New update:

I found why the stackoverflow happened, and how to avoid it and make MVVM model work. however, it did not entirely solve the problem.

The StackOverFlow was not directly because of the INotifyPropertyChanged interface, but because I used a class derived from it.

if I define my ViewModel as

class ViewModel(System.ComponentModel.INotifyPropertyChanged):

and implement all components such as clr.clrproperty, PropertyChanged, add_PropertyChanged, remove_PropertyChanged etc as previous posted, and assign this class to window.DataContext, everything actually worked.

The problem is that I used a derived class

class ViewModelBase(System.ComponentModel.INotifyPropertyChanged): where PropertyChanged, add_PropertyChanged, remove_PropertyChanged are implemented

then

class ViewModel(ViewModelBase): where clr.clrproperty is implemented.

This results in the StackOverflow....

To make a simpler case, I tested out the following code that is entirely self-contained.

import clr, System

class DotNetINotifyPropertyChanged(System.ComponentModel.INotifyPropertyChanged):

__namespace__ = "DotNetINotifyPropertyChanged"

def __init__(self):

super(DotNetINotifyPropertyChanged, self).__init__()

def add_PropertyChanged(self, value):

pass

def remove_PropertyChanged(self, value):

pass

c1=DotNetINotifyPropertyChanged()

c1.add_PropertyChanged("text")

print "C1 success"

class A(DotNetINotifyPropertyChanged):

__namespace__ = "A"

def __init__(self):

super(A,self).__init__()

a1 = A()

a1.add_PropertyChanged("text")

print "a1 success"

if you run it, you can see that "C1 success" is printed, but python can not find a1.add_PropertyChanged method and throws exception. which I believe is the direct cause of StackOverflow above.

Obviously, if DotNetINotifyPropertyChanged is derived from "object", the above code runs fine.

Therefore the question is, what is it that inheriting from .NET interface that is unique, that the method defined in base class is not inherited by child class?

Hansong

From: tony@pyxll.com
Date: Sun, 3 Apr 2016 15:40:17 +0000
Subject: Re: [Python.NET] How to handle INotifyPropertyChanged interface
To: hhspiny@pine.cc; pythondotnet@python.org

Yeah, it looks like the crash is probably because of the missing event implementation as suspected. I'm a bit surprised that it didn't fail earlier when trying to instantiate the type.

If you do get a chance to take a look at adding that functionality be sure to submit a pull request!

Best regards,

Tony

On Sun, Apr 3, 2016 at 4:30 PM Hansong Huang <hhspiny@live.com> wrote:

Tony,

thanks for the hint.

the event PropertyChanged was declared in INotifyPropertyChanged interface by pythonnet, but obviously not implemented.
[('PropertyChanged', <unbound event 'PropertyChanged'>),

anyway, the stackoverflow only happens if both following are present
1. the class is derived from INotifyPropertyChanged interface
2. the class exposes property back to .Net vis @clrproperty

which seems to prove that it is the PropertyChanged event that is not implemented in python class resulted in the crash.

I was not sure if .Net event can be handled by pythonnet. I found a few examples with IronPython, but there, a python class of "event" seems to be implemented instead.

Below is the stack trace

[External Code]
clr.dll!CallDescrWorkerInternal () Unknown
clr.dll!CallDescrWorkerWithHandler(struct CallDescrData *,int) Unknown
clr.dll!CallDescrWorkerReflectionWrapper(struct CallDescrData *,class Frame *) Unknown
clr.dll!RuntimeMethodHandle::InvokeMethod(class Object *,class PtrArray *,class SignatureNative *,bool) Unknown
mscorlib.ni.dll!00007fffb86e1ca4() Unknown
mscorlib.ni.dll!00007fffb8618272() Unknown
mscorlib.ni.dll!00007fffb867fc4a() Unknown
[External Code]
mscorlib.ni.dll!00007fffb86dbaf5() Unknown
mscorlib.ni.dll!00007fffb86d281f() Unknown
System.ni.dll!00007fffb77556d4() Unknown
System.ni.dll!00007fffb7755637() Unknown
System.ni.dll!00007fffb775541d() Unknown
PresentationFramework.ni.dll!00007fff96c1ca70() Unknown
PresentationFramework.ni.dll!00007fff96c23902() Unknown
PresentationFramework.ni.dll!00007fff96c22ea1() Unknown
PresentationFramework.ni.dll!00007fff96c22693() Unknown
PresentationFramework.ni.dll!00007fff96c223c9() Unknown
PresentationFramework.ni.dll!00007fff96c21a03() Unknown
PresentationFramework.ni.dll!00007fff96c0d84c() Unknown
PresentationFramework.ni.dll!00007fff96b97299() Unknown
PresentationFramework.ni.dll!00007fff96b9720e() Unknown
PresentationFramework.ni.dll!00007fff96c852f0() Unknown
WindowsBase.ni.dll!00007fff9f6f9bc9() Unknown
WindowsBase.ni.dll!00007fff9f6f9ac6() Unknown
WindowsBase.ni.dll!00007fff9f6fca2b() Unknown
mscorlib.ni.dll!00007fffb86ca79e() Unknown
mscorlib.ni.dll!00007fffb86ca637() Unknown
mscorlib.ni.dll!00007fffb86ca5f2() Unknown
WindowsBase.ni.dll!00007fff9f913810() Unknown
WindowsBase.ni.dll!00007fff9f6fc784() Unknown
WindowsBase.ni.dll!00007fff9f6f7c24() Unknown
WindowsBase.ni.dll!00007fff9f6f8061() Unknown
WindowsBase.ni.dll!00007fff9f6f9e53() Unknown
WindowsBase.ni.dll!00007fff9f6f9d82() Unknown
WindowsBase.ni.dll!00007fff9f6f9bc9() Unknown
WindowsBase.ni.dll!00007fff9f6f9ac6() Unknown
WindowsBase.ni.dll!00007fff9f6f7583() Unknown
WindowsBase.ni.dll!00007fff9f6f94ff() Unknown
WindowsBase.ni.dll!00007fff9f8c496a() Unknown
clr.dll!UMThunkStub () Unknown
user32.dll!UserCallWinProcCheckWow() Unknown
user32.dll!DispatchMessageWorker() Unknown
WindowsBase.ni.dll!00007fff9f730ee8() Unknown
WindowsBase.ni.dll!00007fff9f70d8fc() Unknown
PresentationFramework.ni.dll!00007fff96af98b3() Unknown
PresentationFramework.ni.dll!00007fff96af969d() Unknown
clr.dll!CallDescrWorkerInternal () Unknown
clr.dll!CallDescrWorkerWithHandler(struct CallDescrData *,int) Unknown
clr.dll!CallDescrWorkerReflectionWrapper(struct CallDescrData *,class Frame *) Unknown
clr.dll!RuntimeMethodHandle::InvokeMethod(class Object *,class PtrArray *,class SignatureNative *,bool) Unknown
mscorlib.ni.dll!00007fffb86e1c20() Unknown
mscorlib.ni.dll!00007fffb8618272() Unknown
[External Code]
clr.dll!UMThunkStub () Unknown
[External Code]
> WPFPy.py!threadStart Line 256 Python
[External Code]

From: tony@pyxll.com
Date: Sun, 3 Apr 2016 15:20:47 +0000
Subject: Re: [Python.NET] How to handle INotifyPropertyChanged interface
To: hhspiny@pine.cc; pythondotnet@python.org

What's the full stack trace?

I suspect it's something to do with the event declared on the interface not being implemented. The managed type constructed doesn't define any events, so that would cause the construction of the type of fail - which is probably the error you're getting (although without the stack trace it's just an educated guess).

It shouldn't be too hard to add events to the derived type if someone wanted to have a go at implementing it. The code is in the CreateDerivedType method in src/runtime/classderived.cs. To be consistent with how methods and properties work, it would need a clrevent function adding to the clr module (src/runtime/resource/clr.py) - maybe it could work like this:

class MyClass(INotifyPropertyChanged):
OnPropertyChanged = clr.clrevent(event_attributes, event_type)

Then in classderived.cs the class any clrevents on the python class could be added to the managed type using TypeBuilder.DefineEvent.

So, anyway - short answer is that what you're trying to do won't work without changes to pythonnet; but the changes required shouldn't be too hard if you wanted to have a go.

Best regards,
Tony

On Sun, Apr 3, 2016 at 3:37 PM Hansong Huang <hhspiny@live.com> wrote:

It seems inheriting from INotifyPropertyChanged is the cause

self.window = System.Windows.Markup.XamlReader.Load(outStream)
self.window.DataContext = MyViewModel()
class MyViewModel(System.Object):
__namespace__ = "WPFPyDemo"
def __init__(self):
super(MyViewModel,self).__init__()
self._inputText = "Line - in"
@clr.clrproperty(str)
def inputText(self):
return self._inputText
@inputText.setter
def inputText(self,value):
self._inputText = value
self.OnPropertyChanged("inputText")

The above code works fine.

but if switch inheritance to
class MyViewModel(System.ComponentModel.INotifyPropertyChanged):
and nothing else changed, python gives

"The process terminates due to StackOverflowException"

Not sure why.

Thanks for the help

From: hhspiny@live.com
To: pythondotnet@python.org
Subject: How to handle INotifyPropertyChanged interface
Date: Thu, 31 Mar 2016 20:38:38 -0400

I am still trying to figure out how to implement WPF MVVM with Python.Net.
Previously, I have successfully used System.Dynamic.ExpandoObject as a ViewModel container

self.window = System.Windows.Markup.XamlReader.Load(outStream)
self.window.DataContext = DotNetExpandoObject()

where DotNetExpandoObject is a wrapper class for System.Dynamic.ExpandoObject
class DotNetExpandoObject(System.Dynamic.ExpandoObject):
... in which I redefined __getattr__ and __setattr__

it works flawlessly as System.Dynamic.ExpandoObject implements INotifyPropertyChange interface already

Now, I would like to get away from using System.Dynamic.ExpandoObject but to implement my own

I first tried to expose a python class back to .Net
class MyViewModel(System.Object):
__namespace__ = "WPFPyDemo"
def __init__(self):
super(MyViewModel,self).__init__()
self._inputText = "Line - in"
@clr.clrproperty(str)
def inputText(self):
return self._inputText
@inputText.setter
def inputText(self,value):
self._inputText = value
self.OnPropertyChanged("inputText")

self.window.DataContext = MyViewModel()

The one direction data binding works fine, and the "Line - in" text correctly shows up in the textblock control.
obviously this is not sufficient as there is no INotifyPropertyChange interface.

So, I inherit the interface , and tries to implement the typical C# code
" public event PropertyChangedEventHandler PropertyChanged"

-- not sure how to handle event in Python.Net, the follow code probably is completely wrong

class ViewModel(System.ComponentModel.INotifyPropertyChanged):
__namespace__ = "WPFPy"
def __init__(self):
super(ViewModel, self).__init__()
self.PropertyChanged = System.ComponentModel.PropertyChangedEventHandler
def OnPropertyChanged(self, propertyName):
if self.PropertyChanged != None:
PropertyChanged(self, System.ComponentModel.PropertyChangedEventArgs(propertyName))

class MyViewModel(ViewModel):
__namespace__ = "WPFPyDemo"
def __init__(self):
super(MyViewModel,self).__init__()
self._inputText = "Line - in"

@clr.clrproperty(str)
def inputText(self):
return self._inputText
@inputText.setter
def inputText(self,value):
self._inputText = value
self.OnPropertyChanged("inputText")

The process terminates due to StackOverflowException.
Looks like the error happens when WFP recoganized INotifyPropertyChange interface and tries to access MyViewModel class via it.

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