Realtime validtion

Question

Hello, I am trying to validate a form and enable/disable a button

as you can see I am receiving my values

[AddINotifyPropertyChangedInterface]  
    public class LoginPageViewModel {  
  
        public ICommand OpenRegisterPopupCommand { get; set; }  
  
        public ICommand Register { get; set; }  
  
        public ICommand Login { get; set; }  
  
        public Users Users { get; set; }  
  
        public bool IsPopUpOpen { get; set; }  
  
        public LoginPageViewModel() {  
  
            Users = new Users();  
  
            Login = new Command(LoginAction, LoginAllowd);  
  
            Register = new Command(RegisterAction);  
  
            OpenRegisterPopupCommand = new Command(() => {  
                IsPopUpOpen = true;  
            });  
        }  
  
        private bool LoginAllowd() {  
           return !string.IsNullOrEmpty(Users.Email) && !string.IsNullOrEmpty(Users.Password);  
        }  
  
        private void LoginAction() {  
            throw new NotImplementedException();  
        }  

   <Grid  
            Padding="20"  
            x:DataType="vm:LoginPageViewModel"  
            RowDefinitions="120,Auto,*"  
            RowSpacing="20"  
            VerticalOptions="Center">  
  
            <ffimageloadingsvg:SvgCachedImage  
                HeightRequest="120"  
                Source="book.svg"  
                WidthRequest="120" />  
  
            <Frame  
                Grid.Row="1"  
                Padding="0"  
                BorderColor="Silver"  
                IsClippedToBounds="True"  
                VerticalOptions="FillAndExpand">  
                <StackLayout Padding="20">  
                    <Entry  
                        Placeholder="Email"  
                        Style="{StaticResource EntrySyle}"  
                        Text="{Binding Users.Email}" />  
  
                    <Entry  
                        Placeholder="Password"  
                        Style="{StaticResource EntrySyle}"  
                        Text="{Binding Users.Password}" />  
  
                    <Button Command="{Binding Login}" Text="Login"/>  
                </StackLayout>  
            </Frame>  
  
            <Label  
                Grid.Row="2"  
                HorizontalOptions="End"  
                Style="{StaticResource SignUpLabelStyle}"  
                Text="Do not ave an account? Sign up">  
                <Label.GestureRecognizers>  
                    <TapGestureRecognizer Command="{Binding OpenRegisterPopupCommand}" />  
                </Label.GestureRecognizers>  
            </Label>  
        </Grid>  
    </ScrollView>  


  [AddINotifyPropertyChangedInterface]  
    public class Users {  
        public string Id { get; set; }  
  
        public string Email { get; set; }  
  
        public string Password { get; set; }  
    }  
}  

Because I inject fody, I can see that my value gets an update as I type

By the way, in my ViewModel can see that the Users object is modified, so I do not understand

Answer 1

Here is MainPage.xaml.

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" 
             xmlns:vm="clr-namespace:App142"
             x:Class="App142.MainPage">

    <StackLayout>


        <Grid
             Padding="20"

             RowDefinitions="120,Auto,*"
             RowSpacing="20"
             VerticalOptions="Center">


            <Frame
                 Grid.Row="1"
                 Padding="0"
                 BorderColor="Silver"
                 IsClippedToBounds="True"
                 VerticalOptions="FillAndExpand">
                <StackLayout Padding="20">
                    <Entry
                         Placeholder="Email"

                         Text="{Binding Users.Email}" />

                    <Entry
                         Placeholder="Password"

                         Text="{Binding Users.Password}" />

                    <Button Command="{Binding Login}" Text="Login"/>
                </StackLayout>
            </Frame>

            <Label
                 Grid.Row="2"
                 HorizontalOptions="End"

                 Text="Do not ave an account? Sign up">
                <Label.GestureRecognizers>
                    <TapGestureRecognizer Command="{Binding OpenRegisterPopupCommand}" />
                </Label.GestureRecognizers>
            </Label>
        </Grid>
    </StackLayout>

</ContentPage>

Here is MainPage.xaml.cs. Contains ViewModel and User model.

using PropertyChanged;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;
using Xamarin.Forms;

namespace App142
{
    public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();

            BindingContext = new LoginPageViewModel();
        }


    }
    [AddINotifyPropertyChangedInterface]
    public class LoginPageViewModel
    {



        public ICommand OpenRegisterPopupCommand { get; set; }

        public ICommand Register { get; set; }

        public ICommand Login { get; set; }

        public Users Users { get; set; }

        public bool IsPopUpOpen { get; set; }

        public LoginPageViewModel()
        {

            Users = new Users();
            Users.PropertyChanged += OnUserEditPropertyChanged;
            Login = new Command(LoginAction, LoginAllowd);

            Register = new Command(RegisterAction);

            OpenRegisterPopupCommand = new Command(() => {
                IsPopUpOpen = true;
            });
        }



        void OnUserEditPropertyChanged(object sender, PropertyChangedEventArgs args)
        {
            (Login as Command).ChangeCanExecute();
        }
        private bool LoginAllowd()
        {
            return !string.IsNullOrEmpty(Users.Email) && !string.IsNullOrEmpty(Users.Password);
        }

        private void LoginAction()
        {

        }
        private void RegisterAction()
        {

        }


    }
    [AddINotifyPropertyChangedInterface]
    public class Users: INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        public string Id { get; set; }

        public string Email { get; set; }

        public string Password { get; set; }
    }


}

Answer 2

Hello,​

Welcome to our Microsoft Q&A platform!

You can add Users.PropertyChanged += OnUserEditPropertyChanged; below Users = new Users();, then add OnUserEditPropertyChanged method in your LoginPageViewModel.cs

   void OnUserEditPropertyChanged(object sender, PropertyChangedEventArgs args)  
           {  
               (Login as Command).ChangeCanExecute();  
           }  

When you user‘s property be changed, LoginAllowd method will be executed to judge the value is !string.IsNullOrEmpty(Users.Email) && !string.IsNullOrEmpty(Users.Password);

For more information about Command, you can refer to this thread:
https://learn.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/data-binding/commanding#basic-commanding

Best Regards,

Leon Lu

---

If the response is helpful, please click "Accept Answer" and upvote it.

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.