Execute((T)parameter!);
        }
    }
}