Question

这是我的Xamarin Forms应用程序中的代码，该应用程序应使用Activities DetaledActivity列表填充xaml ListView，该列表从上一页填充。当我单步执行并调试代码时，_activities包含许多项目，但它们不会显示在xaml页面中。

如果我使用此页面的构造函数中的项目填充列表，那么我可以单击这些单元格，但不会显示任何文本。

public class DetailedActivityPageViewModel : _ViewModelBase
{
    INavigationService _navigationService;
    public DetailedActivityPageViewModel(INavigationService navigationService)
    {
        _navigationService = navigationService;
    }

    public override void OnNavigatedTo(NavigationParameters parameters)
    {
        base.OnNavigatedTo(parameters);
        if (parameters.ContainsKey("properties"))
        {
            var localAcs = new List<DetailedActivity>();
            var properties = (Dictionary<string, object>)parameters["properties"];
            foreach (var prop in properties)
            {
                if (prop.Value != null)
                    localAcs.Add(new DetailedActivity { Key = prop.Key.ToString(), Value = prop.Value.ToString() });
            }
            _activities = localAcs;
        }
    }

    private IEnumerable<DetailedActivity> _activities;
    public IEnumerable<DetailedActivity> Activities { get { return _activities; } set { SetProperty(ref _activities, value, "Activities"); } }
}


public class DetailedActivity
{
    public string Key;
    public string Value;
}

<ListView ItemsSource="{Binding Activities}">
    <ListView.ItemTemplate>
        <DataTemplate>
            <ViewCell>
                <StackLayout Orientation="Horizontal">
                    <Label Text="{Binding Key}" />
                    <Label Text="{Binding Value}" />
                </StackLayout>
            </ViewCell>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

Answer 1

我会尝试使用ObservableCollection代替localAcs代替List。使用ObservableCollection时，应在ObservableCollection添加或删除元素时更新绑定。在添加元素之前，您可能需要将_activities设置为`localAcs'，例如：

public override void OnNavigatedTo(NavigationParameters parameters)
{
    base.OnNavigatedTo(parameters);
    if (parameters.ContainsKey("properties"))
    {
        var localAcs = new List<DetailedActivity>();
        _activities = localAcs;
        var properties = (Dictionary<string, object>)parameters["properties"];
        foreach (var prop in properties)
        {
            if (prop.Value != null)
                localAcs.Add(new DetailedActivity { Key = prop.Key.ToString(), Value = prop.Value.ToString() });
        }
    }
}

未从NavigationParameters更新ListView源

1 个答案: