Question

尝试设置我在后台运行BackgroundWorker的设置，然后在完成每个步骤时在单独的模式对话框中更新其进度。当然，问题是尝试从BackgroundWorker线程更新进度对话框会导致跨线程问题。

代码:(有问题的行包含用***包围的注释）

public void StartProcess()
{
    // dialog that shows a simple marquee progress bar and a message
    ProgressDialog progress = new ProgressDialog("Starting operation...");

    // create background worker thread
    BackgroundWorker bw = new BackgroundWorker();
    bw.WorkerSupportsCancellation = true;
    bw.WorkerReportsProgress = true;
    bw.DoWork += Bw_DoWork;
    bw.RunWorkerCompleted += Bw_RunWorkerCompleted;

    if(!bw.IsBusy)
    {
        bw.RunWorkerAsync();
        progress.ShowDialog();
    }
}

private void Bw_DoWork(object sender, DoWorkEventArgs e)
{
    BackgroundWorker bw = sender as BackgroundWorker;
    if(bw.CancellationPending)
    {
        e.Cancel = true;
    }
    else
    {
        // perform step 1

        // *** this line generates cross-thread problems ***
        progress.Message = "Performing step 2...";

        // etc...
    }
}

这是进度对话框的代码：

public partial class ProgressDialog : Form
{
    public string Message
    {
        get
        {
            return lblMessage.Text;
        }
        set
        {
            if(lblMessage.InvokeRequired)
            {
                // *** not sure how to invoke this by passing the "value" parameter ***
                // *** returns a TargetParameterCountException ***
                // *** trying to pass "value" in results in "Method name expected" error ***
                lblMessage.Invoke(new UpdateMessageDelegate(SetMessage));
            }
        }
    }

    private delegate void UpdateMessageDelegate(string s);

    private void SetMessage(string s)
    {
        lblMessage.Text = s;
    }
}

如何使用set方法和隐式value参数安全地更改标签的文本值？

Answer 1

尝试以这种方式调用它：

lblMessage.Invoke((Action)(() => SetMessage(value)));

然后您还可以避免创建私有UpdateMessageDelegate委托。

Answer 2

找到了一种方法：

table tr:first-child {
  font-weight: bold;
}

@media (min-width: 300px) {
  table {
    display: inline-block;
  }
}

使用参数调用委托方法名称

2 个答案: