WPF Scrollviewer 不适应内容

Question

我需要在我的 WPF 应用程序中显示一个图像，用透明画布覆盖它并允许用户在其上绘图。用户必须能够缩放图像（放大和缩小）和“导航”图像，同时使用停靠在窗口底部和右侧的某种滚动条进行放大。为了启用图像缩放，我使用了ZoomBorder control，在第二个答案中进行了描述。这是我的 XAML 代码：

<ScrollViewer x:Name="imageScroll" HorizontalScrollBarVisibility="Auto" VerticalScrollBarVisibility="Auto"  >
  <local:ZoomBorder x:Name="backgroundZoomBorder" ClipToBounds="True" HorizontalAlignment="Center" VerticalAlignment="Center"  Width="{Binding CurrentImageWidth}" Height="{Binding CurrentImageHeight}"  >
     <Grid x:Name="gridDrawing" MouseLeftButtonDown="background_MouseLeftButtonDown" MouseMove="background_MouseMove" MouseLeftButtonUp="background_MouseLeftButtonUp">                           
       <Image  x:Name="mainImage"  Source="{Binding Path=WriteableBmp}" />
       <Canvas x:Name="canvasDrawing"  Background="Transparent" />
     </Grid>
  </local:ZoomBorder>
</ScrollViewer>

这可行，但是，scollviewer 不会调整内容的大小，如果图像放大到最大，或者缩小到最小，它仍然是一样的。如果图像小于窗口区域，它应该消失，或者在图像缩放时具有更大的范围。我可以无论如何将 ScrollViever 绑定到 Image 的转换大小或其他东西吗？或者有没有更好的控制来代替ScrollViewer？ 谢谢

Answer 1

ScrollViewer 永远不会与ZoomBorder 控件一起使用，因为它使用的是RenderTransform。 RenderTransform 会操纵您在通过布局系统后看到的内容。因此，它的大小永远不会改变，因此ScrollViewer 永远不会激活。

通过将ZoomBorder 修改为使用LayoutTransform，您可以获得缩放（滚轮）功能并且ScrollViewer 将激活。但是，要使用鼠标进行平移需要进行更多重大修改。

以下是一些有效的示例代码：

使用 LayoutTransform 的 ZoomBorder

using System.Linq;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Media;

namespace SO
{
    public class ZoomBorder : Border
    {
        private FrameworkElement child;

        private ScaleTransform GetScaleTransform(FrameworkElement element)
        {
            return (ScaleTransform)((TransformGroup)element.LayoutTransform)
              .Children.First(tr => tr is ScaleTransform);
        }

        public override UIElement Child
        {
            get => base.Child;
            set
            {
                if (value != null && value != Child)
                    Initialize(value);
                base.Child = value;
            }
        }

        public void Initialize(UIElement element)
        {
            child = (FrameworkElement)element;

            if (child == null) return;

            var group = new TransformGroup();
            var st = new ScaleTransform();

            @group.Children.Add(st);

            child.LayoutTransform = @group;
            child.RenderTransformOrigin = new Point(0.0, 0.0);

            MouseWheel += child_MouseWheel;
            PreviewMouseRightButtonDown += child_PreviewMouseRightButtonDown;
        }

        public void Reset()
        {
            if (child == null) return;

            // reset zoom
            var st = GetScaleTransform(child);
            st.ScaleX = 1.0;
            st.ScaleY = 1.0;
        }

        #region Child Events
        private void child_MouseWheel(object sender, MouseWheelEventArgs e)
        {
            if (child != null)
            {
                var st = GetScaleTransform(child);

                var zoom = e.Delta > 0 ? .2 : -.2;

                if (!(e.Delta > 0) && (st.ScaleX < .4 || st.ScaleY < .4)) return;

                st.ScaleX += zoom;
                st.ScaleY += zoom;
            }
        }

        void child_PreviewMouseRightButtonDown(object sender, MouseButtonEventArgs e)
        {
            Reset();
        }
        #endregion
    }
}

ScrollViewerPanBehavior 一种通过鼠标拖动来处理平移的行为。

using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Interactivity;

namespace SO
{
    public class ScrollViewerPanBehavior : Behavior<ScrollViewer>
    {
        private UIElement content;
        private Point scrollMousePoint;
        private double scrollHorizontalOffset;
        private double scrollVerticalOffset;

        public ScrollViewerPanBehavior()
        {
        }

        protected override void OnAttached()
        {
            base.OnAttached();
            AssociatedObject.Loaded += OnLoaded;
        }

        private void OnLoaded(object sender, RoutedEventArgs e)
        {
            content = (UIElement)AssociatedObject.Content;
            content.MouseLeftButtonDown += OnMouseLeftButtonDown;
            content.MouseMove += OnMouseMove;
            content.MouseLeftButtonUp += OnMouseLeftButtonUp;
        }

        private void OnMouseLeftButtonDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            content.CaptureMouse();
            AssociatedObject.Cursor = Cursors.Hand;
            scrollMousePoint = e.GetPosition(AssociatedObject);
            scrollHorizontalOffset = AssociatedObject.HorizontalOffset;
            scrollVerticalOffset = AssociatedObject.VerticalOffset;
        }

        private void OnMouseMove(object sender, System.Windows.Input.MouseEventArgs e)
        {
            if (content.IsMouseCaptured)
            {
                var newVerticalOffset = scrollVerticalOffset + (scrollMousePoint.Y - e.GetPosition(AssociatedObject).Y);
                var newHorizontalOffset = scrollHorizontalOffset + (scrollMousePoint.X - e.GetPosition(AssociatedObject).X);

                AssociatedObject.ScrollToVerticalOffset(newVerticalOffset);
                AssociatedObject.ScrollToHorizontalOffset(newHorizontalOffset);
            }
        }

        private void OnMouseLeftButtonUp(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            content.ReleaseMouseCapture();
            AssociatedObject.Cursor = Cursors.Arrow;
        }
    }
}

示例用法：

<ScrollViewer
    HorizontalScrollBarVisibility="Auto"
    VerticalScrollBarVisibility="Auto">
    <i:Interaction.Behaviors>
        <local:ScrollViewerPanBehavior />
    </i:Interaction.Behaviors>
    <local:ZoomBorder
        HorizontalAlignment="Center"
        VerticalAlignment="Center">
        <Grid>
            <Image Source="ThumbsUp.png" />
        </Grid>
    </local:ZoomBorder>
</ScrollViewer>

这很有趣！