PanGestureRecognizer 在拖动过程中偶尔出现

Question

我正在使用 PanGestureRecognizer 为图像创建一个简单的拖动动画。但是，当拖动正在进行时，TotalX 和 TotalY 值不一致，它们似乎在我拖动时在 2 个值之间跳跃/闪烁/颤动。以下是值的原始跟踪示例：

[0:] PanUpdated: StatusType: Started, GestureId: 0, TotalX: 0, TotalY: 0
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 11.1617584228516, TotalY: 11.9234619140625
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 2.45475260416667, TotalY: 2.80341593424479
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 11.8422292073568, TotalY: 12.5428161621094
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 3.20952860514323, TotalY: 3.77924601236979
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 12.6615346272786, TotalY: 13.5227355957031
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 4.03237915039063, TotalY: 4.76089477539063
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 12.8976643880208, TotalY: 14.1595052083333
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 4.93493143717448, TotalY: 5.72846476236979
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 13.551747639974, TotalY: 14.7833862304688
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 5.67492167154948, TotalY: 6.68665568033854
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 14.1307627360026, TotalY: 15.5877075195313
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 6.67552185058594, TotalY: 7.82212320963542
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 14.8915608723958, TotalY: 16.3966369628906
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 7.67821248372396, TotalY: 8.44764200846354
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 15.2916819254557, TotalY: 16.9883219401042
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 8.57093811035156, TotalY: 9.37423706054688
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 15.8519948323568, TotalY: 17.2493794759115
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 9.13496907552083, TotalY: 10.1264038085938
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 16.5894927978516, TotalY: 17.6655578613281
[0:] PanUpdated: StatusType: Running, GestureId: 0, TotalX: 10.049072265625, TotalY: 11.0558268229167
[0:] PanUpdated: StatusType: Completed, GestureId: 0, TotalX: 0, TotalY: 0

但是，如果我将手势添加到容器中，值就会正常流动。

这是我的页面：

<ContentPage>
    <AbsoluteLayout >
        <Image x:Name="Card" Source="CardBack_Red.png" />
    </AbsoluteLayout>
</ContentPage>

以及后面的代码：

    public partial class MainPage : ContentPage
    {
        double x, y;

        public MainPage()
        {
            InitializeComponent();

            var panGesture = new PanGestureRecognizer();
            panGesture.PanUpdated += PanGesture_PanUpdated;
            panGesture.TouchPoints = 1;
            Card.GestureRecognizers.Add(panGesture);
        }

        private void PanGesture_PanUpdated(object sender, PanUpdatedEventArgs e)
        {
            Debug.WriteLine($"PanUpdated: StatusType: {e.StatusType}, GestureId: {e.GestureId}, TotalX: {e.TotalX}, TotalY: {e.TotalY}");

            Image card = (Image)sender;

            switch (e.StatusType)
            {
                case GestureStatus.Started:
                    x = card.TranslationX;
                    y = card.TranslationY;
                    break;
                case GestureStatus.Running:
                    card.TranslationX = x + e.TotalX;
                    card.TranslationY = y + e.TotalY;
                    break;
            }
        }
    }
}

好像我在打架，但我不知道是什么，有什么想法吗？

谢谢

-约翰

Answer 1

已解决

原来我的平移算法有误，GestureStatus.Running 的情况需要将增量直接添加到图像平移坐标，而不是同时添加起始平移。我上面的代码中的情况看起来像这样：

        case GestureStatus.Running:
            dragCard.TranslationX += e.TotalX;
            dragCard.TranslationY += e.TotalY;
            break;

我找到了更好的 sample here，帮助很大。

PanGestureRecognizer 在拖动过程中偶尔出现

PanGestureRecognizer sporadic during drag

xamarin.forms

android-animation

uigesturerecognizer

uipangesturerecognizer