Here my xaml file :

<TextBox Height="30" Width="100" Text="{Binding Path=txtName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Margin="346,239,346,150"/>

        <Button Name="Submit" Height="30" Width="100" Content="Submit Me" Command="{Binding submit}" CommandParameter="{Binding Text, ElementName=fName}" Margin="346,185,346,204"/>

        <TextBox Height="30" Width="100" Text="{Binding Path=copyName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Margin="346,135,346,254" />

This is my ViewModel.cs

public event PropertyChangedEventHandler PropertyChanged;

        private string _txtName;

        public string txtName
        {
            get { return _txtName; }
            set {
                _txtName = value;
                OnPropertyChanged("txtName");
                }
            
        }
        private int _copyName;

        public int copyName
        {
            get { return _copyName; }
            set { _copyName = value;
                OnPropertyChanged("copyName");
                }
        }