I am trying to create a subclass of ShapeNode and drag that node onto a diagram. When I do that, I get a null reference exception on the drop. Specifically:

PresentationCore.dll!System.Windows.OleServicesContext.OleDoDragDrop(System.Runt
ime.InteropServices.ComTypes.IDataObject dataObject, MS.Win32.UnsafeNativeMethods.IOleDropSource dropSource, int allowedEffects, int[] finalEffect)

My code is very simple.

public class ShapeNodeTest : ShapeNode {} 

<Window xmlns:diag="xxxx:// mindfusion.eu/diagramming/wpf"  x:Class="CustomInteractive.MainWindow"
xmlns="xxxx://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="xxxx://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:CustomInteractive"
        Title="MainWindow" SizeToContent="WidthAndHeight">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto" />
            <ColumnDefinition />
        </Grid.ColumnDefinitions>
        <diag:NodeListView>
            <diag:ShapeNode Shape="Rectangle" Bounds="0,0,30,30" />
            <local:ShapeNodeTest Shape="Rectangle" Bounds="0,0,40,40" />
        </diag:NodeListView>
        <diag:Diagram Grid.Column="1" x:Name="diagram" Width="500" Height="500" AllowDrop="true" />
    </Grid>
</Window>
 

Note the use of ShapeNode and ShapeNodeTest in the NodeListView. If I drag the ShapeNode in, it works fine. If I drag in ShapeNodeTest, I get the exception. Also note that this code works and creates the node successfully in the diagram:

void MainWindow_Loaded(object sender, RoutedEventArgs e) {
    var test2 = new ShapeNodeTest { Bounds = new Rect(100, 100, 30, 30), Shape = Shapes.Rectangle };
    diagram.Nodes.Add(test2);
}
 

Is there something I need to know about inheriting from ShapeNode?

Thanks,

David Cater

Hi,

I also made a class which inherits from ShapeNode. And I'm getting the same nullreferenceexception when trying to drag and drop it from a nodelistview onto a diagram. In the case of overriding the Clone method, what exactly do I need to add?

Thanks in advance!
Vincent

Hi,

I've implemented the example into my class but I'm still getting the null reference exception.

My code looks like this:

class BR_Shape : ShapeNode
    {
        protected Shape_Type type;
        public string header { get; protected set; }
        public int Priority { get; set; }

        public BR_Shape()
        {
            Priority = 0;
        }

        public BR_Shape(BR_Shape prototype) : base(prototype)
        {
            Priority = prototype.Priority;
        }

        public override DiagramItem Clone(bool clipboard)
        {
            return base.Clone(clipboard);
        }

        protected override void SaveToXml(XmlElement xmlElement, XmlPersistContext context)
        {
            base.SaveToXml(xmlElement, context);
            context.WriteInt(Priority, "Priority", xmlElement);
        }

        protected override void LoadFromXml(XmlElement xmlElement, XmlPersistContext context)
        {
            base.LoadFromXml(xmlElement, context);
            Priority = context.ReadInt("Priority", xmlElement);
        }
    }
 

I also have another class which inherits from NodeListView. In this class I add the shape to the items collection. Do I have to override some methods there as well?

Thanks in advance!
Vincent

Hi,

This is the stacktrace of the exception:

System.NullReferenceException was unhandled
  HResult=-2147467261
  Message=Object reference not set to an instance of an object.
  Source=WindowsBase
  StackTrace:
       at MindFusion.Diagramming.Wpf.Diagram.OnDrop(DragEventArgs e)
       at System.Windows.UIElement.OnDropThunk(Object sender, DragEventArgs e)
       at System.Windows.DragEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
       at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
       at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
       at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
       at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
       at System.Windows.UIElement.RaiseEvent(RoutedEventArgs e)
       at System.Windows.OleDropTarget.RaiseDragEvent(RoutedEvent dragEvent, Int32 dragDropKeyStates, Int32& effects, DependencyObject target, Point targetPoint)
       at System.Windows.OleDropTarget.MS.Win32.UnsafeNativeMethods.IOleDropTarget.OleDrop(Object data, Int32 dragDropKeyStates, Int64 point, Int32& effects)
       at MS.Win32.UnsafeNativeMethods.DoDragDrop(IDataObject dataObject, IOleDropSource dropSource, Int32 allowedEffects, Int32[] finalEffect)
       at System.Windows.OleServicesContext.OleDoDragDrop(IDataObject dataObject, IOleDropSource dropSource, Int32 allowedEffects, Int32[] finalEffect)
       at System.Windows.DragDrop.OleDoDragDrop(DependencyObject dragSource, DataObject dataObject, DragDropEffects allowedEffects)
       at System.Windows.DragDrop.DoDragDrop(DependencyObject dragSource, Object data, DragDropEffects allowedEffects)
       at MindFusion.Diagramming.Wpf.NodeListView.OnPreviewMouseMove(MouseEventArgs e)
       at System.Windows.UIElement.OnPreviewMouseMoveThunk(Object sender, MouseEventArgs e)
       at System.Windows.Input.MouseEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
       at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
       at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
       at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
       at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
       at System.Windows.UIElement.RaiseTrustedEvent(RoutedEventArgs args)
       at System.Windows.UIElement.RaiseEvent(RoutedEventArgs args, Boolean trusted)
       at System.Windows.Input.InputManager.ProcessStagingArea()
       at System.Windows.Input.InputManager.ProcessInput(InputEventArgs input)
       at System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport)
       at System.Windows.Interop.HwndMouseInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawMouseActions actions, Int32 x, Int32 y, Int32 wheel)
       at System.Windows.Interop.HwndMouseInputProvider.FilterMessage(IntPtr hwnd, WindowMessage msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
       at System.Windows.Interop.HwndSource.InputFilterMessage(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.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
       at System.Windows.Threading.Dispatcher.Run()
       at System.Windows.Application.RunDispatcher(Object ignore)
       at System.Windows.Application.RunInternal(Window window)
       at System.Windows.Application.Run(Window window)
       at System.Windows.Application.Run()
       at MindFusionDemo2.App.Main() in c:\Users\vjong\Documents\Visual Studio 2012\Projects\DragDropExample\MindFusionDemo2\obj\Debug\App.g.cs:line 0
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       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()
  InnerException:

 

I've added a method that should show a message box with some text to the EventHandler but that method isn't called.

Thanks in advance!
Vincent

It works now! I had child classes of my own class that inherits from ShapeNode and I had to add the copy constructor there as well.

Thanks for all the help! 

Vincent