StartAnimationAction.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.

using Microsoft.Xaml.Interactivity;
using CommunityToolkit.WinUI.Animations;

namespace CommunityToolkit.WinUI.Behaviors;

/// <summary>
/// An <see cref="IAction"/> implementation that can trigger a target <see cref="AnimationSet"/> instance.
/// </summary>
public sealed partial class StartAnimationAction : DependencyObject, IAction
{
    /// <summary>
    /// Gets or sets the linked <see cref="AnimationSet"/> instance to invoke.
    /// </summary>
    public AnimationSet Animation
    {
        get => (AnimationSet)GetValue(AnimationProperty);
        set => SetValue(AnimationProperty, value);
    }

    /// <summary>
    /// Identifies the <seealso cref="Animation"/> dependency property.
    /// </summary>
    public static readonly DependencyProperty AnimationProperty = DependencyProperty.Register(
        nameof(Animation),
        typeof(AnimationSet),
        typeof(StartAnimationAction),
        new PropertyMetadata(null));

    /// <summary>
    /// Gets or sets the object to start the specified animation on. If not specified, will use the current object the parent animation is running on.
    /// </summary>
    public UIElement TargetObject
    {
        get => (UIElement)GetValue(TargetObjectProperty);
        set => SetValue(TargetObjectProperty, value);
    }

    /// <summary>
    /// Identifies the <seealso cref="TargetObject"/> dependency property.
    /// </summary>
    public static readonly DependencyProperty TargetObjectProperty = DependencyProperty.Register(
        nameof(TargetObject),
        typeof(UIElement),
        typeof(StartAnimationAction),
        new PropertyMetadata(null));

    /// <inheritdoc/>
    public object Execute(object sender, object parameter)
    {
        if (Animation is null)
        {
            ThrowArgumentNullException();
        }

        UIElement? parent = null;
        if (Animation is not null)
        {
            if (TargetObject is not null)
            {
                Animation.Start(TargetObject);
            }
            else if (Animation.ParentReference?.TryGetTarget(out parent) == true) //// TODO: Tidy... apply same pattern to Activities?
            {
                Animation.Start(parent!);
            }
            else
            {
                Animation.Start(sender as UIElement);
            }
        }
        return null!;

        static void ThrowArgumentNullException() => throw new ArgumentNullException(nameof(Animation));
    }
}