Here is how I understand IronPython's implementation .Net expects an event to be defined by the class that implements INotifyPropertyChanged interface. However, as python does not support event type, IronPython created two methods at its interface with .Net: add_PropertyChanged and remove_PropertyChanged. hence, whenever .Net would add or remove a handler from this event, these two methods are called instead. then a separate python class is created within IronPython to actual track and invoke callback functions. well, looks like Python.Net implemented exactly the same as IronPython. dir(System.ComponentModel.INotifyPropertyChanged) ==>['PropertyChanged', '__class__', '__cmp__', '__delattr__', '__doc__', '__format__', '__getattribute__', '__hash__', '__init__', '__iter__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'add_PropertyChanged', 'remove_PropertyChanged']so, in principle the same implementation as in IronPython should work. but instead, I got stackoverflow here is my implementation:make_event() and event() and even_handler() classes are copied from IronPython examples, used to track and invoke callback functions class ViewModel(System.ComponentModel.INotifyPropertyChanged): ''' this does not work. PropertyChanged event can not be implemented yet''' __namespace__ = "ViewModel" PropertyChanged == None def __init__(self): super(ViewModel, self).__init__() self.PropertyChanged, self._propertyChangedCaller = make_event() @clr.clrmethod(None, [System.ComponentModel.PropertyChangedEventHandler]) def add_PropertyChanged(self, value): self.PropertyChanged += value @clr.clrmethod(None, [System.ComponentModel.PropertyChangedEventHandler]) def remove_PropertyChanged(self, value): self.PropertyChanged -= value def OnPropertyChanged(self, propertyName): if self.PropertyChanged != None: self._propertyChangedCaller(self, System.ComponentModel.PropertyChangedEventArgs(propertyName)) One possible reason might be that the types specified in @clr.clrmethod is not correct, therefore, .Net could not find the right method to call. Hansong

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Message: 1 Date: Sun, 3 Apr 2016 11:08:50 -0500 From: Denis Akhiyarov To: "A list for users and developers of Python for .NET" Subject: Re: [Python.NET] How to handle INotifyPropertyChanged interface Message-ID: Content-Type: text/plain; charset="utf-8"

is it possible to workaround this non-implemented feature by using ___setattr__() hook? seems like people were able to do this in ironpython:

http://stackoverflow.com/questions/3856905/

On Sun, Apr 3, 2016 at 10:40 AM, Tony Roberts wrote:

...

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 wrote:

...

Tony,

thanks for the hint.

the event PropertyChanged was declared in INotifyPropertyChanged interface by pythonnet, but obviously not implemented. [('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 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. _________________________________________________ Python.NET mailing list - PythonDotNet@python.org https://mail.python.org/mailman/listinfo/pythondotnet

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