wp7 利用ZipOutputStream压缩.txt文件问题

//压缩
private static void CreateZipFile(string filesPath, string zipFilePath)
{
using (IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication())
{
if (isf.FileExists(filesPath))//判断文件夹是否存在
{
MessageBox.Show("文件夹不存在");
}
}
using (IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication())
{
if (isf.DirectoryExists(Used.strSignInPath))//判断文件是否存在
{
MessageBox.Show("文件不存在");
return;
}
string[] filenames = isf.GetFileNames(filesPath);
try
{
using (ZipOutputStream s = new ZipOutputStream(isf.CreateFile(zipFilePath)))
{
s.SetLevel(9);
byte[] buffer = new byte[4096];
foreach (string file in filenames)
{
ZipEntry entry = new ZipEntry(file);
entry.DateTime = DateTime.Now;
s.PutNextEntry(entry);
using (FileStream fs = File.OpenRead(file))
{
int sourceBytes;
do
{
sourceBytes = fs.Read(buffer, 0, buffer.Length);
s.Write(buffer, 0, sourceBytes);
} while (sourceBytes > 0);
}
}
s.Finish();
s.Close();
}
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
}
}
}
文件夹和.txt文件都是用IsolatedStorageFile创建的为什么压缩不成功呢？