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 UserControl ，其中包含一个 TextBox 。当用户控件变得可见时，我将重点放在 TextBox 上。有人可以弄清楚为什么我必须使用 Dispatcher 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（无效）：

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

推荐答案

可以您在 InputTextBox.IsVisibleChanged 而不是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?

如果这行得通，那么我怀疑在布局面板更新子控件之前引发 this.IsVisibleChanged 事件，即当您将焦点放在没有 BeginInvoke 的 InputTextBox 上仍然不可见。

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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