有没有办法捕捉 ContainsFocus 的变化？

Question

我需要能够确定ContainsFocus 何时在Control（特别是Windows 窗体）上发生变化。覆盖OnGotFocus 不是答案。当我将表单带到前台时，ContainsFocus 为真，Focused 为假。那么OnGotFocus 是否与ContainsFocus 等效？还是其他方式？

Answer 1

注意：如果您有子控件，则会触发子控件的 GotFocus 事件。否则调用表单的 OnGotFocus。

如果我正确理解了这个问题，那么这应该有效：

    bool lastNotificationWasGotFocus = false;

    protected override void OnControlAdded(ControlEventArgs e)
    {
        SubscribeEvents(e.Control);
        base.OnControlAdded(e);
    }

    protected override void OnControlRemoved(ControlEventArgs e)
    {
        UnsubscribeEvents(e.Control);
        base.OnControlRemoved(e);
    }

    private void SubscribeEvents(Control control)
    {
        control.GotFocus += new EventHandler(control_GotFocus);
        control.LostFocus += new EventHandler(control_LostFocus);
        control.ControlAdded += new ControlEventHandler(control_ControlAdded);
        control.ControlRemoved += new ControlEventHandler(control_ControlRemoved);

        foreach (Control innerControl in control.Controls)
        {
            SubscribeEvents(innerControl);
        }
    }

    private void UnsubscribeEvents(Control control)
    {
        control.GotFocus -= new EventHandler(control_GotFocus);
        control.LostFocus -= new EventHandler(control_LostFocus);
        control.ControlAdded -= new ControlEventHandler(control_ControlAdded);
        control.ControlRemoved -= new ControlEventHandler(control_ControlRemoved);

        foreach (Control innerControl in control.Controls)
        {
            UnsubscribeEvents(innerControl);
        }
    }

    private void control_ControlAdded(object sender, ControlEventArgs e)
    {
        SubscribeEvents(e.Control);
    }

    private void control_ControlRemoved(object sender, ControlEventArgs e)
    {
        UnsubscribeEvents(e.Control);
    }

    protected override void OnGotFocus(EventArgs e)
    {
        CheckContainsFocus();
        base.OnGotFocus(e);
    }

    protected override void OnLostFocus(EventArgs e)
    {
        CheckLostFocus();
        base.OnLostFocus(e);
    }

    private void control_GotFocus(object sender, EventArgs e)
    {
        CheckContainsFocus();
    }

    private void control_LostFocus(object sender, EventArgs e)
    {
        CheckLostFocus();
    }

    private void CheckContainsFocus()
    {
        if (lastNotificationWasGotFocus == false)
        {
            lastNotificationWasGotFocus = true;
            OnContainsFocus();
        }
    }

    private void CheckLostFocus()
    {
        if (ContainsFocus == false)
        {
            lastNotificationWasGotFocus = false;
            OnLostFocus();
        }
    }

    private void OnContainsFocus()
    {
        Console.WriteLine("I have the power of focus!");
    }

    private void OnLostFocus()
    {
        Console.WriteLine("I lost my power...");
    }

Answer 2

解决此问题的一种方法是使用计时器。这绝对是蛮力，但它可以完成工作：

private Timer m_checkContainsFocusTimer = new Timer();
private bool m_containsFocus = true;

m_checkContainsFocusTimer.Interval = 1000; // every second is good enough
m_checkContainsFocusTimer.Tick += new EventHandler(CheckContainsFocusTimer_Tick);
m_checkContainsFocusTimer.Start();

private void CheckContainsFocusTimer_Tick(object sender, EventArgs e)
{
    if (!m_containsFocus && ContainsFocus)
        OnAppGotFocus();

    m_containsFocus = ContainsFocus;
}

但是有没有更简单的方法？

Answer 3

应该处理 GotFocus 和 LostFocus 事件。

还有一点需要注意...... SDK 对 ContainsFocus 属性的描述如下：

您可以使用此属性来确定 无论是控制或任何 其中包含的控件具有 输入焦点。要确定是否 控制有焦点，不管 它的任何子控件是否有 焦点，使用 Focused 属性。

编辑：

在处理 GotFocus 事件时，您可能仍需要检查 Focused/ContainsFocus 属性，具体取决于控件层次结构的设置方式。

如果控件或其任何子控件具有焦点，

ContainsFocus 将为真。 仅当特定控件本身具有焦点时，焦点才会为真，无论其子控件如何。