在我的应用程序可以从网上下载一些媒体文件。 通常我用WebClient.OpenReadCompleted方法下载，解密和保存文件到IsolatedStorage。 它运作良好，并期待这样的：
private void downloadedSong_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e, SomeOtherValues someOtherValues) // delegate, uses additional values
{
// Some preparations
try
{
if (e.Result != null)
{
using (isolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication())
{
// working with the gained stream, decryption
// saving the decrypted file to isolatedStorage
isolatedStorageFileStream = new IsolatedStorageFileStream("SomeFileNameHere", FileMode.OpenOrCreate, isolatedStorageFile);
// and use it for MediaElement
mediaElement.SetSource(isolatedStorageFileStream);
mediaElement.Position = new TimeSpan(0);
mediaElement.MediaOpened += new RoutedEventHandler(mediaFile_MediaOpened);
// and some other work
}
}
}
catch(Exception ex)
{
// try/catch stuff
}
}
但经过一番调查，我发现，与大文件（对我来说这是超过100 MB）下载此文件中我得到了OutOfMemory例外。 我想这是因为WebClient.OpenReadCompleted加载整个流进RAM和扼流圈......我需要更多的内存来解密此流。
又经过调查，我发现了如何在这个文件保存到IsolatedStorage（或解密，然后在我的OCASION保存）将大型文件分成OpenReadCompleted事件之后块，但这仅仅的问题......主要部分帮助问题是如何防止在下载过程中手机扼流圈 。 有没有一种方法来下载大文件的块？ 然后，我可以用找到的解决方案，通过解密过程。 （和仍然我需要找到一种方式来加载这么大的文件到MediaElement的，但是这将是另一个问题）
回答：
private WebHeaderCollection headers;
private int iterator = 0;
private int delta = 1048576;
private string savedFile = "testFile.mp3";
// some preparations
// Start downloading first piece
using (IsolatedStorageFile isolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication())
{
if (isolatedStorageFile.FileExists(savedFile))
isolatedStorageFile.DeleteFile(savedFile);
}
headers = new WebHeaderCollection();
headers[HttpRequestHeader.Range] = "bytes=" + iterator.ToString() + '-' + (iterator + delta).ToString();
webClientReadCompleted = new WebClient();
webClientReadCompleted.Headers = headers;
webClientReadCompleted.OpenReadCompleted += downloadedSong_OpenReadCompleted;
webClientReadCompleted.OpenReadAsync(new Uri(song.Link));
// song.Link was given earlier
private void downloadedSong_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e)
{
try
{
if (e.Cancelled == false)
{
if (e.Result != null)
{
((WebClient)sender).OpenReadCompleted -= downloadedSong_OpenReadCompleted;
using (IsolatedStorageFile myIsolatedStorage = IsolatedStorageFile.GetUserStoreForApplication())
{
using (IsolatedStorageFileStream fileStream = new IsolatedStorageFileStream(savedFile, FileMode.Append, FileAccess.Write, myIsolatedStorage))
{
int mediaFileLength = (int)e.Result.Length;
byte[] byteFile = new byte[mediaFileLength];
e.Result.Read(byteFile, 0, byteFile.Length);
fileStream.Write(byteFile, 0, byteFile.Length);
// If there's something left, download it recursively
if (byteFile.Length > delta)
{
iterator = iterator + delta + 1;
headers = new WebHeaderCollection();
headers[HttpRequestHeader.Range] = "bytes=" + iterator.ToString() + '-' + (iterator + delta).ToString();
webClientReadCompleted.Headers = headers;
webClientReadCompleted.OpenReadCompleted += downloadedSong_OpenReadCompleted;
webClientReadCompleted.OpenReadAsync(new Uri(song.Link));
}
}
}
}
}
}
