一个简单的利用 WebClient 异步下载的示例（五）（完结篇）
接着上一篇，我们继续来优化。我们的 SkyParallelWebClient 可否支持切换“同步下载模式”和“异步下载模式”呢，好处是大量的代码不用改，只需要调用 skyParallelWebClient.StartAsync() 就开始异步下载，而改为 skyParallelWebClient.StartSync(); 就同步下载。如图：
同步下载：
异步下载：
1. 同步下载模式
直接贴代码了：
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
} private List<int> GetDownloadIds()
{
List<int> ids = new List<int>();
for (int i = ; i <= ; i++)
{
ids.Add(i);
}
return ids;
} private void WhenAllDownloading()
{
this.listBoxLog.Items.Insert(, string.Format("当前时间：{0}，准备开始下载...", DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss")));
//禁用按钮
EnableOrDisableButtons(false);
} private void EnableOrDisableButtons(bool enabled)
{
this.btnRunByHttpClient.Enabled = enabled;
this.btnRunByWebClient.Enabled = enabled;
} private void WhenSingleDownloading(WhenSingleDownloadEventArgs eventArg)
{
this.listBoxLog.Items.Insert(, string.Format("当前时间：{0}，剩余 {1} 个。编号 {2} 准备开始下载...", DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss"), eventArg.RemainingQueueCount, eventArg.CurrentDownloadEntry.Data));
} private void WhenSingleDownloaded(WhenSingleDownloadEventArgs eventArg)
{
this.listBoxLog.Items.Insert(, string.Format("当前时间：{0}，剩余 {1} 个。编号 {2} 下载完毕...", DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss"), eventArg.RemainingQueueCount, eventArg.CurrentDownloadEntry.Data));
} private void WhenAllDownloaded()
{
this.listBoxLog.Items.Insert(, string.Format("当前时间：{0}，下载完毕！", DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss")));
//启用按钮
EnableOrDisableButtons(true);
} private async void btnRunByHttpClient_Click(object sender, EventArgs e)
{
//SkyHttpClient skyHttpClient = new SkyHttpClient();
//try
//{
// WhenAllDownloading();
// foreach (var id in GetDownloadIds())
// {
// bool singleDownloadSuccess = await TaskDemo101.RunByHttpClient(skyHttpClient, id);
// WhenSingleDownloading(id);
// }
// WhenAllDownloaded();
//}
//catch (Exception ex)
//{
// MessageBox.Show(ex.Message, "Download Error!");
//}
} private void btnRunByWebClient_Click(object sender, EventArgs e)
{
WhenAllDownloading();
var ids = GetDownloadIds();
List<DownloadEntry> downloadConfigs = new List<DownloadEntry>();
Random rd = new Random();
foreach (var id in ids)
{
downloadConfigs.Add(new DownloadEntry(TaskDemo101.GetRandomUrl(rd), TaskDemo101.GetSavedFileFullName(), id));
}
// 方案4（同步下载，需要启动另外一个线程）
ThreadPool.QueueUserWorkItem(new WaitCallback(RunByWebClientCore), downloadConfigs);
} private void RunByWebClientCore(object state)
{
List<DownloadEntry> downloadConfigs = (List<DownloadEntry>)state;
SkyParallelWebClient skyParallelWebClient = new SkyParallelWebClient(downloadConfigs, );
skyParallelWebClient.SetMaximumForProgress += SkyParallelWebClient_SetMaximumForProgress;
skyParallelWebClient.SetRealTimeValueForProgress += SkyParallelWebClient_SetRealTimeValueForProgress;
skyParallelWebClient.WhenAllDownloaded += SkyWebClient_WhenAllDownloaded;
skyParallelWebClient.WhenSingleDownloading += SkyWebClient_WhenSingleDownloading;
skyParallelWebClient.WhenSingleDownloaded += SkyWebClient_WhenSingleDownloaded;
skyParallelWebClient.WhenDownloadingError += SkyWebClient_WhenDownloadingError;
skyParallelWebClient.StartSync();
} private void SkyParallelWebClient_SetRealTimeValueForProgress(int realTimeValue)
{
this.progressBar1.Value = realTimeValue;
} private void SkyParallelWebClient_SetMaximumForProgress(int maximum)
{
this.progressBar1.Maximum = maximum;
} private void SkyWebClient_WhenDownloadingError(Exception ex)
{
MessageBox.Show("下载时出现错误： " + ex.Message);
} private void SkyWebClient_WhenSingleDownloading(WhenSingleDownloadEventArgs eventArg)
{
WhenSingleDownloading(eventArg);
} private void SkyWebClient_WhenSingleDownloaded(WhenSingleDownloadEventArgs eventArg)
{
WhenSingleDownloaded(eventArg);
} private void SkyWebClient_WhenAllDownloaded()
{
btnRunByWebClient.Text = "用 WebClient 开始下载";
WhenAllDownloaded();
} }
运行截图：
2. 异步下载模式
直接贴代码了：
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
} private List<int> GetDownloadIds()
{
List<int> ids = new List<int>();
for (int i = ; i <= ; i++)
{
ids.Add(i);
}
return ids;
} private void WhenAllDownloading()
{
this.listBoxLog.Items.Insert(, string.Format("当前时间：{0}，准备开始下载...", DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss")));
//禁用按钮
EnableOrDisableButtons(false);
} private void EnableOrDisableButtons(bool enabled)
{
this.btnRunByHttpClient.Enabled = enabled;
this.btnRunByWebClient.Enabled = enabled;
} private void WhenSingleDownloading(WhenSingleDownloadEventArgs eventArg)
{
this.listBoxLog.Items.Insert(, string.Format("当前时间：{0}，剩余 {1} 个。编号 {2} 准备开始下载...", DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss"), eventArg.RemainingQueueCount, eventArg.CurrentDownloadEntry.Data));
} private void WhenSingleDownloaded(WhenSingleDownloadEventArgs eventArg)
{
this.listBoxLog.Items.Insert(, string.Format("当前时间：{0}，剩余 {1} 个。编号 {2} 下载完毕...", DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss"), eventArg.RemainingQueueCount, eventArg.CurrentDownloadEntry.Data));
} private void WhenAllDownloaded()
{
this.listBoxLog.Items.Insert(, string.Format("当前时间：{0}，下载完毕！", DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss")));
//启用按钮
EnableOrDisableButtons(true);
} private async void btnRunByHttpClient_Click(object sender, EventArgs e)
{
//SkyHttpClient skyHttpClient = new SkyHttpClient();
//try
//{
// WhenAllDownloading();
// foreach (var id in GetDownloadIds())
// {
// bool singleDownloadSuccess = await TaskDemo101.RunByHttpClient(skyHttpClient, id);
// WhenSingleDownloading(id);
// }
// WhenAllDownloaded();
//}
//catch (Exception ex)
//{
// MessageBox.Show(ex.Message, "Download Error!");
//}
} private void btnRunByWebClient_Click(object sender, EventArgs e)
{
WhenAllDownloading();
var ids = GetDownloadIds();
List<DownloadEntry> downloadConfigs = new List<DownloadEntry>();
Random rd = new Random();
foreach (var id in ids)
{
downloadConfigs.Add(new DownloadEntry(TaskDemo101.GetRandomUrl(rd), TaskDemo101.GetSavedFileFullName(), id));
}
//搜索： Parallel WebClient
// 方案1
//SkyWebClient skyWebClient = new SkyWebClient(downloadConfigs, this.progressBar1);
//skyWebClient.WhenAllDownloaded += SkyWebClient_WhenAllDownloaded;
//skyWebClient.WhenSingleDownloading += SkyWebClient_WhenSingleDownloading;
//skyWebClient.WhenDownloadingError += SkyWebClient_WhenDownloadingError;
//skyWebClient.Start();
// 方案2（代码已经调整，无法恢复）
//ThreadPool.QueueUserWorkItem(new WaitCallback(AsyncRunSkyParallelWebClient), downloadConfigs);
// 方案3（异步下载，完美）
SkyParallelWebClient skyParallelWebClient = new SkyParallelWebClient(downloadConfigs, );
skyParallelWebClient.SetMaximumForProgress += SkyParallelWebClient_SetMaximumForProgress;
skyParallelWebClient.SetRealTimeValueForProgress += SkyParallelWebClient_SetRealTimeValueForProgress;
skyParallelWebClient.WhenAllDownloaded += SkyWebClient_WhenAllDownloaded;
skyParallelWebClient.WhenSingleDownloading += SkyWebClient_WhenSingleDownloading;
skyParallelWebClient.WhenSingleDownloaded += SkyWebClient_WhenSingleDownloaded;
skyParallelWebClient.WhenDownloadingError += SkyWebClient_WhenDownloadingError;
skyParallelWebClient.StartSync();
// 方案4（同步下载，需要启动另外一个线程）
//ThreadPool.QueueUserWorkItem(new WaitCallback(RunByWebClientCore), downloadConfigs);
} private void RunByWebClientCore(object state)
{
List<DownloadEntry> downloadConfigs = (List<DownloadEntry>)state;
SkyParallelWebClient skyParallelWebClient = new SkyParallelWebClient(downloadConfigs, );
skyParallelWebClient.SetMaximumForProgress += SkyParallelWebClient_SetMaximumForProgress;
skyParallelWebClient.SetRealTimeValueForProgress += SkyParallelWebClient_SetRealTimeValueForProgress;
skyParallelWebClient.WhenAllDownloaded += SkyWebClient_WhenAllDownloaded;
skyParallelWebClient.WhenSingleDownloading += SkyWebClient_WhenSingleDownloading;
skyParallelWebClient.WhenSingleDownloaded += SkyWebClient_WhenSingleDownloaded;
skyParallelWebClient.WhenDownloadingError += SkyWebClient_WhenDownloadingError;
skyParallelWebClient.StartSync();
} private void SkyParallelWebClient_SetRealTimeValueForProgress(int realTimeValue)
{
this.progressBar1.Value = realTimeValue;
} private void SkyParallelWebClient_SetMaximumForProgress(int maximum)
{
this.progressBar1.Maximum = maximum;
} private void SkyWebClient_WhenDownloadingError(Exception ex)
{
MessageBox.Show("下载时出现错误： " + ex.Message);
} private void SkyWebClient_WhenSingleDownloading(WhenSingleDownloadEventArgs eventArg)
{
WhenSingleDownloading(eventArg);
} private void SkyWebClient_WhenSingleDownloaded(WhenSingleDownloadEventArgs eventArg)
{
WhenSingleDownloaded(eventArg);
} private void SkyWebClient_WhenAllDownloaded()
{
btnRunByWebClient.Text = "用 WebClient 开始下载";
WhenAllDownloaded();
} }
运行截图：
如上图：当打印了“下载完毕”后，仍然打印了许多日志，这是因为异步下载的回调是不定时的。为了避免这种情况，建议 WhenSingleDownloading 事件和 WhenSingleDownloaded 事件二选一，因为实在没有必要下载开始前和下载后都打印日志。我们再次修改代码后，得到如下图的日志。
日志是不是清晰了很多？一般下载完成，可以注册完成事件，事件里面不用打印日志，而做一些比如“修改数据库表记录的状态字段”等等。
3. 总结
SkyParallelWebClient 完整的代码如下：
/// <summary>
/// 设置进度条的最大值的事件处理
/// </summary>
/// <param name="maximum"></param>
public delegate void SetMaximumForProgressEventHandler(int maximum); /// <summary>
/// 设置进度条的当前实时的值的事件处理
/// </summary>
/// <param name="maximum"></param>
public delegate void SetRealTimeValueForProgressEventHandler(int realTimeValue); /// <summary>
/// 并行的 WebClient
/// </summary>
public class SkyParallelWebClient : SkyWebClientBase
{
ConcurrentQueue<DownloadEntry> OptionDataList = new ConcurrentQueue<DownloadEntry>(); //比如说：有 500 个元素 ConcurrentDictionary<WebClient, DownloadEntry> ProcessingTasks = new ConcurrentDictionary<WebClient, DownloadEntry>(); //当前运行中的 public event SetMaximumForProgressEventHandler SetMaximumForProgress;
protected virtual void OnSetMaximumForProgress(int maximum)
{
if (SetMaximumForProgress != null)
{
SetMaximumForProgress(maximum);
}
} public event SetRealTimeValueForProgressEventHandler SetRealTimeValueForProgress;
protected virtual void OnSetRealTimeValueForProgress(int realTimeValue)
{
if (SetRealTimeValueForProgress != null)
{
SetRealTimeValueForProgress(realTimeValue);
}
} public int ParallelCount { get; } public bool IsCompleted { get; private set; } public int Maximum { get;} private static object lockObj = new object(); /// <summary>
/// 构造函数
/// </summary>
/// <param name="downloadConfigs">要下载的全部集合，比如 N 多要下载的，N无限制</param>
public SkyParallelWebClient(IEnumerable<DownloadEntry> downloadConfigs)
:this(downloadConfigs, )
{ } /// <summary>
/// 构造函数
/// </summary>
/// <param name="downloadConfigs">要下载的全部集合，比如 N 多要下载的，N无限制</param>
/// <param name="parallelCount">单位内，并行下载的个数。切忌：该数字不能过大，否则可能很多文件因为 WebClient 超时，而导致乱文件（即：文件不完整）一般推荐 20 个左右</param>
public SkyParallelWebClient(IEnumerable<DownloadEntry> downloadConfigs, int parallelCount)
{
if (downloadConfigs == null)
{
throw new ArgumentNullException("downloadConfigs");
}
this.ParallelCount = parallelCount;
foreach (var item in downloadConfigs)
{
OptionDataList.Enqueue(item);
}
this.Maximum = OptionDataList.Count;
System.Net.ServicePointManager.DefaultConnectionLimit = int.MaxValue;
OnSetMaximumForProgress(this.Maximum);
} /// <summary>
/// 异步启动（备注：由于内部采用异步下载，所以方法不用加 Try 和返回值）
/// </summary>
public void StartAsync()
{
StartAsyncCore();
} protected void StartAsyncCore()
{
if (OptionDataList.Count <= )
{
SetIsCompletedTrue();
return;
}
while (OptionDataList.Count > && ProcessingTasks.Count <= ParallelCount)
{
DownloadEntry downloadEntry;
if (!OptionDataList.TryDequeue(out downloadEntry))
{
break;
}
DownloadFileAsync(downloadEntry);
OnWhenSingleDownloading(new WhenSingleDownloadEventArgs
{
CurrentDownloadEntry = downloadEntry,
RemainingQueueCount = OptionDataList.Count
});
}
} /// <summary>
/// 同步启动
/// </summary>
public void StartSync()
{
StartSyncCore();
} /// <summary>
/// 同步启动
/// </summary>
public void StartSync(WebClient webClient)
{
StartSyncCore(webClient);
} protected void StartSyncCore()
{
using (WebClient webClient = new WebClient())
{
StartSyncCore(webClient);
}
} protected void StartSyncCore(WebClient webClient)
{
while (OptionDataList.Count > )
{
DownloadEntry downloadEntry;
if (!OptionDataList.TryDequeue(out downloadEntry))
{
break;
}
OnWhenSingleDownloading(new WhenSingleDownloadEventArgs
{
CurrentDownloadEntry = downloadEntry,
RemainingQueueCount = OptionDataList.Count
});
DownloadFile(downloadEntry, webClient);
OnWhenSingleDownloaded(new WhenSingleDownloadEventArgs
{
CurrentDownloadEntry = downloadEntry,
RemainingQueueCount = OptionDataList.Count
});
}
SetIsCompletedTrue();
} protected void SetIsCompletedTrue()
{
if (!IsCompleted)
{
lock (lockObj)
{
if (!IsCompleted)
{
OnSetRealTimeValueForProgress();//表示已经完成
OnWhenAllDownloaded();
IsCompleted = true;
}
}
}
} private void DownloadFileAsync(DownloadEntry downloadEntry)
{
using (WebClient webClient = new WebClient())
{
webClient.Proxy = null;
webClient.DownloadFileCompleted += WebClient_DownloadFileCompleted;
webClient.DownloadFileAsync(new Uri(downloadEntry.Url), downloadEntry.Path);
ProcessingTasks.TryAdd(webClient, downloadEntry);
}
} private void DownloadFile(DownloadEntry downloadEntry)
{
using (WebClient webClient = new WebClient())
{
DownloadFile(downloadEntry, webClient);
}
} private void DownloadFile(DownloadEntry downloadEntry, WebClient webClient)
{
try
{
webClient.Proxy = null;
webClient.DownloadFile(new Uri(downloadEntry.Url), downloadEntry.Path);
}
catch (Exception ex)
{
OnWhenDownloadingError(ex);
}
} private void WebClient_DownloadFileCompleted(object sender, AsyncCompletedEventArgs e)
{
WebClient webClient = (WebClient)sender;
DownloadEntry downloadEntry;
if (ProcessingTasks.TryRemove(webClient, out downloadEntry))
{
OnWhenSingleDownloaded(new WhenSingleDownloadEventArgs
{
CurrentDownloadEntry = downloadEntry,
RemainingQueueCount = OptionDataList.Count
});
try
{
int realTimeValue = (this.Maximum - OptionDataList.Count) * / this.Maximum;
OnSetRealTimeValueForProgress(realTimeValue); //表示单个已经完成
}
catch (Exception)
{ }
}
StartAsyncCore();
}
}
谢谢浏览！
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