Question

I have a custom control that I want to style:

It is just a class that inherits from TextBox and another Interface, the interface only adds an extra property.

How can I apply a style to this custom control so that when the read only property is set, the background turns gray?

---

public class DionysusTextBox : TextBox, IDionysusControl
  {

    public DionysusTextBox()
    {
      SetStyle();
    }

    #region IDionysusControl Members

    public bool KeepReadOnlyState
    {
      get { return (bool)GetValue(KeepReadOnlyStateProperty); }
      set { SetValue(KeepReadOnlyStateProperty, value); }
    }

    // Using a DependencyProperty as the backing store for MyProperty.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty KeepReadOnlyStateProperty =
        DependencyProperty.Register("KeepReadOnlyState", typeof(bool), typeof(DionysusTextBox), new UIPropertyMetadata(true));

    #endregion

    #region Style

    Style styleListBoxItem = new Style(typeof(DionysusTextBox));
    Trigger triggerReadonly = new Trigger { Property = DionysusTextBox.IsReadOnlyProperty, Value = true };

    private void SetStyle()
    {
      triggerReadonly.Setters.Add(new Setter(DionysusTextBox.BackgroundProperty, Brushes.Black));
      this.Triggers.Add(triggerReadonly);
    }

    #endregion


  }

---

Above is the code for the entire class, the way I used the style seemed like the appropriate way but when I add this control to the designer I get the following error:

Triggers collection members must be of type EventTrigger.

Can anyone point me in the right direction?

Answer 1

You can redefine dependency properties’ default behavior, and in particular, you can define PropertyChangedCallbacks:

public class DionysusTextBox : TextBox, IDionysusControl
{
    static DionysusTextBox()
    {   
        //For the IsReadOnly dependency property    
        IsReadOnlyProperty.OverrideMetadata(
            //On the type DionysusTextBox
            typeof(DionysusTextBox), 
            //Redefine default behavior           
            new FrameworkPropertyMetadata(
                //Default value, can also omit this parameter
                null,
                //When IsReadOnly changed, this is executed 
                new PropertyChangedCallback(
                    (dpo, dpce) =>
                    {
                       //dpo hold the DionysusTextBox instance on which IsReachOnly changed
                       //dpce.NewValue hold the new value of IsReadOnly

                       //Run logic to set the background here, you are on the UI thread.

                       //Example of setting the BorderBrush from ARGB values:
                       var dioBox = dpo as DionysusTextBox;
                       //Should always be true, of course, it's just my OCD ;)
                       if (dioBox != null)                  
                       {
                          dioBox.BorderBrush = 
                              ColorConverter.ConvertFromString("#FFDDDDDD") as Color?;
                       }
                    })));

        //For the BorderBrush property
        BorderBrushProperty.OverrideMetadata(
            //On the type DionysusTextBox
            typeof(DionysusTextBox), 
            //Redefine default behavior           
            new FrameworkPropertyMetadata(
                //Default value
                ColorConverter.ConvertFromString("#FFDDDDDD") as Color?));
    }


    public DionysusTextBox()
    {
      SetStyle();
    }
}

Please be careful: UIPropertyMetadata != FrameworkPropertyMetadata