Property Grid Aggregate Object and ICustomTypeDescriptor

Hello,

I'm trying to use an aggegate object which contains two objects and using the ICustomTypeDescriptor I would like to expose all the properties from both containined objects in a single aggegated object. So, I've implemented this aggregated object as follow :

public class Aggregated : ICustomTypeDescriptor
{
    readonly Object _main;
    readonly Object _extended;
    public Aggregated(Object main, Object extended)
    {
        _main = main;
        _extended = extended;
    }

    public Object Main
    {
        get { return _main; }
    }

    public Object Extended
    {
        get { return _extended; }
    }

    #region ICustomTypeDescriptor implementation

    AttributeCollection ICustomTypeDescriptor.GetAttributes()
    {
        return TypeDescriptor.GetAttributes(Main, true);
    }

    string ICustomTypeDescriptor.GetClassName()
    {
        return TypeDescriptor.GetClassName(Main, true);
    }

    string ICustomTypeDescriptor.GetComponentName()
    {
        return TypeDescriptor.GetComponentName(Main, true);
    }

    TypeConverter ICustomTypeDescriptor.GetConverter()
    {
        return TypeDescriptor.GetConverter(Main, true);
    }

    EventDescriptor ICustomTypeDescriptor.GetDefaultEvent()
    {
        return TypeDescriptor.GetDefaultEvent(Main, true);
    }

    PropertyDescriptor ICustomTypeDescriptor.GetDefaultProperty()
    {
        return TypeDescriptor.GetDefaultProperty(Main, true);
    }

    object ICustomTypeDescriptor.GetEditor(Type editorBaseType)
    {
        return TypeDescriptor.GetEditor(Main, editorBaseType, true);
    }

    EventDescriptorCollection ICustomTypeDescriptor.GetEvents(Attribute[] attributes)
    {
        return TypeDescriptor.GetEvents(Main, attributes, true);
    }

    EventDescriptorCollection ICustomTypeDescriptor.GetEvents()
    {
        return TypeDescriptor.GetEvents(Main, true);
    }

    PropertyDescriptorCollection propsAttribute1;
    PropertyDescriptorCollection propsAttribute2;
    PropertyDescriptorCollection retAttributes;
    PropertyDescriptorCollection props1;
    PropertyDescriptorCollection props2;
    PropertyDescriptorCollection ret;

    PropertyDescriptorCollection ICustomTypeDescriptor.GetProperties(Attribute[] attributes)
    {
        if (retAttributes != null)
            return retAttributes;

        propsAttribute1 = TypeDescriptor.GetProperties(Main, attributes, true);
        propsAttribute2 = TypeDescriptor.GetProperties(Extended, attributes, true);

        retAttributes = new PropertyDescriptorCollection(null);
        foreach (PropertyDescriptor prop in propsAttribute1)
            retAttributes.Add(prop);
        foreach (PropertyDescriptor prop in propsAttribute2)
            retAttributes.Add(prop);
        return retAttributes;
    }

    PropertyDescriptorCollection ICustomTypeDescriptor.GetProperties()
    {
        if (ret != null)
            return ret;
        props1 = TypeDescriptor.GetProperties(Main, true);
        props2 = TypeDescriptor.GetProperties(Extended, true);

        ret = new PropertyDescriptorCollection(null);
        foreach (PropertyDescriptor prop in props1)
            ret.Add(prop);
        foreach (PropertyDescriptor prop in props2)
            ret.Add(prop);
        return ret;
    }

    object ICustomTypeDescriptor.GetPropertyOwner(PropertyDescriptor pd)
    {
        if (props1.Contains(pd) || propsAttribute1.Contains(pd))
            return Main;
        if (props2.Contains(pd) || propsAttribute2.Contains(pd))
            return Extended;
        return Main;
    }

Using this aggregate class I get the following exception :

Unable to cast object of type 'PropertyControl.ComponentService.Aggregated' to type 'System.Windows.DependencyObject'.

call stack :

at MS.Internal.ComponentModel.DependencyObjectPropertyDescriptor.FromObj(Object value) at MS.Internal.ComponentModel.DependencyObjectPropertyDescriptor.GetValue(Object component) at #ZC.#0C.getValue() at Mindscape.WpfElements.PropertyEditing.Many1.GetValue(T& value, Boolean& isConsistent) at Mindscape.WpfElements.PropertyEditing.Many1.#SV() at Mindscape.WpfElements.PropertyEditing.Many.#LV(Type type, IList`1 properties, #pD descriptor) at Mindscape.WpfElements.PropertyEditing.MultipleObjectWrapper.GetValue(#pD property) at #ZC.#pD.GetValue(Object component) at #ZC.#Vl.GetValue(Object obj, BindingFlags invokeAttr, Binder binder, Object[] index, CultureInfo culture) at Mindscape.WpfElements.PropertyEditing.PropertyNode.getValue() at Mindscape.WpfElements.PropertyEditing.BuiltInEditor.#3(Node node, Boolean editable, Boolean& allowExpand) at Mindscape.WpfElements.PropertyEditing.BuiltInEditor.GetEditSettings(Node node) at Mindscape.WpfElements.PropertyEditing.BuiltInEditor.CanEdit(Node node) at Mindscape.WpfElements.PropertyEditing.ObjectWrappingEditor.BuildTemplate(Node node) at Mindscape.WpfElements.PropertyEditing.EditorSelector.SelectTemplate(Object item, DependencyObject container) at System.Windows.Controls.ContentPresenter.ChooseTemplate() at System.Windows.Controls.ContentPresenter.EnsureTemplate() at System.Windows.Controls.ContentPresenter.OnPreApplyTemplate() at System.Windows.FrameworkElement.ApplyTemplate() at System.Windows.FrameworkElement.MeasureCore(Size availableSize) at System.Windows.UIElement.Measure(Size availableSize) at System.Windows.ContextLayoutManager.UpdateLayout() at System.Windows.ContextLayoutManager.UpdateLayoutCallback(Object arg) at System.Windows.Media.MediaContext.FireInvokeOnRenderCallbacks() at System.Windows.Media.MediaContext.RenderMessageHandlerCore(Object resizedCompositionTarget) at System.Windows.Media.MediaContext.RenderMessageHandler(Object resizedCompositionTarget) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs) at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.DispatcherOperation.InvokeImpl() at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Windows.Threading.DispatcherOperation.Invoke() at System.Windows.Threading.Dispatcher.ProcessQueue() at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs) at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs) at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam) at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg) at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame) at System.Windows.Application.RunInternal(Window window) at System.Windows.Application.Run() at UFSolution.Startup.Main(String[] args) in e:\Documents\Visual Studio 2010\Projects\UFSolution\UFSolution\Startup.cs:line 166 at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args) at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly() at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart()

the Main contained object is a WPF FrameworkElement, but the implementation for ICustomTypeDescriptor.GetPropertyOwner(PropertyDescriptor pd) is never called for the WPF frameworkElement properties. Can you please check if there is a workaround ?

thanks

I've prepared an example based on the propertygridcustomization sample. It's attached here.

If I use the Aggeegated object with normal classes there is no problem and it works if I use the Aggregated object with a DependencyObject than an exception is thrown

you can try the sample comment and uncomment the sample lines :

  // var aggregated = new Aggregated(Pet.Dinah, Person.AliceFull);
  var aggregated = new Aggregated(this, Person.AliceFull);

I've found a workaound declaring the aggregated class as :

public class Aggregated : DependencyObject, ICustomTypeDescriptor

Hello

Thanks for all the information about this scenario. I've improved the property grid to check the GetPropertyOwner method when dealing with dependency objects. This improvement will be available in the next nightly build. This will mean you won't need your custom type descriptor to extend DependencyObject.

Jason Fauchelle

Hello Jason,

thanks,

I've tried the nightly build and it works, now I have a problem with multiple selection. To reproduce this problem just edit the 01GettingStarted method in the sample I've attached before as follow :

public _01_GettingStarted()
{
  InitializeComponent();

  // var aggregated = new Aggregated(Pet.Dinah, Person.AliceFull);
  var aggregated1 = new Aggregated(this, Person.AliceFull);
  var aggregated2 = new Aggregated(this, Person.AliceFull);
  var list = new List<Aggregated>();
    list.Add(aggregated1);
    list.Add(aggregated2);
    PropertyGrid.SelectedObjects = list;
}

you should get the exception

thanks

Thanks for pointing out this other scenario.

This will be resolved in the next nightly build.

Jason Fauchelle

ok Jason, thank you,

I'm attaching another sample which throws a null reference exception. This time the scenario is using an ExpandoObject

please let me know

thank you

The PropertyGrid did not previously support ExpandoObject.

I've added some initial support for this to at least avoid the start-up exception. This will be available in the next nightly build. I have not played around with ExpandoObject much yet, so this may not be fully functional, but it's a start. Let me know how it goes.

-Jason Fauchelle