I tried to use some DataBindings on the listview but nothing is listed.

Model.cs

public class Post
{
    // Columns inside of the Database table

    [PrimaryKey, AutoIncrement]
    public int Id { get; set; }

    [MaxLength(250)]
    public string Experience { get; set; }
}

MainViewModel.cs

private ObservableCollection<Post> _postList;
public  ObservableCollection<Post> PostList
{
    get { return _postList; }
    set { SetProperty(ref _postList, value); }
}

public void ReadDataBase()
{
    using (SQLiteConnection conn = new SQLiteConnection(App.DatabaseLocation))
    {
        conn.CreateTable<Post>();
        var postList = conn.Table<Post>().ToList();
        PostList = new ObservableCollection<Post>(postList);
    }
}

HistoryPage.xaml

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:viewModel ="clr-namespace:TravelRecordApp.ViewModel"
             x:Class="TravelRecordApp.View.HistoryPage">

    <ContentPage.BindingContext>
        <viewModel:MainViewModel/>
    </ContentPage.BindingContext>
    <ListView x:Name="postListView" ItemsSource="{Binding PostList}">
        <ListView.ItemTemplate>
            <DataTemplate>
                <TextCell Text="{Binding Experience}"/>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>
</ContentPage>

HistoryPage.xaml.cs

protected override void OnAppearing()
{
    base.OnAppearing();
    MainViewModel mv = new MainViewModel();
    mv.ReadDataBase();
}

Notes:

After debugging I confirmed that whenever I go to the HistoryPage, the PostList is updated with the new data. So SQL Data reading and page navigation is working fine. I just can not see the contents from the ListView.

I tried also using just List<Post> before ObservableCollection, the result is the same.

CodePudding user response：

the problem in your code is that your xaml is binding to an instance that is different then the one your calling ReadDataBase() function from. try please my solution please:

private ObservableCollection<Post> _postList;
public  ObservableCollection<Post> PostList
{
    get { return _postList; }
    set { _postList =value; }
}

remove the <ContentPage.BindingContext> from xaml;

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:viewModel ="clr-namespace:TravelRecordApp.ViewModel"
             x:Class="TravelRecordApp.View.HistoryPage">
  <ContentPage.Content>
    <ListView x:Name="postListView" ItemsSource="{Binding PostList}">
        <ListView.ItemTemplate>
            <DataTemplate>
                <TextCell Text="{Binding Experience}"/>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>
  </ContentPage.Content>
</ContentPage>

in the code behind

private MainViewModel viewModel;
public HistoryPage() // constructor 
        {
            InitializeComponent();
            viewModel = new MainViewModel();
            this.BindingContext = viewModel;
        }
protected override void OnAppearing()
{
    base.OnAppearing();
    viewModel.ReadDataBase();
}

CodePudding user response：

The root cause is that you only need add post to PostList after var postList = conn.Table().ToList();This works well on my side.

Below is the ViewModel code:

    public class HistoryPageViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private ObservableCollection<Post> _postList;
    public ObservableCollection<Post> PostList
    {
        get => _postList;

        set { 
            _postList = value;
        }
    }
    public HistoryPageViewModel()
    {
        PostList = new ObservableCollection<Post>();
    }

    public void ReadDataBase()
    {
        using (SQLiteConnection conn = new SQLiteConnection(App.DatabaseLocation))
        {
            conn.CreateTable<Post>();
            var postList = conn.Table<Post>().ToList();

            foreach (var post in postList)
            {
                PostList.Add(post); 
            }
        }
    }
}

Below is the code behind:

 public partial class HistoryPage : ContentPage
{
    HistoryPageViewModel vm;
    public HistoryPage()
    {
        InitializeComponent();

        vm = new HistoryPageViewModel();
        this.BindingContext = vm;
    }

    protected override void OnAppearing()
    {
        base.OnAppearing();

        vm.ReadDataBase();
    }
    private void Button_Clicked(object sender, EventArgs e)
    {
        Navigation.PushAsync(new NewTravelPage());
    }
}

Below is the code in xaml:

    <StackLayout HorizontalOptions="Center" VerticalOptions="FillAndExpand" Padding="10">
    <ListView  ItemsSource="{Binding PostList}" >
        <ListView.ItemTemplate>
            <DataTemplate>
                <ViewCell>
                    <Label Text="{Binding Experience}" TextColor="Black" FontSize="Large"></Label>
                </ViewCell>                       
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>

    <Button Clicked="Button_Clicked"></Button>
</StackLayout>