dependecy injection

Question

dependecy injection

Eduardo Gomez Romero 1,375

For some reason, I am getting a cast error when registering a view Model and I don't know what is going on

 public static MauiApp CreateMauiApp() {
        var builder = MauiApp.CreateBuilder();
        builder
            .UseMauiApp<App>()
            .UseMauiCommunityToolkit()
            .ConfigureFonts(fonts => {
                fonts.AddFont("MaterialIcons-Regular.ttf", "MaterialSymbol");
                fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
                fonts.AddFont("OpenSans-Semibold.ttf", "OpenSansSemibold");
            }).ConfigureMauiHandlers(handlers => {

                handlers.AddHandler<BorderlessEntry, EntryHandler>();
            });

        BorderlessEntryHandler.ApplyCustomHandler();

        builder.Services.AddSingleton<AppShell>();

        builder.Services.AddSingleton<LoginPage, LoginViewModel>();

        builder.Services.AddSingleton<MainPage, MainViewModel>();

        return builder.Build();
    }
}

Login Page view Model

public partial class LoginPageViewModel : ObservableObject {

    [RelayCommand]
    void ChangeVisibility() { }
}

public partial class LoginPage : ContentPage {
    public LoginPage(LoginPageViewModel loginView) {
        InitializeComponent();
        BindingContext = loginView;
    }

}

System.Reflection.TargetInvocationException: 'Exception has been thrown by the target of an invocation.'

Net8

Windows, Android

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Answer 1

Yonglun Liu (Shanghai Wicresoft Co,.Ltd.) 50,166 Microsoft External Staff

Hello,

This issue is caused by incorrect usage of the AddSingleton method.

If you pass in two parameters builder.Services.AddSingleton<MainPage, MainViewModel>(); when using this method, according to the description in the ServiceCollectionServiceExtensions.AddSingleton Method, you need to pass in a Service interface and its implementation class.

AddSingleton<TService,TImplementation>(IServiceCollection): Adds a singleton service of the type specified in TService with an implementation type specified in TImplementation to the specified IServiceCollection.

For example, the official documentation gives the demonstration of mauiAppBuilder.Services.AddTransient<ISettingsService, SettingsService>();. Although this demonstration method is AddTransient, it is still applicable to the AddSingleton method.

Since MainViewModel is not an implementation class of MainPage, a type conversion error occurred when the program was created.

Workaround:

Register these classes individually.

builder.Services.AddSingleton<MainPage>();
builder.Services.AddSingleton<MainViewModel>();
builder.Services.AddSingleton<LoginPage>();
builder.Services.AddSingleton<LoginViewModel>();

Best Regards,

Alec Liu.

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Eduardo Gomez Romero 1,375

I get the same issue

do you think is the problem of my page?

Login page

<ContentPage
    x:Class="TalkMe.Views.LoginPage"
    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:controls="clr-namespace:TalkMe.Controls"
    xmlns:fonts="clr-namespace:TalkMe.Fonts"
    xmlns:vm="clr-namespace:TalkMe.ViewModels"
    x:DataType="vm:LoginPageViewModel">
    <VerticalStackLayout
        Padding="40"
        Spacing="40">
        <Label
            FontFamily="MaterialSymbol"
            FontSize="100"
            HorizontalTextAlignment="Center"
            Text="{x:Static fonts:IconFont.Cloud}"
            TextColor="#1313CB" />
        <controls:CustomEntry
            IconFont="{x:Static fonts:IconFont.Cloud}"
            PlaceholderText="Email" />
        <controls:CustomEntry
            IconFont="{x:Static fonts:IconFont.Password}"
            IsPassword="True"
            PasswordVisibilityCommand="{x:Binding ChangeVisibilityCommand}"
            PaswordVisibleIcon="{x:Static fonts:IconFont.Visibility}"
            PlaceholderText="Password" />
        <Button
            FontAttributes="Bold"
            Text="Login" />
        <Label
            HorizontalTextAlignment="Center"
            Text="Do not have an account? Register here" />
    </VerticalStackLayout>
</ContentPage>

Cutom control

<ContentView
    x:Class="TalkMe.Controls.CustomEntry"
    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    x:Name="EntryWithIcon">
    <Border Background="White">
        <Border.StrokeShape>
            <RoundRectangle CornerRadius="8" />
        </Border.StrokeShape>
        <Grid
            Padding="2"
            BindingContext="{x:Reference EntryWithIcon}"
            ColumnDefinitions="Auto,*,Auto">
            <BoxView
                Margin="40,0,0,0"
                BackgroundColor="Black"
                HorizontalOptions="End"
                WidthRequest="2" />
            <Label
                FontFamily="MaterialSymbol"
                FontSize="Large"
                HorizontalOptions="Center"
                Text="{x:Binding IconFont}"
                TextColor="Black"
                VerticalOptions="Center" />
            <Entry
                Grid.Column="1"
                IsPassword="{x:Binding IsPassword}"
                Placeholder="{x:Binding PlaceholderText}"
                TextColor="Black" />
            <Label
                Grid.Column="2"
                FontFamily="MaterialSymbol"
                FontSize="Large"
                HorizontalOptions="Center"
                Text="{x:Binding PaswordVisibleIcon}"
                TextColor="Black"
                VerticalOptions="Center">
                <Label.GestureRecognizers>
                    <TapGestureRecognizer Command="{x:Binding PasswordVisibilityCommand}" CommandParameter="{x:Binding .}"/>
                </Label.GestureRecognizers>
            </Label>
        </Grid>
    </Border>
</ContentView>

using System.Windows.Input;
namespace TalkMe.Controls;
public partial class CustomEntry : ContentView {
    public CustomEntry() {
        InitializeComponent();
    }
    public static readonly BindableProperty IconFontProperty = BindableProperty.Create(
        nameof(IconFont), typeof(string), typeof(CustomEntry));
    public string IconFont {
        get => (string)GetValue(IconFontProperty);
        set => SetValue(IconFontProperty, value);
    }
    public static readonly BindableProperty PlaceholderTextProperty = BindableProperty.Create(
        nameof(PlaceholderText), typeof(string), typeof(CustomEntry));
    public string PlaceholderText {
        get => (string)GetValue(PlaceholderTextProperty);
        set => SetValue(PlaceholderTextProperty, value);
    }
    public static readonly BindableProperty IsPasswordProperty = BindableProperty.Create(
        nameof(IsPassword), typeof(bool), typeof(CustomEntry));
    public bool IsPassword {
        get => (bool)GetValue(IsPasswordProperty);
        set => SetValue(IsPasswordProperty, value);
    }
    public static readonly BindableProperty PaswordVisibleIconProperty = BindableProperty.Create(
        nameof(PaswordVisibleIcon), typeof(string), typeof(CustomEntry));
    public string PaswordVisibleIcon {
        get => (string)GetValue(PaswordVisibleIconProperty);
        set => SetValue(PaswordVisibleIconProperty, value);
    }
    public static readonly BindableProperty PasswordVisibilityCommandProperty = BindableProperty.Create(
        nameof(PasswordVisibilityCommand), typeof(ICommand), typeof(CustomEntry));
    public string PasswordVisibilityCommand {
        get => (string)GetValue(PasswordVisibilityCommandProperty);
        set => SetValue(PasswordVisibilityCommandProperty, value);
    }
}

Eduardo Gomez Romero 1,375 Reputation points

2024-11-12T03:19:08.03+00:00

I tried to erase my Custom Control from the login screen, and it works, what I am doing wrong?
Eduardo Gomez Romero 1,375 Reputation points

2024-11-12T03:29:45.4266667+00:00

I fixed it, I out that I was declaring a command, but I returned a string
Yonglun Liu (Shanghai Wicresoft Co,.Ltd.) 50,166 Reputation points Microsoft External Staff

2024-11-12T05:27:19.3033333+00:00

Thanks for your feedback.

May I know whether your issue has been solved or not? If you're still having problems, please explain in detail what is still going wrong and what you need help with.

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