n 点击按钮给出 n 个输出。只需单击一次即可产生一个输出

Question

好的..所以我不知道为什么会发生这种情况。我猜我在Java中看到了类似的问题..但我不明白这些东西。我正在使用 C#，我有一个 listview，它在单击按钮时使用远程服务器更新状态进行更新。我有为此工作的代码。但是当我再次单击同一个按钮时，输出显示两次。如果我再点击一次，输出会显示三次，依此类推！！ 例如： 第一次点击：

xxx     login to server failed
yyy     login to server failed

第二次点击：

xxx     login to server failed
xxx     login to server failed
yyy     login to server failed
yyy     login to server failed

我正在使用backgroundworker，并在其中使用并行foreach 循环。我已将所有相关函数都放在这里，以便那里有所有信息。抱歉，如果这太多了！ 这是我的代码：

    private void button1_Click(object sender, EventArgs e)                        //get update button
    {
        GlobalVariables._count = 0;
        Status.statusProgress obj1 = new Status.statusProgress();
        if (getupdate_button.Text == "Stop")
        {
            backgroundWorker1.CancelAsync();
            getupdate_button.Enabled = false;
        }
        else
        {
            getupdate_button.Text = "Stop";
            listView1.Items.Clear();
            //do stuff
            backgroundWorker1.ProgressChanged += backgroundWorker1_ProgressChanged;
        }
        if (backgroundWorker1.IsBusy)
        {
            if (backgroundWorker1.CancellationPending != true)
            {
                MessageBox.Show("Please wait till the pervious operation is completed!");
            }
            else 
            {
                Complete_label.Text = "Cancelling...";
                Complete_label.Visible = true;
            }
        }
        else
        {
            backgroundWorker1.RunWorkerAsync(obj1);                                //calling background worker
        }
    }

工作：

    private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)                         //the boss-- the background worker
    {
        System.ComponentModel.BackgroundWorker worker;
        worker = (System.ComponentModel.BackgroundWorker)sender;
        Status obj1 = new Status();
        Status.statusProgress obj = new Status.statusProgress();

        if ((backgroundWorker1.CancellationPending == true))
        {
            e.Cancel = true;
        }
        else
        {
            obj1.Calculation(worker, e);
        }
        e.Result = obj;
    }

计算方法：

    public void Calculation(System.ComponentModel.BackgroundWorker worker, System.ComponentModel.DoWorkEventArgs e)
    {
        Status.statusProgress obj = (Status.statusProgress)e.Argument;
        //stuff

            var file = File.ReadAllLines(obj.SourceFile);

            List<string> namelist = null;
            namelist = new List<string>(file);
            Parallel.ForEach(namelist, /*new ParallelOptions { MaxDegreeOfParallelism = 4 }, */line =>
            //foreach (string line in namelist)
            {
                var progress = new statusProgress();
                progress.TotalSysCount = obj.TotalSysCount;
                Status.statusProgress result = new Status.statusProgress();
                if (worker.CancellationPending)
                {
                    e.Cancel = true;
                    worker.ReportProgress(result.SysCount, result);
                }
                else
                {
                    //this.SystemName = line;//file.ReadLine();                        
                    progress.SystemName = line;
                    //result = progress;
                    result = OneSystem(line);
                    //work with result
        }
                count1 = Interlocked.Increment(ref count);
                //stuff
                worker.ReportProgress(count1, progress);
                Thread.Sleep(200);

             });

        }
    }

报告进度方法：

     private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {
    try
                {
                    var newItem = listView1.Items.Add("");
                    newItem.SubItems.Add(result.SystemName);
                    newItem.SubItems.Add(result.StatusString);
                    newItem.SubItems.Add(result.AvailableUpdatesCount.ToString());
                }
                catch (Exception ex)
                {}

            update_text(result);
            progressBar1.Maximum = 100;
            int perc = (int)((result.SysCount * 100) / result.TotalSysCount);
            progressBar1.Value = perc;
            Complete_label.Text = perc.ToString()+"%";
            if (progressBar1.Value == 100)
            {
                Complete_label.Text = "Complete!";
                getupdate_button.Enabled = false;
            }
    }

Answer 1

我猜问题出在这里：

backgroundWorker1.ProgressChanged += backgroundWorker1_ProgressChanged;

如果您每次执行整个单击 操作时都添加一个ProgressChanged 事件处理程序，那么在每次单击后，您将增加事件被处理的次数。

归根结底，您应该在某些应用程序的初始化代码或类构造函数中添加事件处理程序，而不是在单击事件处理程序中这样做。也就是说，您将确保在每个应用程序生命周期中添加一次 backgroundWorker1_ProgressChanged 事件处理程序。