Question

I have :

 public class Person : INotifyPropertyChanged
    {
       private string _name;

        public int Age { get; set; }

        public string Name
        {
            get { return _name; }
            set
            {
                if (!String.IsNullOrEmpty(_name))
                {
                    if (String.IsNullOrEmpty(value))
                    { 
                       throw new Exception("name couldn't be null");



                    }
                    else if ((_name.Equals(value) != true))
                    {
                        if (!String.IsNullOrEmpty(value))
                        {
                            throw new Exception("name couldn't be null");
                        }
                        else
                        {
                            InvokePropertyChanged("_name");
                        }


                        _name = value;
                    }

                }

                else if (String.IsNullOrEmpty(value))
                {
                    throw new Exception("name couldn't be null");
                }
                else
                {
                    _name = value;
                }

            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        private void InvokePropertyChanged(string propertyName)
        {

            var e = new PropertyChangedEventArgs(propertyName);

            PropertyChangedEventHandler changed = PropertyChanged;

            if (changed != null) changed(this, e);

        }

>
<Grid>
    <StackPanel>
        <TextBox Name="tbName" Text="{Binding Path=Name, Mode=TwoWay}"></TextBox>
        <TextBox Name="tbOther" Text="Come in"></TextBox>
    </StackPanel>
</Grid>

and

 public UserControl1()
        {
            InitializeComponent();

            Person person = new Person();
            person.Name = "Patrick";

 this.DataContext = person;

        }

Why when I debug and enter to line of :

throw new Exception(“name couldn’t be null”);

exception is not showing.

Answer 1

I think you want to assign the Person object to the control’s DataContext:

public UserControl1()
{
    InitializeComponent();
    Person person = new Person();
    person.Name = "Patrick";
    this.DataContext = person;
}

You may also want to set ValidatesOnExceptions on your binding so that the UI will display the error template when an exception is thrown in the setter.

<TextBox Name="tbName" Text="{Binding Path=Name, Mode=TwoWay, ValidatesOnExceptions=True}"></TextBox>