Question

Application
x:Class="sqlasynctest.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:sqlasynctest"
xmlns:viewModel="using:sqlasynctest.ViewModel"
RequestedTheme="Light">
<Application.Resources>
    <ResourceDictionary>
        <viewModel:ViewModelLocator x:Key="Locator" />
    </ResourceDictionary>
</Application.Resources>

public class ViewModelLocator
{
    public ViewModelLocator()
    {
        ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);

        if (!SimpleIoc.Default.IsRegistered<IDal>())
        {
            SimpleIoc.Default.Register<IDal, Dal>();
        }


        SimpleIoc.Default.Register<MainViewModel>();
    }
    public MainViewModel Main
    {
        get
        {
            return ServiceLocator.Current.GetInstance<MainViewModel>();
        }
    }
    public static void Cleanup()
    {
        // TODO Clear the ViewModels
    }

}

MainViewModel

public class MainViewModel : ViewModelBase
{
    private readonly IDal _iDal;

    private IList<User> _user;

    public IList<User> Users
    {
        get { return _user; }
        set { Set("Users", ref _user, value); }
    }
    public MainViewModel(IDal dal)
    {
        _iDal = dal;
        LoadDataCommand = new RelayCommand(async () => await LoadData());
    }
    public ICommand LoadDataCommand { get; private set; }
    public async Task LoadData()
    {
        Users = await _iDal.LoadAllUser();
    }
}

的MainPage

<Page
x:Class="sqlasynctest.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:sqlasynctest"
DataContext="{Binding Main, Source={StaticResource Locator}}"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"> 
<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*"/>
        <ColumnDefinition Width="20"/>
        <ColumnDefinition Width="*"/>
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition Height="140"/>
        <RowDefinition Height="*"/>
    </Grid.RowDefinitions>

    <ListBox Grid.Column="0" Grid.Row="1" SelectionMode="Single"
             ItemsSource="{Binding Users}" Margin="120,0,0,40">
        <ListBox.ItemTemplate>
            <DataTemplate>
                <StackPanel Orientation="Horizontal">
                    <TextBlock Text="{Binding FirstName}"/>
                    <TextBlock Text="{Binding LastName}"/>
                </StackPanel>
            </DataTemplate>
        </ListBox.ItemTemplate>
        </ListBox>
</Grid>

表和方法很好，但我认为绑定是错误的，帮助我 LoadData（）方法不会在任何地方调用。

我得到了一个解决方案

protected override void OnNavigatedTo(NavigationEventArgs e)
    {
        var viewModel = (MainViewModel)DataContext;
        if (viewModel != null)
        {
            viewModel.LoadData();
        }

我不想触摸MainPage.cs 在xaml代码中执行此操作的任何其他方法

Answer 1

您的问题是您的收藏品是List。它不会通知UI有关chnages的信息。用户ObservableCollection代替它，它将开始工作。

Answer 2

您的视图模型中有LoadDataCommand，但不会从任何地方调用它。这里没有魔法 - 你必须从XAML或代码隐藏文件调用它。以下是在XAML中完成此操作的方法：

安装Microsoft.Xaml.Behaviors.Uwp.Managed NuGet包。

修改主页的XAML：

<Page
...
xmlns:i="using:Microsoft.Xaml.Interactivity"
xmlns:c="using:Microsoft.Xaml.Interactions.Core"> 

<i:Interaction.Behaviors>
    <c:EventTriggerBehavior EventName="Loaded">
        <c:InvokeCommandAction Command="{Binding LoadDataCommand}"/>
    </c:EventTriggerBehavior>
</i:Interaction.Behaviors>

<Grid ...>

从代码隐藏文件中删除重写的OnNavigatedTo方法。

LoadDataCommand

MainPage。

Sqlite数据不显示

2 个答案: