Windows窗体中的跨线程调用有什么问题? [英] What's wrong with my cross-thread call in Windows Forms?

问题描述

我在Windows Forms应用程序中遇到问题.

I encounter a problem with a Windows Forms application.

必须从另一个线程显示一个表单.因此，在表单类中，我有以下代码:

A form must be displayed from another thread. So in the form class, I have the following code:

private delegate void DisplayDialogCallback();

public void DisplayDialog()
{
    if (this.InvokeRequired)
    {
        this.Invoke(new DisplayDialogCallback(DisplayDialog));
    }
    else
    {
        this.ShowDialog();
    }
}

现在，每次运行此命令时，都会在this.ShowDialog();行上抛出InvalidOperationException:

Now, every time I run this, an InvalidOperationException is thrown on the line this.ShowDialog();:

跨线程操作无效:控制'SampleForm'是从创建该线程的线程之外的线程访问的."

这段代码有什么问题?这是进行跨线程调用的有效方法吗? ShowDialog()有什么特别之处吗?

What's wrong with this piece of code? Isn't it a valid way to make cross-thread calls? Is there something special with ShowDialog()?

推荐答案

尝试以下方法:

private delegate void DisplayDialogCallback();

public void DisplayDialog()
{
    if (this.InvokeRequired)
    {
        this.Invoke(new DisplayDialogCallback(DisplayDialog));
    }
    else
    {
        if (this.Handle != (IntPtr)0) // you can also use: this.IsHandleCreated
        {
            this.ShowDialog();

            if (this.CanFocus)
            {
                this.Focus();
            }
        }
        else
        {
            // Handle the error
        }
    }
}

请注意InvokeRequired返回

如果控件的Handle为true，则为true 在与线程不同的线程上创建 调用线程(表明您 必须通过以下方式调用控件 调用方法)；否则为假.

true if the control's Handle was created on a different thread than the calling thread (indicating that you must make calls to the control through an invoke method); otherwise, false.

，因此，如果尚未创建控件，则返回值为false！

and therefore, if the control has not been created, the return value will be false!

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