WPF MVVM light Relaycommand can execute not trigger when field value changed - Stack Overflow

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I am using MVVM light (GalaSoft.MvvmLight) in my WPF application.

My View

<base:BaseWindow x:Class="Hub.Kiosk.View.WindowLogin"
        xmlns=";
        xmlns:x=";
        xmlns:d=";
        xmlns:mc=";
        xmlns:local="clr-namespace:Hub.Kiosk.View"
        xmlns:base="clr-namespace:Hub.KIOSK.Base"
        mc:Ignorable="d"
        Title="WindowLogin" Height="450" Width="800">
    <Grid>
        <StackPanel VerticalAlignment="Center" HorizontalAlignment="Center" Orientation="Vertical">
            <TextBlock Text="User Name"/>
            <TextBox Text="{Binding User.UserName, Mode=TwoWay}" Height="30" Width="200" Style="{StaticResource TextBox-Rounded }"/>
            <TextBlock Text="Password"/>
            <TextBox Text="{Binding User.Password, Mode=TwoWay}" Height="30" Width="200" Style="{StaticResource TextBox-Rounded }"/>
            <Rectangle Height="20"/>
            <Button Content="Login" Command="{Binding LoginCommand}"/>
        </StackPanel>
        
    </Grid>
</base:BaseWindow>

ViewModel

public class WindowLoginViewModel : ViewModelBase
{
    private User _user;
    public User User
    {
        get => _user;
        set => Set(ref _user, value);
    }
    #region COMMANDS
    public RelayCommand LoginCommand { get; private set; }
    #endregion
    public WindowLoginViewModel()
    {
        User =new User();
        // Initialize RelayCommand
        LoginCommand = new RelayCommand(LoginProcess, CanLogin);
    }
    private bool CanLogin()
    {           
        return !string.IsNullOrEmpty(User.UserName)
        && !string.IsNullOrEmpty(User.Password);
    }
    private void LoginProcess()
    {
        Console.WriteLine($"Username: {User.UserName} | Password: {User.Password}");
    }
}

Model

public class User : ObservableObject
{
    private string _userName;
    private string _password;

    public string UserName
    {
        get { return _userName; }
        set => Set(ref _userName, value);
    }
    public string Password
    {
        get => _password;
        set => Set(ref _password, value);
    }
}

I need to enable the Login button, when user entered both username & password.

private bool CanLogin()
{           
    return !string.IsNullOrEmpty(User.UserName)
    && !string.IsNullOrEmpty(User.Password);
}

But this CanLogin only fired at the time of loading, after that when I changed value in the textbox, it is not trigger. I'm using .Net Framework 4.5.2 & galasoft mvvm light.

I tried with a simple string field called Comment.

<TextBlock Text="Comment"/>
<TextBox Text="{Binding Comment, Mode=TwoWay}" Height="30" Width="200" Style="{StaticResource TextBox-Rounded }"/>

ViewModel

private string _comment;
public string Comment
{
    get => _comment;
    set => Set(ref _comment, value);
}
private bool CanLogin()
{
    //return !string.IsNullOrEmpty(User.UserName)
    //&& !string.IsNullOrEmpty(User.Password);
    return !string.IsNullOrEmpty(Comment);
}

Still same issue. If I hard code CanLogin as return true, then when LoginProcess fired getting newly entered username & password.

if I set like below, working

public string Comment
{
    get => _comment;
    set
    {
        if (Comment != value)
        {
            _comment = value;
            RaisePropertyChanged();  // Notify UI
            LoginCommand.RaiseCanExecuteChanged();  // Re-check CanExecute
        }
    }
}

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