Question

我正在尝试将Observable对象集合绑定到列表视图。我在视图模型中放了一个调试，它显示集合在那里。但它似乎并没有显示在前端。

这是Xaml：

<StackLayout>      



    <ListView
              x:Name="dataList"                    
              ItemsSource="{Binding routeLabels}" >

        <ListView.ItemTemplate>
            <DataTemplate>
                <TextCell Text="{Binding RouteName}"/>
            </DataTemplate>

        </ListView.ItemTemplate>

    </ListView>

</StackLayout>

背后的代码：

public partial class DriverDashboardView : ContentPage
{
    private DriverDashboardViewModel driverdashboardviewmodel;


    public DriverDashboardView()
    {

        InitializeComponent();

        this.Title = "Driver's Dashboard";
        BindingContext = driverdashboardviewmodel = new DriverDashboardViewModel();

    }

    protected async override void OnAppearing()
    {
        base.OnAppearing();
        await driverdashboardviewmodel.GetLabelInfo();
    }   

}

和视图模型：

public class DriverDashboardViewModel:BaseViewModel,INotifyPropertyChanged
{


    public DriverDashboardViewModel()
    {


    }

    public async Task GetLabelInfo()
    {
        _routelabels = await service.return_label_info();

    }

    // property change handler to bind to UI
    private ObservableCollection<RouteInfo> _routelabels;
    public ObservableCollection<RouteInfo> routeLabels
    {
        get { return _routelabels; }
        set
        {
            if (Equals(value, _routelabels)) return;
            _routelabels = value;
            OnPropertyChanged(nameof(routeLabels));
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this,
                new PropertyChangedEventArgs(propertyName));
    }
}

和RouteInfo类：

public class RouteInfo
{
    public string RouteName { get; set; }
    public int Stops { get; set; }
    public string DayOf { get; set; }

}

正如我所说，我在视图模型中进行了调试，我可以看到数据存在。但我不能在前端看到它。

有什么想法吗？

Answer 1

在DriverDashboardViewModel.GetLabelInfo()方法中，您要将结果分配给_routelabels。但是_routelabels并没有调用OnPropertyChanged()，这是更改要求用户重新评估其绑定所必需的。{/ p>

我建议将await service.return_label_info();的结果直接分配给routeLabels。

但您也可以按照现在的方式保留GetLabelInfo()代码，只需在_routelabels分配后添加以下内容即可手动触发UI更新：OnPropertyChanged(nameof(routeLabels));

总而言之，请做以下两件事之一：

public async Task GetLabelInfo() {
    routeLabels = await service.return_label_info();
}

或者：

public async Task GetLabelInfo() {
    _routelabels = await service.return_label_info();
    OnPropertyChanged(nameof(routeLabels));
}

绑定到ListView Xamarin Froms

1 个答案: