cannot set multiple base to custom control error

Question

i'm trying to build a wpf custom control library, want to create some controls that inherited from wpf controls (textBox, label, ...) and i wanted them all to be inherted from a base class and wpf control, here is one of them:

public class MovableTextbox : TextBox, Movable


public class Movable : Control

and it always shows error :
Severity Code Description Project File Line Suppression State
Error CS1721 Class 'MovableTextbox' cannot have multiple base classes: 'TextBox' and 'Movable'

Answer 1

There is a workaround for you to add some custom Dependency Properties for your MovableTextbox which inherited from Textbox. You can create a class which inherit from DependencyObject to declare your custom Dependency Properties and use it like local:className.propertyName in the customControl. I will give you a demo to use it.
Here is the class:

public class RotationManager : DependencyObject
    {
        public static double GetAngle(DependencyObject obj)
        {
            return (double)obj.GetValue(AngleProperty);
        }

        public static void SetAngle(DependencyObject obj, double value)
        {
            obj.SetValue(AngleProperty, value);
        }

        public static readonly DependencyProperty AngleProperty =
            DependencyProperty.RegisterAttached("Angle", typeof(double), typeof(RotationManager), new PropertyMetadata(0.0, OnAngleChanged));

        private static void OnAngleChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
        {
            var element = obj as UIElement;
            if (element != null)
            {
                element.RenderTransformOrigin = new Point(0.5, 0.5);
                element.RenderTransform = new RotateTransform((double)e.NewValue);
            }
        }
    }

The custom control code is:

 public class MyTextBox:TextBox
    {
        private bool m_underLine;
        public bool UnderLine
        {
            get { return m_underLine; }
            set
            {
                if (this.m_underLine != value)
                {
                    if (value)
                    {
                        this.TextDecorations = System.Windows.TextDecorations.Underline;
                    }
                    m_underLine = value;
                }
            }
        }     
    }

You can use it in the custom control like:

<local:MyTextBox UnderLine="True" local:RotationManager.Angle="60" 
                         Width="400" Height="80"
                         Text="This is my custome TextBox"
                         ></local:MyTextBox>