我做了一个缓存图像的项目。我想在主线程中等待完整的 DownloadImage 函数，然后返回保存的位图。那可能吗？我做得对吗？
public static ImageSource GetImage(int id)
{
BitmapImage bitmap = new BitmapImage();
String fileName=string.Format("ImageCache/{0}.jpg", id);
using (IsolatedStorageFile myIsolatedStorage = IsolatedStorageFile.GetUserStoreForApplication())
{
if (!myIsolatedStorage.DirectoryExists("ImageCache"))
{
myIsolatedStorage.CreateDirectory("ImageCache");
}
if (myIsolatedStorage.FileExists(fileName))
{
using (IsolatedStorageFileStream fileStream = myIsolatedStorage.OpenFile(fileName, FileMode.Open, FileAccess.Read))
{
bitmap.SetSource(fileStream);
}
}
else
{
DownloadImage(id);
//HERE - how to wait for end of DownloadImage and then do that below??
using (IsolatedStorageFileStream fileStream = myIsolatedStorage.OpenFile(fileName, FileMode.Open, FileAccess.Read))
{
bitmap.SetSource(fileStream);
}
}
}
return bitmap;
}
这是下载图像功能：
private static void DownloadImage(Object id)
{
WebClient client = new WebClient();
client.OpenReadCompleted += new OpenReadCompletedEventHandler(client_OpenReadCompleted);
client.OpenReadAsync(new Uri(string.Format("http://example.com/{0}.jpg", id)), id);
}
private static void client_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e)
{
using (IsolatedStorageFile myIsolatedStorage = IsolatedStorageFile.GetUserStoreForApplication())
{
if (e.Error == null && !e.Cancelled)
{
try
{
string fileName = string.Format("ImageCache/{0}.jpg", e.UserState);
IsolatedStorageFileStream fileStream = myIsolatedStorage.CreateFile(fileName);
BitmapImage image = new BitmapImage();
image.SetSource(e.Result);
WriteableBitmap wb = new WriteableBitmap(image);
// Encode WriteableBitmap object to a JPEG stream.
Extensions.SaveJpeg(wb, fileStream, wb.PixelWidth, wb.PixelHeight, 0, 85);
fileStream.Close();
}
catch (Exception ex)
{
//Exception handle appropriately for your app
}
}
}
}