在WPF中，什么情况下不Visual.PointFromScreen抛出InvalidOperationException异常？ [英] In WPF, under what circumstances does Visual.PointFromScreen throw InvalidOperationException?

问题描述

假设我想做到这一点，这样我就可以找到鼠标相对于视觉，而无需访问特定的鼠标事件的当前位置：

Suppose I wanted to do this, so I can find the current position of the mouse relative to a Visual, without needing access to a specific mouse event:

public static Point GetMousePosition(this Visual relativeTo)
{
    return relativeTo.PointFromScreen(GetMousePositionOnScreen());
}

有时（通常当我只有两个选项卡控件之间切换） PointFromScreen 抛出 InvalidOperationException异常与消息此Visual未连接到presentationSource。的

在看属性可在视觉我看不到任何与一个 presentationSource

On looking at the properties available on Visual I can't see any relating to a PresentationSource.

给定一个视觉，我怎么能知道它是要扔的时候我称之为异常 PointFromScreen 上它？

Given a Visual, how can I tell if it is going to throw that exception when I call PointFromScreen on it?

推荐答案

有一个静态方法<一href="http://msdn.microsoft.com/en-us/library/system.windows.$p$psentationsource.fromvisual.aspx"><$c$c>$p$psentationSource.FromVisual其中：

There's a static method PresentationSource.FromVisual which:

返回其提供的可视化是presented源。

Returns the source in which a provided Visual is presented.

我知道这并不能解决根本问题，但你可以检查视觉连接至presentationSource之前调用 PointFromScreen 。它将prevent例外，但你需要做一些更多的研究，为什么它没有被连接在首位。

I know this doesn't solve the underlying problem, but you could check that the Visual is connected to a PresentationSource before calling PointFromScreen. It would prevent the exception, but you'd need to do some more investigation as to why it wasn't connected in the first place.

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