Question

In MVVM it is normal to connect View to the ViewModel with data binding.

Therefore if the name of a properties changes on one of the Model objects that is databound to there is no compiler error.

When the compiler will not stop a bug, the next thing I think of is “UnitTest”, However

How do you unit test this without
spending forever writing a GUI test?

Is there a system that will check that all the properties that are bound to is valid, (without having to run the UI) that I can call in a unit test?

I am looking for something that will take the view, and then loop over all WPF controls, for each WPF control it will look at all the binding and check if they are valid.

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By the way there have been a few good questions about how to make OnPropertyChanged safe, and/or how to test it (But done of these get down to the level of a WPF view.)

• How to make Databinding type safe and support refactoring
• Automatically INotifyPropertyChanged
• workarounds for nameof() operator in C#: typesafe databinding
• A Fluent Interface For Testing INotifyPropertyChanged
• Automatic Class Tester will test all simple proptites and INotifyPropertyChanged

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I have put a bounty on this question, as someone must have thought hard about the problem and come up with soltions.

Answer 1

I think I’ve come up with something that may work using simple reflection, and adapting some code I’ve used in the past (the code for the FindBindingsRecursively method was written by Martin Bennedik’s as part of his Enterprise WPF Validation Control):

[TestMethod]
public void CheckWpfBindingsAreValid()
{
    // instansiate the xaml view and set DataContext
    var yourView = new YourView(); 
    yourView.DataContext = YourViewModel;

    FindBindingsRecursively(yourView,
            delegate(FrameworkElement element, Binding binding, DependencyProperty dp)
            {
                var type = yourView.DataContext.GetType();

                // check that each part of binding valid via reflection
                foreach (string prop in binding.Path.Path.Split('.'))
                {
                    PropertyInfo info = type.GetProperty(prop);
                    Assert.IsNotNull(info);
                    type = info.PropertyType;
                }
    });
}

private delegate void FoundBindingCallbackDelegate(FrameworkElement element, Binding binding, DependencyProperty dp);

private void FindBindingsRecursively(DependencyObject element, FoundBindingCallbackDelegate callbackDelegate)
{
    // See if we should display the errors on this element
    MemberInfo[] members = element.GetType().GetMembers(BindingFlags.Static |
                BindingFlags.Public |
                BindingFlags.FlattenHierarchy);

    foreach (MemberInfo member in members)
    {
        DependencyProperty dp = null;

        // Check to see if the field or property we were given is a dependency property
        if (member.MemberType == MemberTypes.Field)
        {
            FieldInfo field = (FieldInfo)member;
            if (typeof(DependencyProperty).IsAssignableFrom(field.FieldType))
            {
                dp = (DependencyProperty)field.GetValue(element);
            }
        }
        else if (member.MemberType == MemberTypes.Property)
        {
            PropertyInfo prop = (PropertyInfo)member;
            if (typeof(DependencyProperty).IsAssignableFrom(prop.PropertyType))
            {
                dp = (DependencyProperty)prop.GetValue(element, null);
            }
        }

        if (dp != null)
        {
            // Awesome, we have a dependency property. does it have a binding? If yes, is it bound to the property we're interested in?
            Binding bb = BindingOperations.GetBinding(element, dp);
            if (bb != null)
            {
                // This element has a DependencyProperty that we know of that is bound to the property we're interested in. 
                // Now we just tell the callback and the caller will handle it.
                if (element is FrameworkElement)
                {
                    callbackDelegate((FrameworkElement)element, bb, dp);
                }
            }
        }
    }

    // Now, recurse through any child elements
    if (element is FrameworkElement || element is FrameworkContentElement)
    {
        foreach (object childElement in LogicalTreeHelper.GetChildren(element))
        {
            if (childElement is DependencyObject)
            {
                FindBindingsRecursively((DependencyObject)childElement, callbackDelegate);
            }
        }
    }
}