I try to load Data of the type "User" in a ListView Template. It recognises everything. But for some reason I get this exception when I try to open the site that contains the ListView: System.Reflection.TargetInvocation exception. I get 0 errors just this exception.

C# Code looks like this (I am really new to C#, and this is probably not best practice)

using System.Collections.ObjectModel;

namespace GoogleMessenger.Pages;

public partial class ContactPage : ContentPage
{
    public ObservableCollection<User> Contact { get; set; } = new ObservableCollection<User>();
    public List<User> UserList { get; set; }
    public ContactPage()
    {
        InitializeComponent();
        BindingContext = this;

    }

    protected override void OnAppearing()
    {
        UserList = new List<User>()
        {
            new User() {Username = "something", Email = "[email protected]", LastMessage = "something! Lorem Ipsum...", ImageSource = "dotnet_bot.jpg"},
            new User() {Username = "something", Email = "[email protected]", LastMessage = "Lorem 10min something...", ImageSource = "dotnet_bot.jpg.jpg"},

        };


        if (!UserList.Any())
        {
            foreach (var user in UserList)
            {
                var userCopy = user;
                Contact.Add(userCopy);
            }
        }
        base.OnAppearing();
    }
      
}

And my XAML Code looks like this

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:pages="clr-namespace:GoogleMessenger.Pages"
             x:Class="GoogleMessenger.Pages.ContactPage"
             Title="ContactPage"
             >
    <ContentPage.BindingContext>
        <pages:ContactPage></pages:ContactPage>
    </ContentPage.BindingContext>
 
    <ListView ItemsSource="{Binding Contact}">
    <ListView.ItemTemplate>
        <DataTemplate>
            <ViewCell>
                <Grid Padding="10">
                    <Grid.RowDefinitions>
                        <RowDefinition Height="Auto" />
                        <RowDefinition Height="Auto" />
                    </Grid.RowDefinitions>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="Auto" />
                        <ColumnDefinition Width="Auto" />
                    </Grid.ColumnDefinitions>
                    <Image Grid.RowSpan="2"
                           Source="{Binding ImageSource}"
                           Aspect="AspectFill"
                           HeightRequest="60"
                           WidthRequest="60" />
                    <Label Grid.Column="1"
                           Text="{Binding Username}"
                           FontAttributes="Bold" />
                    <Label Grid.Row="1"
                           Grid.Column="1"
                           Text="{Binding LastMessage}"
                           FontAttributes="Italic"
                           VerticalOptions="End" />
                </Grid>
            </ViewCell>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>
</ContentPage>

CodePudding user response：

get rid of this

<ContentPage.BindingContext>
    <pages:ContactPage></pages:ContactPage>
</ContentPage.BindingContext>

you are already assigning the BindingContext in the codebehind so this is redundant, and not the proper syntax to use when your page is it's own BindingContext

CodePudding user response：

To begin with, as Jason suggested, don't set multiple BindingContext. You either set the BindingContext in Xaml or Code-behind.

In addiction, you can try to set the item source of ListView like below:

Code-behind:

public partial class MainPage : ContentPage
{
    readonly IList<User> source;
    public ObservableCollection<User> Contact { get; private set; } 

    public MainPage()
    {
       InitializeComponent();
       source= new List<User>();
       CreateUserCollection();

       BindingContext = this;   
   }

    private void CreateUserCollection()
    {
        source.Add(new User() { Username = "something", Email = "[email protected]", LastMessage = "something! Lorem Ipsum...", ImageSource = "dotnet_bot.png" });
        source.Add(new User() { Username = "something", Email = "[email protected]", LastMessage = "Lorem 10min something...", ImageSource = "dotnet_bot.png" });

        Contact = new ObservableCollection<User>(source);
    }

}