Populating listview from a list

Issue

With the inspiration of an example, "Listing Colors with BoxView" given in Xamarin documenation https://docs.microsoft.com/en-us/xamarin/xamarin-forms/user-interface/boxview , I've been trying to populate my listview in the same way. However nothing would show up.

In my class PostList which creates an object looks something like this:

public String Body { get; set; }
public String Subject { get; set; }
public Coordinate Position { get; set; }

private List<Post> all = new List<Post>();

public PostList(List<Post> list)
{
       
        all = list;
        method();
}

public void method()
{
        List<PostList> All = new List<PostList>();
       
       foreach(Post x in all)
       {
          PostList Pl = new PostList
          {
                
                Subject = x.getSubject(),
                Body = x.getBody(),
                Position = x.getCoordinate()
          };
          All.Add(Pl);
      }
}
public static IList<PostList> All { set; get; }

And the XAML class for displaying is given below:

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         xmlns:local="clr-namespace:EE.Model"
         x:Class="EE.View.CWT"
         NavigationPage.HasNavigationBar="False"
         NavigationPage.BackButtonTitle="False"
         ControlTemplate="{StaticResource Template}">

    <ListView SeparatorVisibility="Default"
          ItemsSource="{x:Static local:PostList.All}">
    

    <ListView.RowHeight>
        <OnPlatform x:TypeArguments="x:Int32">
            <On Platform="iOS, Android" Value="180" />
        </OnPlatform>
    </ListView.RowHeight>
    <ListView.WidthRequest Value="20"/>

    <ListView.ItemTemplate>
        <DataTemplate>
            <ViewCell>
                <ContentView Margin="5,5,5,5">
                    <Frame OutlineColor="LightGray">
                        <StackLayout>
                            <StackLayout Orientation="Horizontal">
                                <StackLayout x:Name="SL" Padding="0">
                                    <Label x:Name="Title" Text="{Binding Subject}"/>
                                </StackLayout>
                            </StackLayout>
                         </StackLayout>
                    </Frame>
                </ContentView>
            </ViewCell>
        </DataTemplate>
    </ListView.ItemTemplate>

I have checked that the list "All" is populated, but I can't figure out what should be done for it to display.

Solution

There are two All in your codes above.

One is

public static IList<PostList> All { set; get; },

another is in your method()

List<PostList> All = new List<PostList>();

Try to change it to keep them consistent:

public void method()
{
   All = new List<PostList>();
   
   foreach(Post x in all)
   {
      PostList Pl = new PostList
      {
            
            Subject = x.getSubject(),
            Body = x.getBody(),
            Position = x.getCoordinate()
      };
      All.Add(Pl);
  }
}

I'm also confused about how you instantiate your ViewModel.where do you pass the parameter with this public PostList(List<Post> list) constructor ?

we usually do like this :

<ListView SeparatorVisibility="Default"
      x:Name ="listview">
    ...

</ListView>

in code behind:

public YourPage()
  {
      InitializeComponent();
      PostList list = new PostList(your List<Postlist>);
      listview.ItemsSource = list.All;
  }

viewmodel:

public class PostList
{

  public String Body { get; set; }
  public String Subject { get; set; }
  public Coordinate Position { get; set; }
  private List<Post> all = new List<Post>();
  public PostList(List<Post> list)
  {
   
    all = list;
    method();
  }

  public void method()
  {
    All = new List<PostList>();
   
    foreach(Post x in all)
    {
      PostList Pl = new PostList
      {
            
            Subject = x.getSubject(),
            Body = x.getBody(),
            Position = x.getCoordinate()
      };
      All.Add(Pl);
    }  
  }
  public IList<PostList> All { set; get; }
}

or use the x:Static resource:

public class PostList
{

  public String Body { get; set; }
  public String Subject { get; set; }
  public Coordinate Position { get; set; }
  private static List<Post> all = new List<Post>();
  static PostList()
  {

    all = xxx;//here create a List<Post>
    method();
  }

  public static void method()
  {
    All = new List<PostList>();

    foreach(Post x in all)
    {
      PostList Pl = new PostList
      {

        Subject = x.getSubject(),
        Body = x.getBody(),
        Position = x.getCoordinate()
      };
      All.Add(Pl);
    }  
   }
  public IList<PostList> All { set; get; }
}

then you could binding in your xaml like:

<ListView SeparatorVisibility="Default"
      ItemsSource="{x:Static local:PostList.All}">
  ...
</ListView>

Answered By - Leo Zhu - MSFT