c# - 可拖动的Boxview崩溃错误Xamarin

问题在于可拖动视图，在代码local:draggableview的第一部分中，程序在代码的Xaml部分崩溃，但是我无法弄清楚问题出在哪里。我已经删除了draggableview，并尝试在代码的非xaml部分中设置断点，但是我无法找出引起问题的原因。

<ContentPage>
    <ContentPage.Padding>
        <OnPlatform x:TypeArguments="Thickness">
            <On Platform="iOS, Android" Value="0,40,0,0" />
        </OnPlatform>
    </ContentPage.Padding>
    <Grid BackgroundColor="White" ColumnSpacing="10" RowSpacing="10">
        <Label Text="Red" FontSize="Medium" HorizontalOptions="Center" />
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>

        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="*" />
        </Grid.ColumnDefinitions>

        <BoxView Color="Black" Grid.Column="1" Grid.RowSpan="1"/>
        <BoxView Color="Gray" Grid.Column="2" Grid.RowSpan="1"/>
        <Label Text="9" Font ="60" Grid.Row="1" HorizontalTextAlignment="Center" VerticalTextAlignment="Center" TextColor="Black" />
        <Label Text="8" Font ="60" Grid.Row="2" HorizontalTextAlignment="Center" VerticalTextAlignment="Center" TextColor="Black" />
        <Label Text="7" Font ="60" Grid.Row="3" HorizontalTextAlignment="Center" VerticalTextAlignment="Center" TextColor="Black" />
        <Label Text="6" Font ="60" Grid.Row="4" HorizontalTextAlignment="Center" VerticalTextAlignment="Center" TextColor="Black" />
        <Label Text="5" Font ="60" Grid.Row="5" HorizontalTextAlignment="Center" VerticalTextAlignment="Center" TextColor="Black" />
        <Label Text="4" Font ="60" Grid.Row="6" HorizontalTextAlignment="Center" VerticalTextAlignment="Center" TextColor="Black" />
        <Label Text="3" Font ="60" Grid.Row="7" HorizontalTextAlignment="Center" VerticalTextAlignment="Center" TextColor="Black" />
        <Label Text="2" Font ="60" Grid.Row="8" HorizontalTextAlignment="Center" VerticalTextAlignment="Center" TextColor="Black" />
        <Label Text="1" Font ="60" Grid.Row="9" HorizontalTextAlignment="Center" VerticalTextAlignment="Center" TextColor="Black" />
        <Label Text="0" Font ="60" Grid.Row="10" HorizontalTextAlignment="Center" VerticalTextAlignment="Center" TextColor="Black" />

        <local:DraggableView x:Name="dragView" DragMode="LongPress" DragDirection="All" >
            <local:DraggableView.Content>
                <BoxView x:Name="image" ItemSelected="Handle_ItemSelected" />
            </local:DraggableView.Content>
        </local:DraggableView>
    </Grid>

</ContentPage>

helper

public enum DragDirectionType
{
    All,
    Vertical,
    Horizontal
}
public enum DragMode
{
    Touch,
    LongPress
}

DraggableView

 public partial class DraggableView : ContentView
    {
        public event EventHandler DragStart = delegate { };
        public event EventHandler DragEnd = delegate { };

        public static readonly BindableProperty DragDirectionProperty = BindableProperty.Create(
            propertyName: "DragDirection",
            returnType: typeof(DragDirectionType),
            declaringType: typeof(DraggableView),
            defaultValue: DragDirectionType.All,
            defaultBindingMode: BindingMode.TwoWay);

        public DragDirectionType DragDirection
        {
            get { return (DragDirectionType)GetValue(DragDirectionProperty); }
            set { SetValue(DragDirectionProperty, value); }
        }


        public static readonly BindableProperty DragModeProperty = BindableProperty.Create(
           propertyName: "DragMode",
           returnType: typeof(DragMode),
           declaringType: typeof(DraggableView),
           defaultValue: DragMode.LongPress,
           defaultBindingMode: BindingMode.TwoWay);

        public DragMode DragMode
        {
            get { return (DragMode)GetValue(DragModeProperty); }
            set { SetValue(DragModeProperty, value); }
        }

        public static readonly BindableProperty IsDraggingProperty = BindableProperty.Create(
          propertyName: "IsDragging",
          returnType: typeof(bool),
          declaringType: typeof(DraggableView),
          defaultValue: false,
          defaultBindingMode: BindingMode.TwoWay);

        public bool IsDragging
        {
            get { return (bool)GetValue(IsDraggingProperty); }
            set { SetValue(IsDraggingProperty, value); }
        }


        public void DragStarted()
        {
            DragStart(this, default(EventArgs));
            IsDragging = true;
        }

        public void DragEnded()
        {
            IsDragging = false;
            DragEnd(this, default(EventArgs));
        }

    }
}

这是代码的android部分

[assembly: ExportRenderer(typeof(DraggableView), typeof(DraggableViewRenderer))]

namespace BabakusXamarin.Droid
{
    public class DraggableViewRenderer : VisualElementRenderer<Xamarin.Forms.View>
    {
        float originalX;
        float originalY;
        float dX;
        float dY;
        bool firstTime = true;
        bool touchedDown = false;

        protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.View> e)
        {
            base.OnElementChanged(e);


            if (e.OldElement != null)
            {
                LongClick -= HandleLongClick;
            }
        }

        private void HandleLongClick(object sender, LongClickEventArgs e)
        {
            var dragView = Element as DraggableView;
            if (firstTime)
            {
                originalX = GetX();
                originalY = GetY();
                firstTime = false;
            }
            dragView.DragStarted();
            touchedDown = true;
        }

        protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            var dragView = Element as DraggableView;
            base.OnElementPropertyChanged(sender, e);

        }
        protected override void OnVisibilityChanged(AView.View changedView, [GeneratedEnum] ViewStates visibility)
        {
            base.OnVisibilityChanged(changedView, visibility);
            if (visibility == ViewStates.Visible)
            {



            }
        }
        public override bool OnTouchEvent(MotionEvent e)
        {
            float x = e.RawX;
            float y = e.RawY;
            var dragView = Element as DraggableView;
            switch (e.Action)
            {
                case MotionEventActions.Down:
                    if (dragView.DragMode == DragMode.Touch)
                    {
                        if (!touchedDown)
                        {
                            if (firstTime)
                            {
                                originalX = GetX();
                                originalY = GetY();
                                firstTime = false;
                            }
                            dragView.DragStarted();
                        }

                        touchedDown = true;
                    }
                    dX = x - this.GetX();
                    dY = y - this.GetY();
                    break;
                case MotionEventActions.Move:
                    if (touchedDown)
                    {
                        if (dragView.DragDirection == DragDirectionType.All || dragView.DragDirection == DragDirectionType.Horizontal)
                        {
                            SetX(x - dX);
                        }

                        if (dragView.DragDirection == DragDirectionType.All || dragView.DragDirection == DragDirectionType.Vertical)
                        {
                            SetY(y - dY);
                        }

                    }
                    break;
                case MotionEventActions.Up:
                    touchedDown = false;
                    dragView.DragEnded();
                    break;
                case MotionEventActions.Cancel:
                    touchedDown = false;
                    break;
            }
            return base.OnTouchEvent(e);
        }

        public override bool OnInterceptTouchEvent(MotionEvent e)
        {

            BringToFront();
            return true;
        }

    }


}

最佳答案

问题在于可拖动视图，在代码local:draggableview的第一部分中，程序在代码的Xaml部分崩溃，但是我无法弄清楚问题出在哪里。

问题是:ItemSelected中没有BoxView。通过删除ItemSelected="ItemSelected"，您的xaml代码将起作用。

有关BoxView的详细信息，请参考BoxView。