跨线程操作在 BackgroundWorker 中无效

Question

我想在数据网格视图中显示一些有关表单加载的数据，我想显示的数据是大量行，当我使用后台工作处理器时，它会显示以下错误。

我的代码：

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
    try
    {
        FTPUtility obj = new FTPUtility();
        dataGridViewRequest.DataSource = obj.ListRequestFiles();
        dataGridViewRequest.Columns[0].AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill;
        dataGridViewRequest.Columns[1].AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill;
        dataGridViewRequest.Columns[2].AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill;

        dataGridViewResponses.DataSource = obj.ListResponseFiles();
        dataGridViewResponses.Columns[0].AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill;
        dataGridViewResponses.Columns[1].AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill;
        dataGridViewResponses.Columns[2].AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill;

    }
    catch (Exception ex)
    {

        MessageBox.Show(ex.Message, "Error Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
    }
}

表单加载：

private void FormFTP_Load(object sender, EventArgs e)
{
    try
    {

        //this.comboBoxRequests.SelectedIndex = 0;
        backgroundWorker1.RunWorkerAsync();

    }
    catch (Exception ex)
    {

        MessageBox.Show(ex.Message, "Error Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
    }
}

Answer 1

有许多不同的方法可以防止表单被冻结。
例如，您可以像这样加载数据：

private async void Form_Load(object sender, EventArgs e)
{
    //do some initializations
    await LoadData();
    //do some other initializations that you need to perform.
}

private async Task LoadData()
{
    //Load your data here
    //For example
    FTPUtility obj = new FTPUtility();
    dataGridViewRequest.DataSource = obj.ListRequestFiles();
}

这样在运行表单时，命令在 UI 响应时按照您编写的顺序运行，您将不会遇到使用BackgroundWorker 或跨线程操作异常等线程的常见困难。

关键在于使用 async/await。更多信息请阅读Asynchronous Programming with Async and Await

记住这种方式，每一个你想调用LoadData的地方，都应该这样调用：

await LoadData();

你写这段代码的方法应该是异步的：

private async void RefreshButton_Click(object sender, EventArgs e)
{
    await LoadData();
}

为 .Net 4.0 编辑

---

对于 .Net 4.0，您可以同时使用 Task.Run 或 BackgroundWorker。我推荐Task.Run，因为它更简单，更易读。

请注意，当您从 UI 以外的其他线程访问 UI 元素时，将引发跨线程操作异常。在这种情况下，您应该改用this.Invoke(new Action(()=>{/*Access UI Here*/}));。并且永远不要在你的调用部分中放置一个耗时的任务。

BackgroundWorker 方法：

private void Form1_Load(object sender, EventArgs e)
{
    backgroundWorker1.RunWorkerAsync();
    //If you put some code here for example MessageBox.Show(""); 
    //The code will immadiately run and don't wait for worker to complete the task.
}

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
    this.LoadData();
}

public void LoadData()
{
    var ftp = new FtpUtility();
    var data = ftp.ListRequestFiles();
    this.Invoke(new Action(() =>
    {
        //Setup columns and other UI stuff
        //Set datasource of grid
        this.dataGridView1.DataSource = data;
    }));
}

• 记住你以前使用LoadData的所有地方，现在你应该改用backgroundWorker1.RunWorkerAsync();。
• 如果你想在工人完成任务后做一份工作，请将你的工作放在backgroundWorker1_RunWorkerCompleted 或Invoke 的LoadData 的一部分。

Task.Run 方法

private void Form1_Load(object sender, EventArgs e)
{
    Task.Run(() =>
    {
        LoadData();
    })
    .ContinueWith(x =>
    {
        //You can put codes you want run after LoadData completed here
        //If you access the UI here, you should use Invoke
    });
    //If you put some code here for example MessageBox.Show(""); 
    //The code will immadiately run and don't wait for worker to complete the task.
}

public void LoadData()
{
    var ftp = new FtpUtility();
    var data = ftp.ListRequestFiles();
    this.Invoke(new Action(() =>
    {
        //Setup columns and other UI stuff
        //Set datasource of grid
        this.dataGridView1.DataSource = data;
    }));
}

• 记住你以前使用LoadData的所有地方，现在你应该改用Task.Run(()=>{LoadData();});。
• 如果您想在LoadData 完成后做一份工作，请将您的工作放入ContinueWith 或Invoke 的LoadData 的一部分。

Answer 2

试试这个。

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
    try
    {

       dataGridViewRequest.Invoke(new Action(() => {
            FTPUtility obj = new FTPUtility();
            dataGridViewRequest.DataSource = obj.ListRequestFiles();
            dataGridViewRequest.Columns[0].AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill;
            dataGridViewRequest.Columns[1].AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill;
            dataGridViewRequest.Columns[2].AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill;

            dataGridViewResponses.DataSource = obj.ListResponseFiles();
            dataGridViewResponses.Columns[0].AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill;
            dataGridViewResponses.Columns[1].AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill;
            dataGridViewResponses.Columns[2].AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill;
       }));
    }
    catch (Exception ex)
    {

        MessageBox.Show(ex.Message, "Error Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
    }
}

private void FormFTP_Load(object sender, EventArgs e)
{
    try
    {

        //this.comboBoxRequests.SelectedIndex = 0;
        backgroundWorker1.RunWorkerAsync();

    }
    catch (Exception ex)
    {

        MessageBox.Show(ex.Message, "Error Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
    }
}