[Python.NET] How to handle INotifyPropertyChanged interface

[Hansong Huang]

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 classclass ViewModelBase(System.ComponentModel.INotifyPropertyChanged):  where PropertyChanged, add_PropertyChanged, remove_PropertyChanged are implementedthenclass 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, Systemclass DotNetINotifyPropertyChanged(System.ComponentModel.INotifyPropertyChanged):    __namespace__ = "DotNetINotifyPropertyChanged"    def __init__(self):        super(DotNetINotifyPropertyChanged, self).__init__()        def add_PropertyChanged(self, value):        pass    def remove_PropertyChanged(self, value):        passc1=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 at pyxll.com
Date: Sun, 3 Apr 2016 15:40:17 +0000
Subject: Re: [Python.NET] How to handle INotifyPropertyChanged interface
To: hhspiny at pine.cc; pythondotnet at 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 at 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 present1. the class is derived from INotifyPropertyChanged interface2. 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 at pyxll.com
Date: Sun, 3 Apr 2016 15:20:47 +0000
Subject: Re: [Python.NET] How to handle INotifyPropertyChanged interface
To: hhspiny at pine.cc; pythondotnet at 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 at 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 at live.com
To: pythondotnet at 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 .Netclass 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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