Question

I am trying to setup a custom attribute in C# to set whether a business object property is editable, eventually enabling or disabling ReadOnly a textbox in XAML. Since (I thought) IsEditable was already implemented in System.Windows.Controls, i thought this would work:

[AttributeUsage(AttributeTargets.Property)]
public class EditableAttribute : Attribute
{
    public EditableAttribute(bool isEditable)
    {
        this.ReadOnly = !isEditable;

    }
    public virtual bool ReadOnly { get; set; }
}

Well, go figure, it doesn’t. I set [Editable(false)] to a string in an object and it is still editable. I have a feeling I’m not even close. Any help or suggestions would be greatly appreciated!

I am aware this can be setup as a style in xaml, but for this case it needs to be in the business object.

Thanks

Answer 1

You can use BindingDecoratorBase to use custom binding and use an attribute.

The following code is just me modifying my code in my project that uses custom validation . It probably should be refractored.

public interface IEditatble
{
    void SetValue(Control sender, DependencyProperty property);
}

[AttributeUsage(AttributeTargets.Property)]
public class EditableAttribute : Attribute, IEditatble
{
    public EditableAttribute(bool isEditable)
    {
        this.ReadOnly = !isEditable;

    }
    public virtual bool ReadOnly { get; set; }

    public void SetValue(System.Windows.Controls.Control sender, System.Windows.DependencyProperty property)
    {
        sender.SetValue(property, this.ReadOnly);
    }
}

You can create a custom binding:

 public class ReadonlyBinding : BindingDecoratorBase
 {
    private DependencyProperty _targetProperty = null;
    public ReadonlyBinding()
    : base()
    {
        Binding.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
    }

    public override object ProvideValue(IServiceProvider provider)
    {
        // Get the binding expression
        object bindingExpression = base.ProvideValue(provider);

        // Bound items
        DependencyObject targetObject;
       
        // Try to get the bound items
        if (TryGetTargetItems(provider, out targetObject, out _targetProperty))
        {
            if (targetObject is FrameworkElement)
            {
                // Get the element and implement datacontext changes
                FrameworkElement element = targetObject as FrameworkElement;
                element.DataContextChanged += new DependencyPropertyChangedEventHandler(element_DataContextChanged);
            }
        }

        // Go on with the flow
        return bindingExpression;
    }

    void element_DataContextChanged(object sender, DependencyPropertyChangedEventArgs e)
    {
        object datacontext = e.NewValue;
        if (datacontext != null && _targetProperty != null)
        {
            PropertyInfo property = datacontext.GetType().GetProperty(Binding.Path.Path);
            if (property != null)
            {
                var attribute = property.GetCustomAttributes(true).Where(o => o is IEditatble).FirstOrDefault();
                if (attribute != null)
                {                        
                    Control cntrl = sender as Control;
                    ((IEditatble)attribute).SetValue(cntrl, _targetProperty);
                }

            }
        }
    }
}

And you can use it like:

[Editable(true)]
public string Name { get; set; }

Xaml:

<TextBox  IsReadOnly="{local:ReadonlyBinding Path=Name}" />