Question

我已经在这个问题上坐了好几个小时了，我有这个部分xaml代码：

<TextBlock Text="{Binding temprature}" Height="30" HorizontalAlignment="Left" Margin="13,119,0,0" Name="textBlock1" VerticalAlignment="Top" Width="68" />
            <TextBlock Height="30" HorizontalAlignment="Left" Name="commentsTextBlock" Text="Comments:" VerticalAlignment="Bottom" Margin="12,0,0,-31" />
            <ListBox Margin="2,785,-14,-33" ItemsSource="{Binding comments}" DataContext="{Binding}" Name="commentsListBox">
                <ListBox.ItemTemplate>
                    <DataTemplate>
                        <StackPanel Orientation="Horizontal" Margin="0,0,0,17">
                            <StackPanel Width="311">
                                <TextBlock Text="{Binding poster_username}" TextWrapping="NoWrap" Style="{StaticResource PhoneTextSubtleStyle}" TextTrimming="WordEllipsis" Width="Auto" Foreground="White" FontFamily="Segoe WP Semibold" />
                                <TextBlock Text="{Binding comment_text}" TextWrapping="Wrap" Margin="12,-6,12,0" Style="{StaticResource PhoneTextSubtleStyle}" TextTrimming="WordEllipsis" MaxHeight="100" />
                            </StackPanel>
                        </StackPanel>
                    </DataTemplate>
                </ListBox.ItemTemplate>
            </ListBox>

我有这个类（Thread），其中包含应该在ListBox中显示的注释列表。

    public class Thread : INotifyPropertyChanged
{
    public string title { get; set; }
    public string deal_link { get; set; }
    public string mobile_deal_link { get; set; }
    public string deal_image { get; set; }
    public string deal_image_highres { get; set; }
    public string description { get; set; }
    public string submit_time { get; set; }
    public bool hot_date { get; set; }
    public string poster_name { get; set; }
    public double temperature { get; set; }
    public double price { get; set; }
    public int timestamp { get; set; }
    public string expired { get; set; }
    public Forum forum { get; set; }
    public Category category { get; set; }
    public object merchant { get; set; }
    public object tags { get; set; }
    public int thread_id { get; set; }
    public string visit_link { get; set; }
    public string hot_time { get; set; }
    public int comment_count { get; set; }
    public string availability { get; set; }
    public string can_vote { get; set; }
    public string seen { get; set; }

    public List<Comment> comments { get; set; }
    public event PropertyChangedEventHandler PropertyChanged;

    public void Convert2Unicode()
    {
        UnicodeEncoding unicode = new UnicodeEncoding();
        Byte[] encodedBytes = unicode.GetBytes(title);
        title = String.Format("[{0}]", title);


    }


    private void NotifyPropertyChanged(String propertyName)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (null != handler)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public void SetComments(string content)
    {
        PaginatedComments commentsList;
        this.comments.Clear();

        DataContractJsonSerializer serializer =
        new DataContractJsonSerializer(typeof(PaginatedComments));
        using (MemoryStream ms = new MemoryStream(Encoding.Unicode.GetBytes(content)))
        {
            commentsList = (PaginatedComments)serializer.ReadObject(ms);
        }


        foreach (var thread in commentsList.data.comments)
        {
            this.comments.Add(thread);
        }

    }
    public Thread()
    {
        comments = new List<Comment>();

    }
    public void addComments()
    {
        List<string> parameters = new List<string>();
        parameters.Add("thread_id=" + thread_id);
        parameters.Add("results_per_page=10");
        parameters.Add("page=1");
        // Set the data context of the listbox control to the sample data
        APICalls.makeRequest(APICalls.ViewingPaginatedComments, parameters, SetComments);

    }
    //
    // Sets the "Seen" variable depending if the item is new (since the last time the application was opened
    //
    public void updateNewItems()
    {
        try
        {
            int last_seen = (int)IsolatedStorageSettings.ApplicationSettings["lastrun"];

            if (last_seen < timestamp)
            {
                seen = "New";
            }
            else
            {
                seen = "";
            }
        }
        catch (System.Exception e)
        {
            IsolatedStorageSettings.ApplicationSettings["lastrun"] = APICalls.GetIntTimestamp();
            IsolatedStorageSettings.ApplicationSettings.Save();
            MessageBox.Show(e.Message);
        }

        IsolatedStorageSettings.ApplicationSettings["lastrun"] = APICalls.GetIntTimestamp();
        IsolatedStorageSettings.ApplicationSettings.Save();

    }
}
public class Comment
{
    public string poster_username { get; set; }
    public string post_date { get; set; }
    public string comment_text { get; set; }
    public int timestamp { get; set; }
    public int like_count { get; set; }
    public string comment_edit_text { get; set; }
}

public class CommentData
{
    public List<Comment> comments { get; set; }
    public int comment_count { get; set; }
    public int total_comments { get; set; }
}

public class PaginatedComments
{
    public string response_status { get; set; }
    public CommentData data { get; set; }
}

如果我在将DataCotext更改为此特定线程之前将注释加载到线程中。注释会显示，但是当我在更改DataContext并导航到页面后更新注释时，注释不会显示（我在xaml页面的其余部分中有其他字段绑定到同一个实例并且它们工作正常。评论不起作用！

非常感谢你的帮助！感谢

Answer 1

您应该使用

public ObservableCollection<Comment> comments{ get; set;}

而不是

public List<Comment> comments { get; set; }

ObservableCollection会在添加或删除其中一个项目（在本例中为Comment）时向视图发送更新通知。

注意：它不会更新评论。要将项目绑定到Comment更新，Comment必须实现INotifyPropertyChanged。

Answer 2

您的属性很简单List<T>。当事情发生变化时，需要使用事件来发信号通知Silverlight。

当添加/删除项目时，List<T>不会引发任何事件，因此Silverlight无法检测到新项目，因此不会更新UI。使这项工作最简单的方法通常是使用ObservableCollection<T>而不是列表。此集合将引发Silverlight知道要听的事件。

请注意，为了使其工作，您不应该从U / I（Dispatcher）线程之外的任何其他线程调用Add / Remove / Clear，因为Silverlight控件不是线程安全的（并且在线程上引发了事件执行添加/删除/清除调用）。要做到这一点，只需确保从SetComments方法中调用Dispatcher.BeginInvoke（因为它似乎是从你的提取机制发生的回调）。

或者，您也可以在获取注释时重新生成一个全新的List对象，并在SetComments方法中引发NotifyPropertyCHanged事件，但这会导致丢失当前选择并将列表重置为顶部，这可能不是什么你想做什么。

WP7 ListBox绑定不会更新

2 个答案: