Clearer – A Gesture-Driven Windows 8 To-Do Application

using ClearStyle.ViewModel;
using LinqToVisualTree;
using System;
using System.Linq;
using Windows.UI;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Media.Animation;

namespace ClearStyle.Interactions
{
  /// <summary>
  /// Adds an interaction that allows the user to swipe an item to mark it as complete
  /// or delete it
  /// </summary>
  public class SwipeInteraction : InteractionBase, IInteraction
  {

    public SwipeInteraction()
    {
    }

    public override void AddElement(FrameworkElement manipulationElement, FrameworkElement transformElement)
    {
      manipulationElement.ManipulationDelta += Element_ManipulationDelta;
      manipulationElement.ManipulationCompleted += Element_ManipulationCompleted;
      manipulationElement.ManipulationStarted += Element_ManipulationStarted;
      manipulationElement.Tag = transformElement;
    }

    private void Element_ManipulationStarted(object sender, ManipulationStartedRoutedEventArgs e)
    {
      if (!IsEnabled)
        return;

      if (Math.Abs(e.Cumulative.Translation.Y) < Math.Abs(e.Cumulative.Translation.X))
      {
        IsActive = true;

        // initialize the drag
        FrameworkElement transformElement = ((FrameworkElement)sender).Tag as FrameworkElement;
        transformElement.SetHorizontalOffset(0);
      }
    }

    private void Element_ManipulationCompleted(object sender, ManipulationCompletedRoutedEventArgs e)
    {
      if (!IsActive)
        return;

      FrameworkElement transformElement = ((FrameworkElement)sender).Tag as FrameworkElement;

      if (Math.Abs(e.Cumulative.Translation.X) > transformElement.ActualWidth / 3) 
      {
        if (e.Cumulative.Translation.X < 0.0)
        {
          ToDoItemDeletedAction(transformElement);
        }
        else
        {
          ToDoItemCompletedAction(transformElement);
        }
      }
      else
      {
        ToDoItemBounceBack(transformElement);
      }

      IsActive = false;
    }

    private void Element_ManipulationDelta(object sender, ManipulationDeltaRoutedEventArgs e)
    {
      if (!IsEnabled || !IsActive)
        return;

      FrameworkElement transformElement = ((FrameworkElement)sender).Tag as FrameworkElement;

      // handle the drag to offset the element
      double offset = transformElement.GetHorizontalOffset().Value + e.Delta.Translation.X;
      transformElement.SetHorizontalOffset(offset);
    }


    private double TickAndCrossOpacity(double offset)
    {
      offset = Math.Abs(offset);
      if (offset < 50)
        return 0;

      offset -= 50;
      double opacity = offset / 100;

      opacity = Math.Max(Math.Min(opacity, 1), 0);
      return opacity;
    }

    private void ToDoItemBounceBack(FrameworkElement fe)
    {
      var trans = fe.GetHorizontalOffset().Transform;

      trans.Animate(trans.X, 0, "X", 300, 0, new BounceEase()
      {
        Bounciness = 5,
        Bounces = 2
      });
    }

    private void ToDoItemDeletedAction(FrameworkElement deletedElement)
    {
      // find the model object that was deleted
      ToDoItem deletedItem = deletedElement.DataContext as ToDoItem;
      _todoItems.Remove(deletedItem);
    }

    private void ToDoItemCompletedAction(FrameworkElement fe)
    {
      // set the mode object to complete
      ToDoItem completedItem = fe.DataContext as ToDoItem;
      completedItem.Completed = true;
      completedItem.Color = Colors.Green;

      // bounce back into place
      ToDoItemBounceBack(fe);
    }
  }
}