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>
