Xamarin TabbedPage绑定自定义类启动触发TargetInvocationException求助

数据老陈

2026-5-28

TargetInvocationException when Binding ViewModels to TabbedPage in Xamarin.Forms

Hey folks, I'm hitting a TargetInvocationException right when my Xamarin.Forms app starts up, and it happens when I try to bind custom ViewModels to the two child ContentPages in my TabbedPage. Let me share my code and see if anyone can spot what's going wrong.

My TabbedPage XAML

<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms" 
            xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
            x:Class="DownToledoAPP.Views.InfoPage">
    <ContentPage Icon="tablon.png" BackgroundColor="#3A6DC8" x:Name="tablonpage">
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="*"/>
                <RowDefinition Height="Auto"/>
            </Grid.RowDefinitions>
            <ListView x:Name="tablon" Grid.Row="0" 
                      SelectedItem="{Binding Noticiaelegida}" 
                      ItemsSource="{Binding Noticias}" >
                <ListView.ItemTemplate>
                    <DataTemplate>
                        <Grid>
                            <Grid.RowDefinitions>
                                <RowDefinition Height="Auto"/>
                                <RowDefinition Height="Auto"/>
                                <RowDefinition Height="Auto"/>
                            </Grid.RowDefinitions>
                            <Label Grid.Row="0" Text="{Binding titulo}" FontSize="Large"/>
                            <Label Grid.Row="1" Text="{Binding descripcion}" FontSize="Medium"/>
                            <Grid Grid.Row="2">
                                <Grid.RowDefinitions>
                                    <RowDefinition Height="Auto"/>
                                    <RowDefinition Height="Auto"/>
                                </Grid.RowDefinitions>
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="Auto"/>
                                    <ColumnDefinition Width="Auto"/>
                                </Grid.ColumnDefinitions>
                                <Switch Grid.Column="0" Grid.Row="0" IsToggled="{Binding enprogreso}"/>
                                <Label Grid.Row="0" Grid.Column="1" Text="En progreso"/>
                                <Label Grid.Column="0" Grid.Row="1" Text="{Binding responsable}"/>
                            </Grid>
                        </Grid>
                    </DataTemplate>
                </ListView.ItemTemplate>
            </ListView>
            <Button x:Name="newnoticia" BackgroundColor="#FFCA02" Grid.Row="1" 
                    FontFamily="Cooper Black" TextColor="White" 
                    HorizontalOptions="Center" Text="Abrir nueva actividad"/>
        </Grid>
    </ContentPage>
    <ContentPage Icon="actividades.png" BackgroundColor="#3A6DC8" x:Name="actividadespage">
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="*"/>
                <RowDefinition Height="Auto"/>
            </Grid.RowDefinitions>
            <ListView x:Name="actividades" Grid.Row="0" 
                      ItemsSource="{Binding Actividades}" 
                      SelectedItem="{Binding Actividadelegida}">
                <ListView.ItemTemplate>
                    <DataTemplate>
                        <Grid>
                            <Grid.RowDefinitions>
                                <RowDefinition Height="Auto"/>
                                <RowDefinition Height="Auto"/>
                                <RowDefinition Height="Auto"/>
                            </Grid.RowDefinitions>
                            <Label Grid.Row="0" FontSize="Large" Text="{Binding nombre}"/>
                            <Label Grid.Row="1" Text="{Binding descripcion}"/>
                            <Label Grid.Row="2" FontSize="Small" Text="{Binding horario}"/>
                            <Grid Grid.Row="3">
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="Auto"/>
                                    <ColumnDefinition Width="Auto"/>
                                </Grid.ColumnDefinitions>
                                <Label Grid.Column="0" Text="{Binding responsable}"/>
                                <Label Grid.Column="1" Text="{Binding localizacion}"/>
                            </Grid>
                        </Grid>
                    </DataTemplate>
                </ListView.ItemTemplate>
            </ListView>
            <Button x:Name="newactividad" BackgroundColor="#FFCA02" Grid.Row="1" 
                    FontFamily="Cooper Black" TextColor="White" 
                    HorizontalOptions="Center" Text="Abrir nueva noticia"/>
        </Grid>
    </ContentPage>
</TabbedPage>

Code-behind for InfoPage

public partial class InfoPage : TabbedPage 
{ 
    private CWS cws; 
    private DatosUsuario actualusuario; 

    public InfoPage (string text) 
    { 
        InitializeComponent (); 
        cws = new CWS(); 
        actualusuario = new DatosUsuario(); 
        actualusuario=cws.DescargarInfousuario(text); 
        var alltablon= cargartablon(); 
        var actividades = cargaractividades(); 
        image.Source = actualusuario.foto; 
        name.Text = actualusuario.nombre + " " + actualusuario.apellido1 + " " + actualusuario.apellido2 + " Alias:" + actualusuario.nombreuser; 
        logout.Clicked += salir; 
        userinfo.Clicked += change; 
        newnoticia.Clicked += crearnoticia; 
        newactividad.Clicked += crearactividad; 
        tablonpage.BindingContext = new ViewModel.InfoNoticiasModel(alltablon, actualusuario.idusuario, this); 
        actividadespage.BindingContext = new ViewModel.InfoViewModel(actividades, actualusuario.idusuario, this); 
    } 

    private async void crearactividad(object sender, EventArgs e) 
    { 
        await Navigation.PushAsync(new DetailPage(null, null, "Actividad", actualusuario.idusuario)); 
    } 

    private async void crearnoticia(object sender, EventArgs e) 
    { 
        await Navigation.PushAsync(new DetailPage(null, null, "Noticia", actualusuario.idusuario)); 
    } 

    private List<ActividadesMVVM> cargaractividades() 
    { 
        var noticias = cws.DescargarActividades(actualusuario.idusuario.ToString(),actualusuario.idrol.ToString()); 
        var listamvvm = new List<ActividadesMVVM>(); 
        for (int i = 0; i < noticias.Count; i++) 
        { 
            var actividad = new ActividadesMVVM(); 
            var creador = cws.DescargarNombre(noticias[i].idresponsable.ToString()); 
            actividad.descripcion = noticias[i].descripcion; 
            actividad.horario = noticias[i].horario; 
            actividad...
    }
}

Let's Troubleshoot This

First off, TargetInvocationException is almost always a wrapper for an inner exception that's the real culprit. So your first step should be to dig into that inner exception to get the actual error message.

Step 1: Capture the Inner Exception

Wrap your constructor code in a try-catch block to log or inspect the inner exception:

public InfoPage(string text)
{
    try
    {
        InitializeComponent();
        // Rest of your constructor code here
    }
    catch (TargetInvocationException ex)
    {
        var realException = ex.InnerException;
        Console.WriteLine($"Root cause: {realException.Message}\nStack trace: {realException.StackTrace}");
        throw; // Re-throw to keep debugging flow
    }
}

Step 2: Stop Doing Network Calls in the Constructor

Your code is making synchronous network requests (cws.DescargarInfousuario, cws.DescargarActividades) directly in the constructor. This blocks the UI thread and is a common source of exceptions in Xamarin. Move this logic to an async method like OnAppearing:

public InfoPage(string text)
{
    InitializeComponent();
    // Only set up event handlers here
    logout.Clicked += salir;
    userinfo.Clicked += change;
    newnoticia.Clicked += crearnoticia;
    newactividad.Clicked += crearactividad;
}

protected override async void OnAppearing()
{
    base.OnAppearing();
    try
    {
        cws = new CWS();
        // Wrap sync calls in Task.Run to avoid blocking UI, or better yet, use async versions of your CWS methods
        actualusuario = await Task.Run(() => cws.DescargarInfousuario(text));
        var alltablon = await Task.Run(() => cargartablon());
        var actividades = await Task.Run(() => cargaractividades());

        // Update UI and set BindingContexts once data is loaded
        image.Source = actualusuario.foto;
        name.Text = $"{actualusuario.nombre} {actualusuario.apellido1} {actualusuario.apellido2} Alias:{actualusuario.nombreuser}";
        
        tablonpage.BindingContext = new ViewModel.InfoNoticiasModel(alltablon, actualusuario.idusuario, this);
        actividadespage.BindingContext = new ViewModel.InfoViewModel(actividades, actualusuario.idusuario, this);
    }
    catch (Exception ex)
    {
        Console.WriteLine($"Failed to load data: {ex.Message}");
        // Show a user-friendly error message here
    }
}

Step 3: Validate Your ViewModels

Make sure your InfoNoticiasModel and InfoViewModel are properly implemented:

They should implement INotifyPropertyChanged so bindings work correctly.
All properties referenced in your XAML (like Noticias, Actividades, Noticiaelegida) must exist and match the exact casing.
Add null checks in your ViewModel constructors—if alltablon or actividades is null, handle it gracefully instead of letting it throw.

Step 4: Fix Incomplete Data Loading

Your cargaractividades method cuts off mid-implementation. Make sure you're fully initializing each ActividadesMVVM object and adding it to the list. Also, add null checks for the data returned by cws.DescargarActividades:

private List<ActividadesMVVM> cargaractividades()
{
    var noticias = cws.DescargarActividades(actualusuario.idusuario.ToString(), actualusuario.idrol.ToString());
    var listamvvm = new List<ActividadesMVVM>();
    
    // Guard against null data
    if (noticias == null) return listamvvm;
    
    for (int i = 0; i < noticias.Count; i++)
    {
        var actividad = new ActividadesMVVM();
        var creador = cws.DescargarNombre(noticias[i].idresponsable.ToString());
        
        actividad.descripcion = noticias[i].descripcion;
        actividad.horario = noticias[i].horario;
        actividad.nombre = noticias[i].nombre; // Make sure you set all required properties
        actividad.responsable = creador;
        actividad.localizacion = noticias[i].localizacion;
        
        listamvvm.Add(actividad);
    }
    return listamvvm;
}

Step 5: Ensure UI Thread Safety

When setting BindingContexts, make sure you're doing it on the UI thread. Wrap those lines in Device.BeginInvokeOnMainThread if you're running code in a background task:

Device.BeginInvokeOnMainThread(() =>
{
    tablonpage.BindingContext = new ViewModel.InfoNoticiasModel(alltablon, actualusuario.idusuario, this);
    actividadespage.BindingContext = new ViewModel.InfoViewModel(actividades, actualusuario.idusuario, this);
});

内容的提问来源于stack exchange，提问作者Krever