MDI 窗体中的消息框在应用程序关闭之前多次显示

我知道即使在StackOverflow中也有类似问题的例子，但我很难理解问题的本质，因此很难解决我的自定义情况。

我现在拥有的是这段代码：

bool closingPending = false;
private void MyFormN_FormClosing(object sender, FormClosingEventArgs e)
        {
            if (closingPending) return;
            //DialogResult answer = MessageBox.Show("Do you want to save changes ?", "Save",
            if (MessageBox.Show("Do you want to save changes ?", "Save",
                                   MessageBoxButtons.YesNoCancel,
                                   MessageBoxIcon.Information,
                                   MessageBoxDefaultButton.Button3) == DialogResult.Yes)
            {
                closingPending = true;
                MessageBox.Show("To Do - validate and save");
            }
            if (MessageBox.Show("Do you want to save changes ?", "Save",
                                   MessageBoxButtons.YesNoCancel,
                                   MessageBoxIcon.Information,
                                   MessageBoxDefaultButton.Button3) == DialogResult.Cancel)
            {
                closingPending = true;
                e.Cancel = true;
            }
            if (MessageBox.Show("Do you want to save changes ?", "Save",
                                   MessageBoxButtons.YesNoCancel,
                                   MessageBoxIcon.Information,
                                   MessageBoxDefaultButton.Button3) == DialogResult.No)
            {
                closingPending = true;
                 Application.Exit();
            }
        }

这是我的尝试和我从这里其他帖子中获得的一些想法的结果。但是当我执行此代码时发生的情况是 - 通过按窗口的[x]，我会显示消息框，但无论我单击哪个按钮，表单都会显示几次。在添加closingPending之前，我很确定此问题仅在我尝试Application.Exit()时才发生。当我尝试此示例时，closingPending示例有效：

if(closingPending) return;
if (MessageBox.Show("This application is closing down because of " + e.CloseReason.ToString() + ". Do you really want to close it ?", "", MessageBoxButtons.YesNo) == DialogResult.No)
    {                
        e.Cancel = true;
    }
    else
    {
        closingPending = true;
        Application.Exit();
    }

但是，我对导致问题的原因有一些想法，但我离完全理解或解决它还很远。

DialogResult result = MessageBox.Show("Do you want to save changes ?", "Save",
                                   MessageBoxButtons.YesNoCancel,
                                   MessageBoxIcon.Information,
                                   MessageBoxDefaultButton.Button3);
            switch (result)
            {
                case DialogResult.Yes: 
                    closingPending = true;
                    MessageBox.Show("To Do - validate and save");
                    break;
                case DialogResult.No: 
                    closingPending = true;
                    Application.Exit();
                    break;
                case DialogResult.Cancel:
                    closingPending = true;
                    e.Cancel = true;
                    break;
            }