Login MVVM / Labels - xamarin

Question

i have a question regarding to Binding. I have a Login that I now decided to transfer to MVVM until now i had labels with content "wrong password" and such in code behind and i was setting their visibility. Btw I do have RESX file and I am binding my labels, just not sure how to approach this.
bool isPreparedToBeSubmitted = true;
if (string.IsNullOrEmpty(UserName))
{
isPreparedToBeSubmitted = false;
emailValLabel.IsVisible = true;
}
if (string.IsNullOrEmpty(Password))
{
isPreparedToBeSubmitted = false;
passwordEntryValLabel.IsVisible = true;
}
But I think this can be done much nicer, but I am not sure how. Do i get the visibility bool in Model and then set binding to the label in View?

Answer 1

Since you want to use MVVM. It would be better to bind the text of entry to ViewModel . Don't forget to set the binding mode as OneWayToSource .
You could check the following demo . The page contains two entries . The submit button will appear when user both input the user name and password .
in xaml
<StackLayout VerticalOptions="CenterAndExpand" HorizontalOptions="CenterAndExpand">
<Entry Placeholder="input username" Text="{Binding UserName,Mode=OneWayToSource}" HeightRequest="40" WidthRequest="200" />
<Entry Placeholder="input password" Text="{Binding Password,Mode=OneWayToSource}" HeightRequest="40" WidthRequest="200" />
<Button Text="Submit" IsVisible="{Binding IsVisible}" Command="{Binding SubmitCommand}" />
</StackLayout>
in ViewModel
public class MyViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
public ICommand SubmitCommand { get; set; }
//IsVisible
bool isVisible;
public bool IsVisible
{
get
{
return isVisible;
}
set
{
if (isVisible != value)
{
isVisible = value;
NotifyPropertyChanged("IsVisible");
}
}
}
string userName;
public string UserName
{
get
{
return userName;
}
set
{
if (userName != value)
{
userName = value;
IsSubmitVisible();
NotifyPropertyChanged("UserName");
}
}
}
string password;
public string Password
{
get
{
return password;
}
set
{
if (password != value)
{
password = value;
IsSubmitVisible();
NotifyPropertyChanged("Password");
}
}
}
void IsSubmitVisible()
{
if (!string.IsNullOrEmpty(UserName) && !string.IsNullOrEmpty(Password))
{
IsVisible = true;
}
else
{
IsVisible = false;
}
}
public MyViewModel()
{
SubmitCommand = new Command(()=> {
//...
});
}
}