在Winforms（C＃）中使用帶有MVP模式的backgroundworker

Question

我一直試圖通過使用MVP模式來重構應用程序的意大利面條代碼。 但現在我正在努力解決這個問題：

具有調用DoWork方法（后台工作者）的按鈕的表單，該方法是長操作。 我的問題是，如果我將長操作從視圖移到Presenter，那么如何將進度更改從此操作發送到View？ BGW也必須在演示者中嗎？ 你能給我一個如何做到這一點的樣本嗎？

先感謝您。

Answer 1

這概述了BackgroundWorker的用法：

private BackgroundWorker _backgroundWorker;

public void Setup( )
{
    _backgroundWorker = new BackgroundWorker();
    _backgroundWorker.WorkerReportsProgress = true;
    _backgroundWorker.DoWork +=
      new DoWorkEventHandler(BackgroundWorker_DoWork);
    _backgroundWorker.ProgressChanged +=
      new ProgressChangedEventHandler(BackgroundWorker_ProgressChanged);
    _backgroundWorker.RunWorkerCompleted +=
      new RunWorkerCompletedEventHandler(BackgroundWorker_RunWorkerCompleted);

    // Start the BackgroundWorker
    _backgroundWorker.RunWorkerAsync();
}

void BackgroundWorker_DoWork(object sender, DoWorkEventArgs e)
{
    // This method runs in a background thread. Do not access the UI here!
    while (work not done) {
        // Do your background work here!

        // Send messages to the UI:
        _backgroundWorker.ReportProgress(percentage_done, user_state);
        // You don't need to calculate the percentage number if you don't
        // need it in BackgroundWorker_ProgressChanged.
    }
    // You can set e.Result = to some result;
}

void BackgroundWorker_ProgressChanged(object sender,
                                      ProgressChangedEventArgs e)
{
    // This method runs in the UI thread and receives messages from the backgroud thread.

    // Report progress using the value e.ProgressPercentage and e.UserState
}

void BackgroundWorker_RunWorkerCompleted(object sender,
                                         RunWorkerCompletedEventArgs e)
{
    // This method runs in the UI thread.
    // Work is finished! You can display the work done by using e.Result
}

---

UPDATE

這個BackgroundWorker必須成為事業的主持人。 像MVP，MVC或MVVM這樣的模式的想法是從視圖中刪除盡可能多的代碼。 該視圖只具有非常特定於視圖本身的代碼，例如在Paint事件處理程序中創建視圖或繪圖等。 視圖中的另一種代碼是與演示者或控制器通信所需的代碼。 然而，呈現邏輯必須在演示者中。

您將使用在UI線程中運行的BackgroundWorker_ProgressChanged方法將更改發送到視圖。 通過調用視圖的公共方法或通過設置視圖的公共屬性或通過公開公共屬性，視圖可以通過將其屬性或其控件的屬性綁定到它來附加到該屬性。 （這是從MVVM模式中借用的。）如果您決定將視圖綁定到演示者的屬性，則演示者必須實現INotifyPropertyChanged以通知視圖屬性已更改。

注意 ：不允許除UI線程之外的另一個線程直接與視圖交互（如果您嘗試這樣做，則拋出異常）。 因此，BackgroundWorker_DoWork無法直接與視圖交互，因此調用ReportProgress，后者又在UI線程中運行BackgroundWorker_ProgressChanged。

Answer 2

您可以將BackGroundWorker放置在演示者中，並向視圖添加方法以顯示進度。 像這樣的東西：

//Add a method to your view interface to show progress if you need it.
public interface IView
{
     void ShowProgress(int progressPercentage);
}
//Implement method in the view.
public class MyView : Form, IView
{
    public MyView()
    {
        //Assume you have added a ProgressBar to the form in designer.
        InitializeComponent();
    }

    public void ShowProgress(int progressPercentage)
    {
        //Make it thread safe.

        if (progressBar1.InvokeRequired)
            progressBar1.Invoke(new MethodInvoker(delegate { progressBar1.Value = progressPercentage; }));
        else
            progressBar1.Value = progressPercentage;
    }
}

// In your presenter class create a BackgroundWorker and handle it's do work event and put your time consuming method there.
public class MyPresenter
{
    private BackgroundWorker _bw;

    public MyPresenter()
    {
        _bw = new BackgroundWorker();
        _bw.WorkerReportsProgress = true;
        _bw.DoWork += new DoWorkEventHandler(_bw_DoWork);
    }

    private void _bw_DoWork(object sender, DoWorkEventArgs e)
    {
        //Time consuming operation
        while (!finished)
        {
            //Do the job
            _bw.ReportProgress(jobProgressPercentage);

        }
    }

    public void StartTimeConsumingJob()
    {
        _bw.RunWorkerAsync();
    }
}

完成后不要忘記處理BackgroundWorker。

Answer 3

根據您的意見，我設法解決了這個問題。 請評論您使用此方法可能發現的任何缺陷：

*查看界面*

public interface IView
{
   void ShowProgress( int progressPercentage);
}

*查看（表格）*

public partial class Form1 : Form, IView
    {
        MyPresenter p ;

        public Form1()
        {
            InitializeComponent();
            p = new MyPresenter(this);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (p.IsBusy())
            {
                return;
            }
            p.StartTimeConsumingJob();
        }

        public void ShowProgress(int progressPercentage)
        {
            if (progressBar1.InvokeRequired)
                progressBar1.Invoke(new MethodInvoker(delegate { progressBar1.Value = progressPercentage; }));
            else
                progressBar1.Value = progressPercentage;
        }

        private void button2_Click(object sender, EventArgs e)
        {
            p.Cancel();
        }

    }

* 主持人 *

public class MyPresenter
{
    private BackgroundWorker _bw;
    private IView _view;

    public MyPresenter(IView Iview)
    {
        _view = Iview;
        _bw = new BackgroundWorker();
        _bw.WorkerReportsProgress = true;
        _bw.WorkerSupportsCancellation = true;
        _bw.DoWork += new DoWorkEventHandler(_bw_DoWork);
        _bw.ProgressChanged += new ProgressChangedEventHandler(_bw_ProgressChanged);
        _bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(_bw_Completed);
    }

    public void StartTimeConsumingJob()
    {
        _bw.RunWorkerAsync();
    }

    private void _bw_DoWork(object sender, DoWorkEventArgs e)
    {
        //Time consuming operation Do the job
        Thread.Sleep(1000);
        _bw.ReportProgress(50);
        Thread.Sleep(2000);
        if(_bw.CancellationPending)
        {
            e.Result = false;
        }
    }

    public bool IsBusy()
    {
        return _bw.IsBusy;
    }

    public void Cancel()
    {
        _bw.CancelAsync();
    }

    private void _bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {
        _view.ShowProgress(e.ProgressPercentage);
    }

    private void _bw_Completed(object sender, RunWorkerCompletedEventArgs e)
    {
        if((bool)e.Result)
        _view.ShowProgress(100);
        else
            _view.ShowProgress(0);

        _bw.Dispose();
    }
}