c# – 在调整子级大小时保持scrollviewer的相对滚动条偏移量

//variables to store the offset values
    double relX;
    double relY;
    void scrollViewer1_ScrollChanged(object sender,ScrollChangedEventArgs e)
    {
        ScrollViewer scroll = sender as ScrollViewer;
        //see if the content size is changed
        if (e.ExtentWidthChange != 0 || e.ExtentHeightChange != 0)
        {
            //calculate and set accordingly
            scroll.ScrollToHorizontalOffset(CalculateOffset(e.ExtentWidth,e.ViewportWidth,scroll.ScrollableWidth,relX));
            scroll.ScrollToVerticalOffset(CalculateOffset(e.ExtentHeight,e.ViewportHeight,scroll.ScrollableHeight,relY));
        }
        else
        {
            //store the relative values if normal scroll
            relX = (e.HorizontalOffset + 0.5 * e.ViewportWidth) / e.ExtentWidth;
            relY = (e.VerticalOffset + 0.5 * e.ViewportHeight) / e.ExtentHeight;
        }
    }

    private static double CalculateOffset(double extent,double viewPort,double scrollWidth,double relBefore)
    {
        //calculate the new offset
        double offset = relBefore * extent - 0.5 * viewPort;
        //see if it is negative because of initial values
        if (offset < 0)
        {
            //center the content
            //this can be set to 0 if center by default is not needed
            offset = 0.5 * scrollWidth;
        }
        return offset;
    }

后面的想法是存储最后一个滚动位置,并在每次更改内容大小时使用它计算新的偏移量,这将使范围发生变化.

只需将ScrollViewer的事件ScrollChanged附加到构造函数等中的此事件处理程序,并将其余部分保留给它.

例如

scrollViewer1.ScrollChanged += scrollViewer1_ScrollChanged;

上述解决方案将确保将电网保持在中心位置,即使是第一次负载也是如此

中心内容的样本

放大了

缩小了

额外

我也尝试为同一个创建一个可附加的行为,因此您不需要连接事件,只需设置属性将启用或禁用该行为

namespace CSharpWPF
{
    public class AdvancedZooming : DependencyObject
    {
        public static bool GetKeepInCenter(DependencyObject obj)
        {
            return (bool)obj.GetValue(KeepInCenterProperty);
        }

        public static void SetKeepInCenter(DependencyObject obj,bool value)
        {
            obj.SetValue(KeepInCenterProperty,value);
        }

        // Using a DependencyProperty as the backing store for KeepInCenter.  This enables animation,styling,binding,etc...
        public static readonly DependencyProperty KeepInCenterProperty =
            DependencyProperty.RegisterAttached("KeepInCenter",typeof(bool),typeof(AdvancedZooming),new PropertyMetadata(false,OnKeepInCenterChanged));

        // Using a DependencyProperty as the backing store for Behavior.  This enables animation,etc...
        public static readonly DependencyProperty BehaviorProperty =
            DependencyProperty.RegisterAttached("Behavior",new PropertyMetadata(null));

        private static void OnKeepInCenterChanged(DependencyObject d,DependencyPropertyChangedEventArgs e)
        {
            ScrollViewer scroll = d as ScrollViewer;

            if ((bool)e.NewValue)
            {
                //attach the behavior
                AdvancedZooming behavior = new AdvancedZooming();
                scroll.ScrollChanged += behavior.scroll_ScrollChanged;
                scroll.SetValue(BehaviorProperty,behavior);
            }
            else
            {
                //dettach the behavior
                AdvancedZooming behavior = scroll.GetValue(BehaviorProperty) as AdvancedZooming;
                if (behavior != null)
                    scroll.ScrollChanged -= behavior.scroll_ScrollChanged;
                scroll.SetValue(BehaviorProperty,null);
            }
        }

        //variables to store the offset values
        double relX;
        double relY;
        void scroll_ScrollChanged(object sender,ScrollChangedEventArgs e)
        {
            ScrollViewer scroll = sender as ScrollViewer;
            //see if the content size is changed
            if (e.ExtentWidthChange != 0 || e.ExtentHeightChange != 0)
            {
                //calculate and set accordingly
                scroll.ScrollToHorizontalOffset(CalculateOffset(e.ExtentWidth,relX));
                scroll.ScrollToVerticalOffset(CalculateOffset(e.ExtentHeight,relY));
            }
            else
            {
                //store the relative values if normal scroll
                relX = (e.HorizontalOffset + 0.5 * e.ViewportWidth) / e.ExtentWidth;
                relY = (e.VerticalOffset + 0.5 * e.ViewportHeight) / e.ExtentHeight;
            }
        }

        private static double CalculateOffset(double extent,double relBefore)
        {
            //calculate the new offset
            double offset = relBefore * extent - 0.5 * viewPort;
            //see if it is negative because of initial values
            if (offset < 0)
            {
                //center the content
                //this can be set to 0 if center by default is not needed
                offset = 0.5 * scrollWidth;
            }
            return offset;
        }
    }
}

启用行为

通过xaml

<ScrollViewer l:AdvancedZooming.KeepInCenter="True">

要么

<Style TargetType="ScrollViewer" x:Key="zoomCenter">
    <Setter Property="l:AdvancedZooming.KeepInCenter"
            Value="True" />
</Style>

或者通过像

scrollViewer1.SetValue(AdvancedZooming.KeepInCenterProperty,true);

要么

AdvancedZooming.SetKeepInCenter(scrollViewer1,true);

通过样式或以编程方式设置属性l：AdvancedZooming.KeepInCenter =“True”内联,以便在任何scrollviewer上启用行为

l：在本例中指的是AdvancedZooming类的命名空间xmlns：l =“clr-namespace：CSharpWPF”