Question

For some reason I’m having issues Binding a custom User Control up through my ViewModel in an MVVM WPF application. The basic control is a Date entry form with three text boxes. I am using the codebehind for the usercontrol to capture the textchange event and so some manipulation. For some reason Adding Binding to the property never triggers.

XAML of user Control:

<UserControl x:Class='MYLibray.DateBox' xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation' xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml' Height='300' Width='800'> <StackPanel>      <Border CornerRadius='10' Height='200' BorderBrush='Gray' Background='Gray'>     <StackPanel Orientation='Horizontal' OpacityMask='{x:Null}' HorizontalAlignment='Center'>     <TextBox Name='txtMonth' Height='100' Width='90' BorderThickness='0,0,0,5' Background='{x:Null}' Text='' FontSize='72' TextChanged='TextChanged'>         <TextBox.BorderBrush>             <LinearGradientBrush EndPoint='0.5,1' StartPoint='0.5,0'>                 <GradientStop Color='#FF000000' Offset='0'/>                 <GradientStop Color='#FF000000' Offset='1'/>             </LinearGradientBrush>         </TextBox.BorderBrush>     </TextBox>             <TextBlock Text='/' FontSize='72' Height='100' Width='50' />             <TextBox x:Name='txtDay' Height='100' Width='90' Background='{x:Null}' BorderThickness='0,0,0,5' VerticalAlignment='Stretch' FontSize='72' TextChanged='TextChanged'>                 <TextBox.BorderBrush>                     <LinearGradientBrush EndPoint='0.5,1' StartPoint='0.5,0'>                         <GradientStop Color='#FF000000' Offset='0'/>                         <GradientStop Color='#FF000000' Offset='1'/>                     </LinearGradientBrush>                 </TextBox.BorderBrush>             </TextBox>             <TextBlock Text='/19' FontSize='72' Height='100' Width='Auto' />             <TextBox x:Name='txtYear' Height='100' Width='90' Background='{x:Null}' BorderThickness='0,0,0,5'  FontSize='72' TextChanged='TextChanged'>                 <TextBox.BorderBrush>                     <LinearGradientBrush EndPoint='0.5,1' StartPoint='0.5,0'>                         <GradientStop Color='#FF000000' Offset='0'/>                         <GradientStop Color='#FF000000' Offset='1'/>                     </LinearGradientBrush>                 </TextBox.BorderBrush>             </TextBox>     </StackPanel>     </Border>  </StackPanel> 

CodeBehind:

public partial class DateBox : UserControl 

{

  private string _date = '';   public static DependencyProperty TextProperty = DependencyProperty.RegisterAttached('DateText', typeof(string), typeof(DateBox), new PropertyMetadata(TextPropertyChanged));   public static DependencyProperty EnabledProperty = DependencyProperty.RegisterAttached('Enabled', typeof(bool), typeof(DateBox), null);    public DateBox()   {                                       InitializeComponent();      this.DataContext = this;      txtMonth.Focus();   }    public bool Enabled   {      get      {         return (bool)GetValue(DateBox.EnabledProperty);      }      set      {         SetValue(DateBox.EnabledProperty, value);          txtDay.IsEnabled = value;         txtMonth.IsEnabled = value;         txtYear.IsEnabled = value;      }   }    public string DateText   {      get      {         return (string)this.GetValue(TextProperty);      }      set      {         this.SetValue(TextProperty, value);      }   }    static void TextPropertyChanged(DependencyObject property,DependencyPropertyChangedEventArgs args)   {      ((DateBox)property).OnTextPropertyChanged((object)args.NewValue);   }    private void OnTextPropertyChanged(object newValue)   {      _date = newValue.ToString();      this.UpdateLayout();      DateTime d;      if (DateTime.TryParse(_date, out d))      {         txtDay.Text = d.Day.ToString();         txtMonth.Text = d.Month.ToString();         txtYear.Text = (d.Year - 1900).ToString();      }      else      {         txtDay.Text = '';         txtMonth.Text = '';         txtYear.Text = '';      }       DateText = d.ToShortDateString();   }    bool AreAllValidNumericChars(string str)   {      bool ret = true;      if (str == System.Globalization.NumberFormatInfo.CurrentInfo.PositiveSign)      {         return ret;      }      int l = str.Length;      for (int i = 0; i < l; i++)      {         char ch = str[i];         ret &= Char.IsDigit(ch);      }       return ret;   }    private void TextChanged(object sender, TextChangedEventArgs e)   {       TextBox txt = (TextBox)sender;       switch (txt.Name)      {         case 'txtMonth':            if (txt.Text.Length == 1)            {               if (Convert.ToInt32(txt.Text) > 1)               {                  string value = txt.Text;                  txt.Text = '0' + value;                  txtDay.Focus();               }            }            if (txt.Text.Length == 2)            {               txtDay.Focus();            }            break;         case 'txtDay':            if (txt.Text.Length == 1)            {               if (Convert.ToInt32(txt.Text) > 3)               {                  string value = txt.Text;                  txt.Text = '0' + value;                  txtYear.Focus();               }            }            if (txt.Text.Length == 2)            {               txtYear.Focus();            }            break;          case 'txtYear':            if (txt.Text.Length == 2)            {               DateTime d;               string datestring = txtMonth.Text + '/' + txtDay.Text + '/19' + txtYear.Text;               if (DateTime.TryParse(datestring,out d))               {                  DateText = d.ToShortDateString();               }            }            break;         default:            break;      }   } 

}

When I create the usercontrol in the DataTemplate like so:

<uc:DateBox DateText='{Binding BirthDate}' /> 

The get and set of BirthDate in my ViewModel never get set. BirthDate on the VM is a String.

Answer 1

Check the DataContext of the control and of the parent.

to help with debugging your bindings, check out Bea Stollnitz’s blog

basically, add this xmlns to your control

xmlns:diagnostics='clr-namespace:System.Diagnostics;assembly=WindowsBase' 

then add this to your Binding(s)

{Binding ....    , diagnostics:PresentationTraceSources.TraceLevel=High }