c# - BindingSource 和跨线程异常

Question

为了解释这个问题，我把所有需要的东西都放到了一个小的示例应用程序中，希望能解释这个问题。我真的试图尽可能减少所有内容，但在我的实际应用程序中，这些不同的 Actor 彼此不认识，也不应该。因此，像“在上面几行中获取变量并对其调用 Invoke”这样的简单回答是行不通的。

让我们从代码开始，然后再进行更多解释。首先有一个实现 INotifyPropertyChanged 的​​简单类:

public class MyData : INotifyPropertyChanged
{
    private string _MyText;

    public MyData()
    {
        _MyText = "Initial";
    }

    public string MyText
    {
        get { return _MyText; }

        set
        {
            _MyText = value;
            PropertyChanged(this, new PropertyChangedEventArgs("MyText"));
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

所以没什么特别的。这里的示例代码可以简单地放入任何空的控制台应用程序项目中:

static void Main(string[] args)
{
    // Initialize the data and bindingSource
    var myData = new MyData();
    var bindingSource = new BindingSource();
    bindingSource.DataSource = myData;

    // Initialize the form and the controls of it ...
    var form = new Form();

    // ... the TextBox including data bind to it
    var textBox = new TextBox();
    textBox.DataBindings.Add("Text", bindingSource, "MyText");
    textBox.DataBindings.DefaultDataSourceUpdateMode = DataSourceUpdateMode.OnPropertyChanged;
    textBox.Dock = DockStyle.Top;
    form.Controls.Add(textBox);

    // ... the button and what happens on a click
    var button = new Button();
    button.Text = "Click me";
    button.Dock = DockStyle.Top;
    form.Controls.Add(button);

    button.Click += (_, __) =>
    {
        // Create another thread that does something with the data object
        var worker = new BackgroundWorker();

        worker.RunWorkerCompleted += (___, ____) => button.Enabled = true;
        worker.DoWork += (___, _____) =>
        {
            for (int i = 0; i < 10; i++)
            {
                // This leads to a cross-thread exception
                // but all i'm doing is simply act on a property in
                // my data and i can't see here that any gui is involved.
                myData.MyText = "Try " + i;
            }
        };

        button.Enabled = false;
        worker.RunWorkerAsync();
    };

    form.ShowDialog();
}

如果您要运行此代码，您将通过尝试更改 MyText 属性得到一个跨线程异常。这会导致 MyData 对象调用 PropertyChanged，这将被 BindindSource 捕获。然后，这将根据 Binding，尝试更新 TextBox 的 Text 属性。这显然会导致异常。

我最大的问题是 MyData 对象不应该知道有关 gui 的任何信息(因为它是一个简单 数据对象)。此外，工作线程对图形用户界面一无所知。它只是作用于一堆数据对象并对其进行操作。

恕我直言，我认为 BindingSource 应该检查接收对象在哪个线程上，并执行适当的 Invoke() 以获得它们的值。不幸的是，这不是内置的(或者我错了吗？)，所以我的问题是:

如果数据对象或工作线程都知道正在监听其事件以将数据推送到 gui 中的绑定(bind)源，如何解决此跨线程异常。

Answer 1

下面是上面例子中解决这个问题的部分:

button.Click += (_, __) =>
{
    // Create another thread that does something with the data object
    var worker = new BackgroundWorker();

    worker.DoWork += (___, _____) =>
    {
        for (int i = 0; i < 10; i++)
        {
            // This doesn't lead to any cross-thread exception
            // anymore, cause the binding source was told to
            // be quiet. When we're finished and back in the
            // gui thread tell her to fire again its events.
            myData.MyText = "Try " + i;
        }
    };

    worker.RunWorkerCompleted += (___, ____) =>
    {
        // Back in gui thread let the binding source
        // update the gui elements.
        bindingSource.ResumeBinding();
        button.Enabled = true;
    };

    // Stop the binding source from propagating
    // any events to the gui thread.
    bindingSource.SuspendBinding();
    button.Enabled = false;
    worker.RunWorkerAsync();
};

所以这不会再导致任何跨线程异常。此解决方案的缺点是您不会在文本框中显示任何中间结果，但总比没有好。