[c#]WebClient异步下载文件并显示进度

摘要

一个例子

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Wolfy.DownLoad
{
public partial class MainFrm : Form
{
private string _saveDir;
public MainFrm()
{
InitializeComponent();
_saveDir = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "download");
}

private void MainFrm_Load(object sender, EventArgs e)
{

if (!Directory.Exists(_saveDir))
{
Directory.CreateDirectory(_saveDir);
}

}

private void btnDownLoad_Click(object sender, EventArgs e)
{
string imageUrl = "http://image.3761.com/nvxing/2016022921/2016022921382152113.jpg";

string fileExt = Path.GetExtension(imageUrl);
string fileNewName = Guid.NewGuid() + fileExt;
bool isDownLoad = false;
string filePath = Path.Combine(_saveDir, fileNewName);
if (File.Exists(filePath))
{
isDownLoad = true;
}
var file = new FileMessage
{
FileName = fileNewName,
RelativeUrl = "nvxing/2016022921/2016022921382152113.jpg",
Url = imageUrl,
IsDownLoad = isDownLoad,
SavePath = filePath
};

if (!file.IsDownLoad)
{

string fileDirPath = Path.GetDirectoryName(file.SavePath);
if (!Directory.Exists(fileDirPath))
{
Directory.CreateDirectory(fileDirPath);
}
try
{
WebClient client = new WebClient();
client.DownloadFileCompleted += client_DownloadFileCompleted;
client.DownloadProgressChanged += client_DownloadProgressChanged;
client.DownloadFileAsync(new Uri(file.Url), file.SavePath, file.FileName);
}
catch
{

}

}
}
void client_DownloadFileCompleted(object sender, AsyncCompletedEventArgs e)
{
if (e.UserState != null)
{
this.lblMessage.Text = e.UserState.ToString() + ",下载完成";
}
}

void client_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
{
this.proBarDownLoad.Minimum = 0;
this.proBarDownLoad.Maximum = (int)e.TotalBytesToReceive;
this.proBarDownLoad.Value = (int)e.BytesReceived;
this.lblPercent.Text = e.ProgressPercentage + "%";
}
}
}