我刚开始接触多线程和WPF。
我有一个ObservableCollection<RSSFeed>
,在应用程序启动时,从UI线程添加项目到这个集合中。RSSFeed的属性与WPF ListView绑定。稍后,我想异步更新每个RSSFeed。因此,我考虑实现类似于RSSFeed.FetchAsync()
的东西,并在其更新的属性上引发PropertyChanged事件。
我知道ObservableCollection不支持来自除UI线程之外的线程的更新,会抛出NotSupportedException异常。但是由于我不是操作ObservableCollection本身而是更新其项目的属性,所以我可以期望它起作用并看到ListView项更新吗?或者由于PropertyChanged而仍然抛出异常?
编辑:代码
RSSFeed.cs
public class RSSFeed
{
public String Title { get; set; }
public String Summary { get; set; }
public String Uri { get; set; }
public String Encoding { get; set; }
public List<FeedItem> Posts { get; set; }
public bool FetchedSuccessfully { get; protected set; }
public RSSFeed()
{
Posts = new List<FeedItem>();
}
public RSSFeed(String uri)
{
Posts = new List<FeedItem>();
Uri = uri;
Fetch();
}
public void FetchAsync()
{
// call Fetch asynchronously
}
public void Fetch()
{
if (Uri != "")
{
try
{
MyWebClient client = new MyWebClient();
String str = client.DownloadString(Uri);
str = Regex.Replace(str, "<!--.*?-->", String.Empty, RegexOptions.Singleline);
FeedXmlReader reader = new FeedXmlReader();
RSSFeed feed = reader.Load(str, new Uri(Uri));
if (feed.Title != null)
Title = feed.Title;
if (feed.Encoding != null)
Encoding = feed.Encoding;
if (feed.Summary != null)
Summary = feed.Summary;
if (feed.Posts != null)
Posts = feed.Posts;
FetchedSuccessfully = true;
}
catch
{
FetchedSuccessfully = false;
}
}
}
UserProfile.cs
public class UserProfile : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public event CollectionChangeEventHandler CollectionChanged;
private ObservableCollection<RSSFeed> feeds;
public ObservableCollection<RSSFeed> Feeds
{
get { return feeds; }
set { feeds = value; OnPropertyChanged("Feeds"); }
}
public UserProfile()
{
feeds = new ObservableCollection<RSSFeed>();
}
protected void OnPropertyChanged(string name)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
protected void OnCollectionChanged(RSSFeed feed)
{
CollectionChangeEventHandler handler = CollectionChanged;
if (handler != null)
{
handler(this, new CollectionChangeEventArgs(CollectionChangeAction.Add, feed));
}
}
}
MainWindow.xaml.cs
public partial class MainWindow : Window, INotifyPropertyChanged
{
// My ListView is bound to this
// ItemsSource="{Binding Posts}
public List<FeedItem> Posts
{
get
{
if (listBoxChannels.SelectedItem != null)
return ((RSSFeed)listBoxChannels.SelectedItem).Posts;
else
return null;
}
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
// here I load cached feeds
// called from UI thread
// now I want to update the feeds
// since network operations are involved,
// I need to do this asynchronously to prevent blocking the UI thread
}
}
谢谢。
RSSFeed
实例移交给UI线程以添加到集合中。我建议尝试使用BackgroundWorker
类来实现,就像@hbarck在下面建议的那样。 - Chris Shain