c# - 如何检测取消 FormClosing 事件的父表单？

Question

我从主窗体中打开了一个子窗体，如下所示:

var cf = new ChildForm { Owner = this };
cf.Show();

然后子窗体在另一个线程上进行一些绘制。

当用户试图关闭主窗体时 - 如果子窗体处于打开状态 - 那么 FormClosing事件首先在 ChildForm 中触发，然后在主窗体中引发相同的事件。在 FormClosing 事件中，子窗体停止其绘图线程。

当主窗体包含未保存的数据时，用户可能会尝试关闭主窗体。然后主窗体的 FormClosing 事件处理程序向他们显示警告“数据未保存。取消关闭？”。然后他们可以取消保存(即 Cancel 标志由主窗体的 FormClosing 事件处理程序设置在 FormClosingEventArgs 对象上)。

但是，到那时，子窗体的 FormClosing 事件已经被引发，并且它将停止其绘图线程。子窗体不知道它现在应该继续绘制(就好像什么都没发生过一样)。

是否可以从子窗体中检测到 FormClosing 事件已被主窗体取消？当要求用户在主窗体中保存数据时，我仍然想停止重绘线程。

Answer 1

我会提供一个基于接口(interface)的解决方案。通过这种方式，您可以很容易地有一个统一的方式来管理应用程序是否可以关闭。通过以下实现，父窗体负责询问子窗口是否准备好关闭，子窗口执行任何必须执行的操作并回复主窗口。

假设我有接口(interface)IManagedForm:

interface IManagedForm
{
    bool CanIBeClosed(Object someParams);
}

两种形式(Form1 和 ChildForm)都会实现它。

请注意，对于此示例，我以这种方式实例化 ChildForm:

ChildForm cf = new ChildForm() { Owner = this, Name = "ChildForm" };
cf.Show();

首先是Form1接口(interface)的实现:

private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
    object someArgsInterestingForTheMethod = new object();

    e.Cancel = !((IManagedForm)this).CanIBeClosed(someArgsInterestingForTheMethod);
}

// Ask the ChildForm it is done. If not the user should not leave the application.
public bool CanIBeClosed(object someParams)
{
    bool isOKforClosing = true;

    var cf = this.Controls["ChildForm"] as IManagedForm;

    if (cf != null)
    {
        isOKforClosing = cf.CanIBeClosed(someParams);
        if (!isOKforClosing)
        {
            MessageBox.Show("ChildForm does not allow me to close.", "Form1", MessageBoxButtons.OK);
        }
    }
    return isOKforClosing;
}

最后，接口(interface)的 ChildForm 实现 将如下所示:

private void ChildForm_FormClosing(object sender, FormClosingEventArgs e)
{
    object someArgsInterestingForTheMethod = new object();

    e.Cancel = !((IManagedForm)this).CanIBeClosed(someArgsInterestingForTheMethod);
}

public bool CanIBeClosed(object someParams)
{
    // This flag would control if this window has not pending changes.
    bool meetConditions = ValidateClosingConditions(someParams);
    // If there were pending changes, but the user decided to not discard
    // them an proceed saving, this flag says to the parent that this form
    // is done, therefore is ready to be closed.
    bool iAmReadyToBeClosed = true;

    // There are unsaved changed. Ask the user what to do.
    if (!meetConditions)
    {
        // YES => OK Save pending changes and exit.
        // NO => Do not save pending changes and exit.
        // CANCEL => Cancel closing, just do nothing.
        switch (MessageBox.Show("Save changes before exit?", "MyChildForm", MessageBoxButtons.YesNoCancel, MessageBoxIcon.Question))
        {
            case DialogResult.Yes:
                // Store data and leave...
                iAmReadyToBeClosed = true;
                break;
            case DialogResult.No:
                // Do not store data, just leave...
                iAmReadyToBeClosed = true;
                break;
            case DialogResult.Cancel:
                // Do not leave...
                iAmReadyToBeClosed = false;
                break;
        }
    }
    return iAmReadyToBeClosed;
}

// This is just a dummy method just for testing
public bool ValidateClosingConditions(object someParams)
{
    Random rnd = new Random();
    return ((rnd.Next(10) % 2) == 0);
}

希望它足够清楚。