.net 通過 HttpClient 下載文件同時報告進度的方法

通過 HttpClient 的 ContentLength 很多時候都可以拿到下載的內容的長度，通過 ReadAsync 可以返回當前讀到的長度，將讀取到的長度加起來就是已經下載的長度

看起來很簡單，於是直接給代碼

private static async Task DownloadFile(string url, FileInfo file)
{
var httpClient = new HttpClient();
var response = await httpClient.GetAsync(url);

try
{
var n = response.Content.Headers.ContentLength;
var stream = await response.Content.ReadAsStreamAsync();
using(var fileStream = file.Create())
using (stream)
{
byte[] buffer = new byte[1024];
var readLength = 0;
int length;
while ((length = await stream.ReadAsync(buffer, 0, buffer.Length)) != 0)
{
readLength += length;

Console.WriteLine("下載進度" + ((double)readLength) / n * 100);

// 寫入到文件
fileStream.Write(buffer, 0, length);
}
}

}
catch (Exception e)
{
}
}

如果不是需要獲取進度，那么最簡單的方法是

var stream = await response.Content.ReadAsStreamAsync();
using(var fileStream = file.Create())
using (stream)
{
await stream.CopyToAsync(fileStream);
}

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