如何在事件之外使用事件参数

Question

我正在尝试创建自定义下载应用。除了无法从“DownloadProgressChangedEventArgs”中获取“percent1”变量的下载所有按钮之外，它都可以正常工作。我已经在 mainForm 构造函数之前实例化了它，但它不会读取更改的值。

这是代码，由于大部分与问题无关，因此被部分剥离：

public partial class Main : Form
{
//Variables (not all, just the one im having issues with)
    private double percentage1;

//Main form constructor
    public Main(){...}

//Download File Async custom method
    public void DldFile(string url, string fileName, string localPath, AsyncCompletedEventHandler completedName, DownloadProgressChangedEventHandler progressName)
    {
            WebClient webClient = new WebClient();
            webClient.DownloadFileAsync(new Uri(url), localPath + "\\" + fileName);
            webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(completedName);
            webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(progressName);
    }

//Button 1 click event to start download
    private void btnDld1_Click(object sender, EventArgs e)
    {
        if (url1 != "" && Directory.Exists(localPath1))
        {
            _startDate1 = DateTime.Now;
            DldFile(url1, fileName1, localPath1, completed1, progress1);
        }
        //took out the try/catch, other ifs to try and cut it down
    }

//Download Progress Changed event for Download 1
    public void progress1(object sender, DownloadProgressChangedEventArgs e)
    {
        percentage1 = e.ProgressPercentage; //THIS IS WHERE I WAS EXPECTING TO UPDATE "percentage1"
        progressBar1.Value = int.Parse(Math.Truncate(percentage1).ToString());
    }

//Button that starts all downloads click event where all my problems are at the moment
    private void btnDldAll_Click(object sender, EventArgs e)
    {
        //The progress bar that should let me know the global status for all webClients
        progressBarAll.Value = (
            int.Parse(Math.Truncate(percentage1).ToString()) + //HERE IS MY PROBLEM
            int.Parse(Math.Truncate(percentage2).ToString()) + //HERE IS MY PROBLEM
            int.Parse(Math.Truncate(percentage3).ToString()) + //HERE IS MY PROBLEM
            int.Parse(Math.Truncate(percentage4).ToString()) + //HERE IS MY PROBLEM
            int.Parse(Math.Truncate(percentage5).ToString())) / 5; //HERE IS MY PROBLEM

        //Checks if the link exists and starts it from the download button click event
        if (url1 != "")
        {
            btnDld1.PerformClick();
        }
        //Continues for url2, 3, 4, 5 and else
    }
}

所以这是我找到的让你知道我想要完成什么的最短方法，如果有什么遗漏请告诉我，我会尽快添加任何信息。

我试图实例化“progress1”来尝试访问它的百分比1 变量，但它没有工作。我试过用 webClient 做同样的事情，但也没有用。我使用谷歌和堆栈流搜索无济于事。所以我不确定这个问题是否太愚蠢，或者有一种不同的方式来看待这个完全超出我的思维方式的问题。

所以主要问题是更新“percentage1”变量并使用它。 当我掌握正确的值时，还有其他关于“progressBarAll.Value”计算的问题将得到解决。因此，如果您看到它，则无需担心。

Answer 1

尽量不要考虑“在事件之外使用事件参数”。考虑更新表单的状态。

使用属性简化更新逻辑：

public partial class Main : Form
{
  private double percentage1;
  private double percentage2;
  private double percentage3;
  private double percentage4;
  private double percentage5;

  private double Percentage1 
  {
    get
    {
      return this.percentage1;
    }
    set
    {
      this.percentage1 = value;
      this.UpdatePercentageAll();  // this will update overall progress whenever the first one changes

      progressBar1.Value = GetValueFromPercentage(value);
    }
  }
  private double Percentage2
  // same code as for Percentage1

  void UpdatePercentageAll()
  {
    this.PercentageAll = (this.Percentage1 + this.Percentage2 + this.Percentage3 + this.Percentage4 + this.Percentage5) / 5;
  }

  static int GetValueFromPercentage(double percentage)
  {
    return (int)Math.Truncate(percentage);
  }

  double percentageAll;
  private double PercentageAll
  {
    get
    {
      return this.percentageAll;
    }
    set
    {
      this.percentageAll = value;

      progressBarAll.Value = GetValueFromPercentage(value);
    }
  }

  //Download File Async custom method
  public void DldFile(string url, string fileName, string localPath, AsyncCompletedEventHandler completedName, DownloadProgressChangedEventHandler progressName)
  {
    WebClient webClient = new WebClient();
    webClient.DownloadFileAsync(new Uri(url), localPath + "\\" + fileName);
    webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(completedName);
    webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(progressName);
  }

  //Button 1 click event to start download
  private void btnDld1_Click(object sender, EventArgs e)
  {
    if (url1 != "" && Directory.Exists(localPath1))
    {
        this.StartDownloadFile1();
    }
    //took out the try/catch, other ifs to try and cut it down
  }
  void StartDownloadFile1()
  {
        this.Percentage1 = 0;
        _startDate1 = DateTime.Now;
        DldFile(url1, fileName1, localPath1, completed1, progress1);
  }
  //Download Progress Changed event for Download 1
  public void progress1(object sender, DownloadProgressChangedEventArgs e)
  {
    this.Percentage1 = e.ProgressPercentage; // update property, not field

    //this will be done in property setters
    //progressBar1.Value = int.Parse(Math.Truncate(percentage1).ToString());
  }
  // then add similar code for other download buttons

  //Button that starts all downloads click event where all my problems are at the moment
  private void btnDldAll_Click(object sender, EventArgs e)
  {
    //Checks if the link exists and starts it from the download button click event
    if (url1 != "")
    {
        this.StartDownloadFile1();
    }
    //Continues for url2, 3, 4, 5 and else
  }
}

我会进一步重构代码，但我认为如果代码更接近原始代码，您会更容易理解。

主要思想是创建一组像数学函数一样工作的链接属性。在编写PercentageX 属性时，我有点说'让PercentageAll 成为所有百分比的平均值'。然后我有每个下载更新它自己的进度。一旦更新了任何进度，它就会更新平均值，我不必在进度更改事件处理程序中记住。

最后一点是从百分比属性更新进度条。这很简单：一旦更改百分比，我需要更新一个条形图。如果是这样，为什么还要写类似的东西

this.Percentage1 = x;
this.progressBar1.Value = (int)Math.Truncate(x);

在这种情况下，我必须记住，一旦我更改了Percentage1，我就必须更新栏。在我的例子中，我只是为只在一个地方并且每次都有效的东西创建了一个严格的规则。所以我就是不能忘记它。如果我需要改变规则，我只需要改变一个地方，所以我不能再犯错误了。

我演示的技术可以表达为一个众所周知的规则：“一个规则 - 一个位置”，这意味着您应该尝试在代码中只使用一个位置来表达程序中存在的每个逻辑规则。这是一个很重要的思想，建议大家学习使用。