Question

我在listview上使用了ObservableCollection。 ObservableCollection使用异步方法从Web服务正确获取其数据，然后解析它并使用NewsProxyParser上的Add方法填充ObservableCollection（String thing，out ObservableCollection newsList）方法，但是我无法使用binded ObservableCollection。

我是UWP的新手，所以我认为异步方法在与GUI不同的线程上运行。如何正确执行绑定以使用从Web服务获取的数据更新GUI？

我的XAML：

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <ListView Name="ListViewNews" ItemsSource="{x:Bind NewsCollection, Mode=OneWay}" IsItemClickEnabled="True" ItemClick="ListView_ItemClick">
        <ListView.ItemTemplate>

            <DataTemplate x:DataType="data:News">

                <RelativePanel Margin="0,16" >
                    <Image Name="x:Thumb" Source="{x:Bind thumbnailUrl}" Width="96" Height="96" RelativePanel.AlignLeftWithPanel="True" Margin="0,0,16,0"></Image>
                    <TextBlock Name="x:Title" Text="{x:Bind title}" FontSize="22" FontWeight="Bold"  RelativePanel.RightOf="x:Thumb"></TextBlock>
                    <TextBlock Name="x:Date" Text="{x:Bind dateString}" FontSize="12" FontWeight="Light" Foreground="Gray" RelativePanel.RightOf="x:Thumb" RelativePanel.Below="x:Title"></TextBlock>
                    <TextBlock Name="x:Text" Text="{x:Bind newsText}" Foreground="Gray"  RelativePanel.RightOf="x:Thumb" RelativePanel.Below="x:Date"></TextBlock>
                </RelativePanel>

            </DataTemplate>

        </ListView.ItemTemplate>                       
    </ListView>
</Grid>

和cs：

public sealed partial class NewsPage : Page
{

    private ObservableCollection<News> NewsCollection;

    public NewsPage()
    {
        NewsRequest();
        this.InitializeComponent();                     
    }

    private async void NewsRequest()
    {
        //Fetch News from web
        string response =  await NewsProxy.GetNews("TokenX");
        //Parse News to add to NewsCollection
        bool success = NewsProxy.NewsProxyParser(response, out NewsCollection);

        // success is true and NewsCollection has new updated values

        if (success)
        {
            News n = new News();
            n.title = "Just to trigger collectionchanged";
            n.newsText = "dadada";
            n.order = 1;
            NewsCollection.Add(n);
            Debug.WriteLine("Still No GUI updated!!!");

        }

    }

}

Answer 1

ObservableCollection<>仅通知收集更改，例如添加和删除项目。只要替换整个集合，就需要使NewsCollection成为依赖属性，以通知XAML UI有关更改的信息。

public ObservableCollection<News> NewsCollection
{
    get { return (ObservableCollection<News>)GetValue(NewsCollectionProperty); }
    set { SetValue(NewsCollectionProperty, value); }
}

public static readonly DependencyProperty NewsCollectionProperty =
    DependencyProperty.Register("NewsCollection", typeof(ObservableCollection<News>), typeof(NewsPage), new PropertyMetadata(null));

private async void NewsRequest()
{
    //Fetch News from web
    string response =  await NewsProxy.GetNews("TokenX");
    //Parse News to add to NewsCollection
    ObservableCollection<News> newsCollection;
    bool success = NewsProxy.NewsProxyParser(response, out newsCollection);
    NewsCollection = newsCollection;

    // success is true and NewsCollection has new updated values

    if (success)
    {
        News n = new News();
        n.title = "Just to trigger collectionchanged";
        n.newsText = "dadada";
        n.order = 1;
        NewsCollection.Add(n);
        Debug.WriteLine("Still No GUI updated!!!");
    }
}

UWP ObservableCollection，来自webservice的数据未更新GUI

1 个答案: