解决 Popup 位置不随窗口移动更新的问题

Popup弹出后，因业务需求设置了StaysOpen=true后，移动窗口位置或者改变窗口大小，Popup的位置不会更新。

如何更新位置？

获取当前Popup的Target绑定UserControl所在窗口，位置刷新时，时时更新Popup的位置即可。

1.添加一个附加属性

 /// <summary>
 /// Popup位置更新
 /// </summary>
 public static readonly DependencyProperty PopupPlacementTargetProperty =
     DependencyProperty.RegisterAttached("PopupPlacementTarget", typeof(DependencyObject), typeof(PopupHelper), new PropertyMetadata(null, OnPopupPlacementTargetChanged));

2.窗口移动后触发popup更新

首先，有个疑问，popup首次显示时，为何显示的位置是正确的呢？

通过查看源码，发现，其实popup也是有内置更新popup位置的！

而通过查看UpdatePosition代码，其方法确实是更新popup位置的。源码如下：

 private void UpdatePosition()
 {
     if (this._popupRoot.Value == null)
         return;
     PlacementMode placement = this.Placement;
     Point[] targetInterestPoints = this.GetPlacementTargetInterestPoints(placement);
     Point[] childInterestPoints = this.GetChildInterestPoints(placement);
     Rect bounds = this.GetBounds(targetInterestPoints);
     Rect rect1 = this.GetBounds(childInterestPoints);
     double num1 = rect1.Width * rect1.Height;
     int num2 = -;
     Vector offsetVector1 = new Vector((double)this._positionInfo.X, (double)this._positionInfo.Y);
     double num3 = -1.0;
     PopupPrimaryAxis popupPrimaryAxis = PopupPrimaryAxis.None;
     CustomPopupPlacement[] customPopupPlacementArray = (CustomPopupPlacement[])null;
     int num4;
     if (placement == PlacementMode.Custom)
     {
         CustomPopupPlacementCallback placementCallback = this.CustomPopupPlacementCallback;
         if (placementCallback != null)
             customPopupPlacementArray = placementCallback(rect1.Size, bounds.Size, new Point(this.HorizontalOffset, this.VerticalOffset));
         num4 = customPopupPlacementArray == null ?  : customPopupPlacementArray.Length;
         if (!this.IsOpen)
             return;
     }
     else
         num4 = Popup.GetNumberOfCombinations(placement);
     for (int i = ; i < num4; ++i)
     {
         bool flag1 = false;
         bool flag2 = false;
         Vector offsetVector2;
         PopupPrimaryAxis axis;
         if (placement == PlacementMode.Custom)
         {
             offsetVector2 = (Vector)targetInterestPoints[] + (Vector)customPopupPlacementArray[i].Point;
             axis = customPopupPlacementArray[i].PrimaryAxis;
         }
         else
         {
             Popup.PointCombination pointCombination = this.GetPointCombination(placement, i, out axis);
             Popup.InterestPoint targetInterestPoint = pointCombination.TargetInterestPoint;
             Popup.InterestPoint childInterestPoint = pointCombination.ChildInterestPoint;
             offsetVector2 = targetInterestPoints[(int)targetInterestPoint] - childInterestPoints[(int)childInterestPoint];
             flag1 = childInterestPoint == Popup.InterestPoint.TopRight || childInterestPoint == Popup.InterestPoint.BottomRight;
             flag2 = childInterestPoint == Popup.InterestPoint.BottomLeft || childInterestPoint == Popup.InterestPoint.BottomRight;
         }
         Rect rect2 = Rect.Offset(rect1, offsetVector2);
         Rect rect3 = Rect.Intersect(this.GetScreenBounds(bounds, targetInterestPoints[]), rect2);
         double num5 = rect3 != Rect.Empty ? rect3.Width * rect3.Height : 0.0;
         if (num5 - num3 > 0.01)
         {
             num2 = i;
             offsetVector1 = offsetVector2;
             num3 = num5;
             popupPrimaryAxis = axis;
             this.AnimateFromRight = flag1;
             this.AnimateFromBottom = flag2;
             if (Math.Abs(num5 - num1) < 0.01)
                 break;
         }
     }
     if (num2 >=  && (placement == PlacementMode.Right || placement == PlacementMode.Left))
         this.DropOpposite = !this.DropOpposite;
     rect1 = new Rect((Size)this._secHelper.GetTransformToDevice().Transform((Point)this._popupRoot.Value.RenderSize));
     rect1.Offset(offsetVector1);
     Rect screenBounds = this.GetScreenBounds(bounds, targetInterestPoints[]);
     Rect rect4 = Rect.Intersect(screenBounds, rect1);
     if (Math.Abs(rect4.Width - rect1.Width) > 0.01 || Math.Abs(rect4.Height - rect1.Height) > 0.01)
     {
         Point point1 = targetInterestPoints[];
         Vector vector1 = targetInterestPoints[] - point1;
         vector1.Normalize();
         if (!this.IsTransparent || double.IsNaN(vector1.Y) || Math.Abs(vector1.Y) < 0.01)
         {
             if (rect1.Right > screenBounds.Right)
                 offsetVector1.X = screenBounds.Right - rect1.Width;
             else if (rect1.Left < screenBounds.Left)
                 offsetVector1.X = screenBounds.Left;
         }
         else if (this.IsTransparent && Math.Abs(vector1.X) < 0.01)
         {
             if (rect1.Bottom > screenBounds.Bottom)
                 offsetVector1.Y = screenBounds.Bottom - rect1.Height;
             else if (rect1.Top < screenBounds.Top)
                 offsetVector1.Y = screenBounds.Top;
         }
         Point point2 = targetInterestPoints[];
         Vector vector2 = point1 - point2;
         vector2.Normalize();
         if (!this.IsTransparent || double.IsNaN(vector2.X) || Math.Abs(vector2.X) < 0.01)
         {
             if (rect1.Bottom > screenBounds.Bottom)
                 offsetVector1.Y = screenBounds.Bottom - rect1.Height;
             else if (rect1.Top < screenBounds.Top)
                 offsetVector1.Y = screenBounds.Top;
         }
         else if (this.IsTransparent && Math.Abs(vector2.Y) < 0.01)
         {
             if (rect1.Right > screenBounds.Right)
                 offsetVector1.X = screenBounds.Right - rect1.Width;
             else if (rect1.Left < screenBounds.Left)
                 offsetVector1.X = screenBounds.Left;
         }
     }
     int x = DoubleUtil.DoubleToInt(offsetVector1.X);
     int y = DoubleUtil.DoubleToInt(offsetVector1.Y);
     if (x == this._positionInfo.X && y == this._positionInfo.Y)
         return;
     this._positionInfo.X = x;
     this._positionInfo.Y = y;
     this._secHelper.SetPopupPos(true, x, y, false, , );
 }

那么，我们有什么办法调用这个私有方法呢？我相信大家都想，找到popup源码开发者，爆了他Y的！

有一种方法，叫反射，反射可以获取类的任一个字段或者属性。

反射，可以参考：https://www.cnblogs.com/vaevvaev/p/6995639.html

通过反射，我们获取到UpdatePosition方法，并调用执行。

 var mi = typeof(Popup).GetMethod("UpdatePosition", BindingFlags.NonPublic | BindingFlags.Instance);
 mi.Invoke(pop, null);

下面是详细的属性更改事件实现：

     private static void OnPopupPlacementTargetChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
     {
         Popup pop = d as Popup;
         //旧值取消LocationChanged监听
         if (e.OldValue is DependencyObject previousPlacementTarget)
         {
             Window window = Window.GetWindow(previousPlacementTarget);
             var element = previousPlacementTarget as FrameworkElement;
             if (window != null)
             {
                 CancelEventsListeningInWindow(window);
             }
             if (element != null)
             {
                 element.SizeChanged -= ElementSizeChanged;
                 element.LayoutUpdated -= ElementLayoutUpdated;
             }
         }

         //新值添加LocationChanged监听
         if (e.NewValue is DependencyObject newPlacementTarget)
         {
             Window window = Window.GetWindow(newPlacementTarget);
             var element = newPlacementTarget as FrameworkElement;
             //窗口已加载
             if (window != null)
             {
                 RegisterEventsInWindow(window);
             }
             //窗口未加载，则等待控件初始化后，再获取窗口
             else if (element != null)
             {
                 element.Loaded -= ElementLoaded;
                 element.Loaded += ElementLoaded;
             }
             //元素大小变换时，变更Popup位置
             if (element != null)
             {
                 element.SizeChanged -= ElementSizeChanged;
                 element.SizeChanged += ElementSizeChanged;
                 element.LayoutUpdated -= ElementLayoutUpdated;
                 element.LayoutUpdated += ElementLayoutUpdated;
             }
             void ElementLoaded(object sender, RoutedEventArgs e3)
             {
                 element.Loaded -= ElementLoaded;
                 window = Window.GetWindow(newPlacementTarget);
                 if (window != null)
                 {
                     RegisterEventsInWindow(window);
                 }
             }
         }
         void RegisterEventsInWindow(Window window)
         {
             window.LocationChanged -= WindowLocationChanged;
             window.LocationChanged += WindowLocationChanged;
             window.SizeChanged -= WindowSizeChanged;
             window.SizeChanged += WindowSizeChanged;
         }
         void CancelEventsListeningInWindow(Window window)
         {
             window.LocationChanged -= WindowLocationChanged;
             window.SizeChanged -= WindowSizeChanged;
         }
         void WindowLocationChanged(object s1, EventArgs e1)
         {
             UpdatePopupLocation();
         }
         void WindowSizeChanged(object sender, SizeChangedEventArgs e2)
         {
             UpdatePopupLocation();
         }
         void ElementSizeChanged(object sender, SizeChangedEventArgs e3)
         {
             UpdatePopupLocation();
         }
         void ElementLayoutUpdated(object sender, EventArgs e4)
         {
             UpdatePopupLocation();
         }
         void UpdatePopupLocation()
         {
             if (pop != null && pop.IsOpen)
             {
                 //通知更新相对位置
                 var method = typeof(Popup).GetMethod("UpdatePosition", BindingFlags.NonPublic | BindingFlags.Instance);
                 method?.Invoke(pop, null);
             }
         }
     }

值得注意的是，原有的绑定目标源要记得取消LocationChanged事件订阅，新的绑定目标源保险起见，也要提前注销再添加事件订阅。

另：通知popup位置更新，也可能通过如下的黑科技：

     //通知更新相对位置
     var offset = pop.HorizontalOffset;
     pop.HorizontalOffset = offset + ;
     pop.HorizontalOffset = offset;

为何改变一下HorizontalOffset就可行呢？因为上面最终并没有改变HorizontalOffset的值。。。

原来。。。好吧，先看源码

     /// <summary>获取或设置目标原点和弹出项对齐之间的水平距离点。</summary>
     /// <returns>
     ///   目标原点和 popup 对齐点之间的水平距离。
     ///    有关目标原点和 popup 对齐点的信息，请参阅 Popup 放置行为。
     ///    默认值为 0。
     /// </returns>
     [Bindable(true)]
     [Category("Layout")]
     [TypeConverter(typeof (LengthConverter))]
     public double HorizontalOffset
     {
       get
       {
         return (double) this.GetValue(Popup.HorizontalOffsetProperty);
       }
       set
       {
         this.SetValue(Popup.HorizontalOffsetProperty, (object) value);
       }
     }

     private static void OnOffsetChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
     {
       ((Popup) d).Reposition();
     }

是的，最终调用了Reposition，而Reposition方法中有调用UpdatePosition更新popup位置。

所以以上，更新HorizontalOffset，是更新popup位置的一种捷径。

3. 元素移动/大小变化后，触发更新

当popup的PlaceTarget绑定一个控件或者一个Grid后，FrameworkElement大小变化/位置变化时，popup位置更新(同上)

元素大小变化时：

     else if (newPlacementTarget is FrameworkElement frameworkElement)
     {
         frameworkElement.SizeChanged -= ElementOnSizeChanged;
         frameworkElement.SizeChanged += ElementOnSizeChanged;
     }

也可以直接监听LayoutUpdated事件，元素大小/位置变化时，LayoutUpdated都会触发。注意：LayoutUpdated触发有点频繁。

     else if (newPlacementTarget is FrameworkElement frameworkElement)
     {
         frameworkElement.LayoutUpdated -= ElementOnLayoutUpdated;
         frameworkElement.LayoutUpdated += ElementOnLayoutUpdated;
     }

4.界面设置绑定目标源

     <Popup x:Name="FirstShowPopup" PlacementTarget="{Binding ElementName=TestButton}" Placement="Custom"
         CustomPopupPlacementCallback="{easiUi:Placement Align=RightCenter,OutOfScreenEnabled=True}" PopupAnimation="Fade"
         AllowsTransparency="True" StaysOpen="True" HorizontalOffset="-16" VerticalOffset="4"
         helper:PopupHelper.LocationUpdatedOnTarget="{Binding ElementName=TestButton}"
         helper:PopupHelper.TopmostInCurrentWindow="True">
     </Popup>