FireMonkey中如何判断拖动操作已经结束？
我想查明拖动的控件是否已在任何目标之外释放。
人们可能认为应该使用 OnDragEnd，但该事件不起作用（他们忘记在 FMX.Types 单元中调用 DragEnd 过程）。
作为替代方案，我尝试使用 OnMouseUp 来拖动控件。不起作用。当 DragMode=dmAutomatic 时不会触发。
作为最后的手段，我尝试重写表单本身的 MouseUp 过程（因为所有鼠标事件在传递到相应控件之前都会经过表单）。惊喜：当控件的 DragMode=dmAutomatic 时，不会调用 MouseUp 过程。
令人惊讶的是，如此简单的事情却很难实现，但我希望有人可能找到了可行的解决方案。
I want to find out if a dragged control has been released outside any target.
One would think that OnDragEnd should be used, but that event doesn't work (they forgot to call the DragEnd procedure in the FMX.Types unit).
As an alternative, I tried OnMouseUp for the dragged control. Doesn't work. Doesn't get triggered when DragMode=dmAutomatic.
As a last resort, I tried to override the MouseUp procedure of the form itself (since all mouse events go through the form before being handed down to the respective control). Surprise: the MouseUp procedure does not get called when the control's DragMode=dmAutomatic.
Amazing how something this very simple is this extremely hard to achieve, but I'm hoping someone might have found a working solution.
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可以重写表单的 DragLeave 方法。对于掉落到目标区域之外的所有对象，都会调用此方法。
It is possible to override the form's DragLeave method. This method is called for all objects that get dropped outside of a target area.