Binding button IsEnabled to a property

Question

I have a class which has implemented INotifyPropertyChanged. This class UserInfo has a boolean variable isuserLoggedIn. Now in my mainform I have buttons whose isEnabled I wish to bind to UserInfo.isuserLoggedIn.

How to do that?

    public  class UserInfo : INotifyPropertyChanged
    {
        private static readonly UserInfo _instance = new UserInfo();
        private string username; 

        private  bool isLoggedIn;

        public string UserName
        {
            get { return username; }
            set
            {
                username = value;
                NotifyPropertyChanged("UserName");
            }
        }

        public  bool UserLoggedIn
        {
            get { return isLoggedIn; }
            set
            {
                isLoggedIn = value;
                NotifyPropertyChanged("UserLoggedIn");
            }
        }


        public  event PropertyChangedEventHandler PropertyChanged;

        public void NotifyPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }               

    public static UserInfo GetUserInfo()
    {
        return _instance;
    }

}

In the main I have:

public class MainWindow
{
    UserInfo currentUser = UserInfo.GetUserInfo();
}

The XAML is:

<Button IsEnabled="{Binding ElementName=currentUser, Path=UserLoggedIn}"/>

Answer 1

You'll need to set the DataContext of your view to an instance of your UserInfo class. And then bind the IsEnabled property of your button to the UserIsLoggedIn boolean property on your UserInfo view model. Here's an example of binding an element's attribute to a property on a corresponding view model: passing a gridview selected item value to a different ViewModel of different Usercontrol

After seeing your edit, you'll again need to set the DataContext of your view to the currentUser object, then remove the ElementName portion of your button's IsEnabled binding expression.

Answer 2

You can bind IsEnabled to Length of the username textbox:

<TextBox Name="usernameTxt" Width="100" Height="30"/>
<Button Content="SomeButton " Width="100" Height="30" 
  IsEnabled="{Binding ElementName=usernameTxt, Path=Text.Length, Mode=OneWay}"></Button>