How to enable WPF slide animation more physically?

Question

If we want to shift the screen, we need some events.

How Mouse Move Event, Mouse Down Event, Mouse UP event But the problem is , we can only do the animation, but when the finger touches the screen , I mean, when he touches the screen movement, it will move when we will release it to stop (or give this position allows him to stay there). But I want the animation to look like the iPhone’s main screen. If our finger weakens faster, the animation becomes faster (or the animation slides to a farther place).

Just like now, we use Photoshop, when the image approaches a very large one, when we move our hand faster, it will move very far.

Another example is that it will slow down very slowly, and not immediately. He will also know that my finger is sliding quickly or slowly ... then it will slide slowly or quickly ...

Answer 1

. , , . () , (OnPreviewMouseDown, OnPreviewMouseUp OnPreviewMouseMove). OnPreviewMouseMove , . , , "".

Answer 2

, , ScrollViewer.
, .

public partial class HomeFeed : BaseControl
{
    public HomeFeed()
    {
        InitializeComponent();
    }

    private bool IsDragging
    {
        get { return _isDragging; }
        set
        {
            var start = _isDragging && !value;
            _isDragging = value;

            if (start)
            {
                new Thread(x =>
                {
                    var c = 0;
                    while (ApplyVelocity())
                    {
                        c++;
                        Thread.Sleep(15);
                    }

                }).Start();
            }
        }
    }

    private Point _mousePosition;
    private Velocity _velocity = new Velocity();
    private bool _isDragging;

    private void HomeScrollViewer_OnMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        IsDragging = true;
        _velocity.Reset();
        _mousePosition = e.GetPosition(this);
        e.Handled = true;
    }

    private void HomeScrollViewer_OnPreviewMouseMove(object sender, MouseEventArgs e)
    {
        if (!IsDragging) return;

        var pos = e.GetPosition(this);
        var y = pos.Y - _mousePosition.Y;

        if (y == 0)
        {
            return;
        }

        _velocity.TryUpdate(y);

        HomeScrollViewer.ScrollToVerticalOffset(HomeScrollViewer.VerticalOffset - y);
        _mousePosition = pos;
    }

    private void HomeScrollViewer_OnMouseLeftButtonUp(object sender, MouseButtonEventArgs e)
    {
        if (!IsDragging) return;

        IsDragging = false;
        e.Handled = true;
    }

    private void HomeScrollViewer_OnMouseLeave(object sender, MouseEventArgs e)
    {
        if (!IsDragging) return;

        IsDragging = false;
        e.Handled = true;
    }

    private bool ApplyVelocity()
    {
        if (IsDragging || _velocity.Value == 0)
        {
            return false;
        }

        Dispatcher.BeginInvoke(new Action(() => HomeScrollViewer.ScrollToVerticalOffset(HomeScrollViewer.VerticalOffset - _velocity.Value)));

        var size = Math.Abs(_velocity.Value);
        var sign = size / _velocity.Value;

        _velocity.Value = sign * Math.Max(0, Math.Min(size*0.95, size - 1));
        return true;
    }
}

public class Velocity
{
    private readonly int _timespan;
    public double Value { get; set; }
    public DateTime SetAt { get; set; }

    public Velocity(int timespan = 1000)
    {
        _timespan = timespan;
        Value = 0;
        SetAt = DateTime.Now;
    }

    public void TryUpdate(double value)
    {
        if (value == 0)
        {
            return;
        }

        if (SetAt.Add(TimeSpan.FromMilliseconds(_timespan)) > DateTime.Now)
        {
            SetAt = DateTime.Now;
            Value = value;
            return;
        }

        if (value*Value < 0)
        {
            SetAt = DateTime.Now;
            Value = value;
            return;
        }

        if (Math.Abs(value) > Math.Abs(Value))
        {
            SetAt = DateTime.Now;
            Value = value;
            return;
        }
    }

    public void Reset()
    {
        Value = 0;
        SetAt = DateTime.Now;
    }
}