无法设置元素的焦点
我有一个 Expander，其内容由 StackPanel 组成，其中包含多个元素，其中一个元素是 TextBox。
我想，当 Expander 扩展 TextBox 时应该获得键盘焦点，我该怎么做？
我尝试过：
Private Sub xp_Expanded(sender As Object, e As RoutedEventArgs) _
Handles xpUnits.Expanded
stackPanel.Focus()
Keyboard.Focus(textBox)
textBox.Focus()
End Sub
我什至尝试将 FocusManager.IsFocusable 和 FocusManager.FocusedElement 设置为 TextBox，然后调用 stackPanel.Focus()，但它没有完成这项工作。
I have an Expander that its content consists of a StackPanel that contains several elements one of whom is a TextBox.
I want, that when the Expander expands that TextBox should gain keyboard focus, how do I do this?
I tried:
Private Sub xp_Expanded(sender As Object, e As RoutedEventArgs) _
Handles xpUnits.Expanded
stackPanel.Focus()
Keyboard.Focus(textBox)
textBox.Focus()
End Sub
I even tried to set FocusManager.IsFocusable and FocusManager.FocusedElement to the TextBox, then call stackPanel.Focus(), but it didn't do the job.
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评论（2）
当您尝试设置焦点时，您的
TextBox可能还不可见。您应该将IsVisibleChanged的事件处理程序添加到TextBox并在那里设置焦点。在 xp_Expanded 内，您只需设置一个布尔标志，以便下次调用 IsVisibleChanged 事件处理程序时应将焦点集中在TextBox上。Probably your
TextBoxis not yet visible when you try to set the focus. You should add an event handler forIsVisibleChangedto yourTextBoxand set the focus there. Insidexp_Expandedyou just should set a boolean flag that theTextBoxshould be focused the next time theIsVisibleChangedevent handler is called.这个答案解决了我的问题轻松发出：
This answer solved my issue easily: