C# Winforms - 使用 FormClosing 时，消息框未在 if 语句中打开

Question

我试图在按下表单上的“x”按钮时打开消息框；仅当满足特定条件时。我有以下代码：

bool uncommitted = false;

// Do something which sets uncommitted to true
...

// If uncommitted, open message box 
if (uncommitted)
{
    result = MessageBox.Show("Are you sure you want to exit?", "Testing",
                MessageBoxButtons.YesNo, MessageBoxIcon.Hand);

    if (result == DialogResult.No)
        e.Cancel = true;
}

编译完成后，当表单关闭时，表单会冻结并且鼠标光标加载圆圈出现。

如果我将消息框代码放在 if 语句之外，则消息框将按预期打开。

// This code opens the message box without any regard to the condition
...
result = MessageBox.Show("Are you sure you want to exit?", "Testing",
            MessageBoxButtons.YesNo, MessageBoxIcon.Hand);

if (result == DialogResult.No)
    e.Cancel = true;

if (uncommitted) {; }

知道为什么会发生这种情况吗？

Answer 1

此错误是由计时器和后台工作程序引起的，它们在

FormClosing()

时仍在运行。在调用

MessageBox.Show()

函数之前关闭这些进程解决了问题：

...

// Close processes
if (timer.enabled) timer.Stop();
if (backgroundWorker.IsBusy) backgroundworker.CancelAsync();

// Some code to determine state of uncommitted
...

// Open messagebox
if (uncommitted)
{
    result = MessageBox.Show("Are you sure you want to exit?", "Test",
                MessageBoxButtons.YesNo, MessageBoxIcon.Hand);

    if (result == DialogResult.No)
    { 
        e.Cancel = true;
        timer.Start();
        backgroundWorker.RunWorkerAsync();
    }
}

...