为什么从后面的代码设置键盘焦点需要 Dispatcher.BeginInvoke?

Why does setting keyboard focus from code behind require Dispatcher.BeginInvoke?(为什么从后面的代码设置键盘焦点需要 Dispatcher.BeginInvoke?)

问题描述

我有一个包含 TextBox 的 UserControl.当用户控件变得可见时，我将焦点放在 TextBox 上.有人可以澄清为什么我必须使用 Dispatcher 来执行此操作吗?

I have a UserControl that contains a TextBox. When the user control becomes visible, I give the TextBox focus. Could somebody clarify why I have to do this using the Dispatcher?

public MyUserControl() 
{
    InitializeComponent();
    this.IsVisibleChanged += VisibilityChanged;
}

案例 1(有效):

private void VisibilityChanged(object sender, DependencyPropertyChangedEventArgs e)
{
    if (this.Visibility == Visibility.Visible)
    {
        this.Dispatcher.BeginInvoke((Action)delegate
        {
            Keyboard.Focus(this.InputTextBox);
        }, DispatcherPriority.Render);
    }
}

案例2(不起作用):

private void VisibilityChanged(object sender, DependencyPropertyChangedEventArgs e)
{
    if (this.Visibility == Visibility.Visible)
    {
        Keyboard.Focus(InputTextBox);
    }
}

推荐答案

你能不能在 InputTextBox.IsVisibleChanged 的事件处理程序中调用 Keyboard.Focus(InputTextBox);this.IsVisibleChanged?

could you call Keyboard.Focus(InputTextBox); in the event handler for InputTextBox.IsVisibleChanged instead of this.IsVisibleChanged?

如果这可行，那么我怀疑在布局面板更新子控件之前引发了 this.IsVisibleChanged 事件，即当您放置时，可能 InputTextBox 仍然不可见在没有 BeginInvoke 的情况下专注于它.

If this works then I suspect the this.IsVisibleChanged event is raised before the layout panel has updated the children controls, i.e perhaps InputTextBox is still not visible when you put focus on it without BeginInvoke.

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