Xamarin button not being enabled - xamarin

Question

A User register page has a Save toolbar button. It is always disabled. The CanExecute method is not being called when a parameter is changed on screen. The Save button should be enabled by the CanExecute method when the user name and password are non blank and the PW and confirmpassword fields match. The CanExecute method is not being called when a change is made to any of the three fields.
Why isn't CanExecute method being called for the registerButton when something is entered into any of the three fields (username, PW, and ConfirmPassword ) The OnPropertyChanged method is being called for any change in these three fields, but apparently the external code is not detecting that a change has been made. Is this some kind of scope issue?
The entire project is available if necessary.
Jim Durbin
Here is the xaml code
<?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:d="http://xamarin.com/schemas/2014/forms/design"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
x:Class=*"ButtonTest.RegisterPage"*>
<ContentPage.ToolbarItems>
**<ToolbarItem x:Name="registerButton"
Text="Save"
Command="{Binding RegisterCommand}"
CommandParameter="{Binding Password}"/>**
</ContentPage.ToolbarItems>
<ContentPage.Content>
<ScrollView Orientation="Vertical">
<StackLayout x:Name="containerStackLayout"
VerticalOptions="FillAndExpand"
Margin="20">
<Label Text="Registration"
FontSize="Large"
HorizontalOptions="Center"
FontAttributes="Bold"></Label>
<Entry x:Name="UserName"
Placeholder="User Name"
Text="{Binding UserName, Mode=TwoWay}"
Keyboard="Text"/>
<Entry x:Name="PasswordEntry"
Placeholder="Password"
Text="{Binding PW, Mode=TwoWay}"
IsPassword="True"/>
<Entry x:Name="confirmPasswwordEntry"
Placeholder="Confirm Password"
Text="{Binding ConfirmPassword, Mode=TwoWay}"
IsPassword="True"/>
<Entry x:Name="Email"
Placeholder="Email"
Text="{Binding Email, Mode=TwoWay}"
Keyboard="Email"/>
</StackLayout>
</ScrollView>
</ContentPage.Content>
</ContentPage>
viewModel code
using ButtonTest.Model;
using System.ComponentModel;
using ButtonTest.ViewModel.Commands;
namespace ButtonTest.ViewModel
{
public class RegisterPageVM : INotifyPropertyChanged
{
public RegisterCommand RegisterCommand { get; set; }
private Password user;
public Password User
{
get { return user; }
set
{
user = value;
OnPropertyChanged("User");
}
}
private string username;
public string UserName
{
get { return username; }
set
{
username = value;
User = new Password()
{
UserName = this.UserName,
PW = this.PW,
ConfirmPassword = this.ConfirmPassword
};
OnPropertyChanged("UserName");
}
}
private string pw;
public string PW
{
get { return pw; }
set
{
pw = value;
User = new Password()
{
UserName = this.UserName,
PW = this.PW,
ConfirmPassword = this.ConfirmPassword
};
OnPropertyChanged("PW");
}
}
private string confirmpassword;
public string ConfirmPassword
{
get { return confirmpassword; }
set
{
confirmpassword = value;
User = new Password()
{
UserName = this.UserName,
PW = this.PW,
ConfirmPassword = this.ConfirmPassword
};
OnPropertyChanged("ConfirmPassword");
}
}
public RegisterPageVM()
{
RegisterCommand = new RegisterCommand(this);
//User = new Password();
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
public void Register(Password user)
{
Password.Register(user);
}
}
}
Here is the command code
using System;
using System.Windows.Input;
using ButtonTest.Model;
namespace ButtonTest.ViewModel.Commands
{
public class RegisterCommand : ICommand
{
private RegisterPageVM viewModel;
public RegisterCommand(RegisterPageVM viewModel)
{
this.viewModel = viewModel;
}
public event EventHandler CanExecuteChanged;
public bool CanExecute(object parameter)
{
Password user = (Password)parameter;
if (user != null)
{
if (user.PW == user.ConfirmPassword)
{
if (string.IsNullOrEmpty(user.UserName) || string.IsNullOrEmpty(user.PW))
return false;
return true;
}
return false;
}
return false;
}
public void Execute(object parameter)
{
Password user = (Password)parameter;
viewModel.Register(user);
}
}
}
here is the Password.cs code
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Numerics;
using System.Linq;
using System.Threading.Tasks;
namespace ButtonTest.Model
{
public class Password : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
private string username;
public string UserName
{
get { return username; }
set
{
username = value;
OnPropertyChanged("UserName");
}
}
private string pw;
public string PW
{
get { return pw; }
set
{
pw = value;
OnPropertyChanged("PW");
}
}
private string confirmPassword;
public string ConfirmPassword
{
get { return confirmPassword; }
set
{
confirmPassword = value;
OnPropertyChanged("ConfirmPassword");
}
}
private string email;
public string Email
{
get { return email; }
set { email = value; }
}
public static async void Insert(Password password)
{
await App.client.GetTable<Password>().InsertAsync(password);
//await App.client.SyncContext.PushAsync();
}
public static async Task<bool> Delete(Password password)
{
try
{
await App.passwordsTable.DeleteAsync(password);
//await App.client.SyncContext.PushAsync();
return true;
}
catch (Exception)
{
return false;
}
}
public static async void Register(Password user)
{
await App.client.GetTable<Password>().InsertAsync(user);
}
public static async Task<bool> Login(string username, string password)
{
bool isEmailEmpty = string.IsNullOrEmpty(username);
bool isPasswordEmpty = string.IsNullOrEmpty(password);
if (isEmailEmpty || isPasswordEmpty)
{
return false;
}
else
{
var user = (await App.client.GetTable<Password>().Where(u => u.UserName == username).ToListAsync()).FirstOrDefault();
if (user != null)
{
App.user = user;
if (user.pw == password)
{
return true;
}
else
{
return false;
}
}
else
{
return false;
}
}
}
}
}

Answer 1

This problem is solved. The CommandParameter binding for the RegisterCommand needed to be set to the User property in the VM. The CanExecute method is now being called for each change in the UserName, PW, and ConfirmPassword fields.
It was solved by E.Z. Hart from the github support group. Many thanks for the solution.