Question

在我的Windows Phone 8应用程序中，我有下面的列表框

<ListBox x:Name="ListBox1"  ItemsSource="{Binding}">
<ListBox.ItemTemplate>
<DataTemplate>
<Grid>
<TextBlock  Text="{Binding snippet.DownloadPercentage}" 
TextWrapping="Wrap"
FontFamily="Portable User Interface"/>
</Grid>
</DataTemplate>
</ListBox.ItemTemplate>

我正在下载文件asyn，并希望将进度百分比提供给UI，如下所示; 但它不会更新UI。它始终显示0是初始int值。如果我在主线程上访问DownloadPercentage属性它没有问题地更新。

 private void ClientOnDownloadProgressChanged(object sender, DownloadProgressChangedEventArgs downloadProgressChangedEventArgs)
        {
            // not working
            item.snippet.DownloadPercentage = progressPercentage;

            // not working      
            Dispatcher.BeginInvoke(delegate {
               item.snippet.DownloadPercentage = progressPercentage;

            });    
            // not working
            ProgressChangedEventHandler workerProgressChanged = delegate {
                item.snippet.DownloadPercentage = progressPercentage;
            };
            BackgroundWorker worker = new BackgroundWorker();
            worker.WorkerReportsProgress = true;
            worker.ProgressChanged += workerProgressChanged;
            worker.ReportProgress(progressPercentage);

            // WORKING!
            #region ProgressIndicator
            _progressIndicator.Text = string.Format("Downloading ({0}%) {1}", progressPercentage, item.snippet.Title);
            _progressIndicator.IsVisible = true;
            _progressIndicator.IsIndeterminate = true;
            SystemTray.SetProgressIndicator(this, _progressIndicator);
            #endregion

        }

我该怎么办？

溶液; 在@DecadeMoon的提示后，我必须在Snippet类上实现INotifyPropertyChanged。

public class Snippet : INotifyPropertyChanged
    { 
 [JsonProperty("downloadPercentage")]
        public int DownloadPercentage
        {
            get { return _downloadPercentage; }
            set
            {
                _downloadPercentage = value;
                RaisePropertyChanged("DownloadPercentage");
            }
        }
 public event PropertyChangedEventHandler PropertyChanged;
        private void RaisePropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }

Answer 1

您在视图中绑定的属性必须实现INotifyPropertyChanged。在您的情况下，您已绑定到snippet.DownloadPercentage，因此代码段类必须实现INotifyPropertyChanged，并且必须在PropertyChanged属性的setter中引发DownloadPercentage事件。

您还必须确保只修改UI线程中的DownloadPercentage属性，否则如果从另一个线程修改，您将获得异常。这通常通过使用调度程序来完成：

Dispatcher.BeginInvoke(() =>
{
    item.snippet.DownloadPercentage = progressPercentage;
});

Windows Phone从后台线程更新绑定

1 个答案: