Pythonnet Error: XamlParseException : 'Failed to create a 'Click' from the text

Question

I was working on IronPython before (with WPF for developing some GUIs), and recently I started to try pythonnet.

But I found that the xaml file that worked on IronPython does not work on CPython + pythonnet. In IronPython, I can define a Button.Click in the xaml file, but it seems not possible in CPython. I have tried to look up for the answers, but nothing relevant was found. So hopefully you could save me here...

Here is my main script:

import clr
clr.AddReference(r"wpf\PresentationFramework")
from System.IO import StreamReader
from System.Windows.Markup import XamlReader
from System.Windows import Application, Window
from System.Threading import Thread, ThreadStart, ApartmentState

class MyWindow(Window):
    def __init__(self):
        stream = StreamReader('test.xaml')
        window = XamlReader.Load(stream.BaseStream)
        Application().Run(window)

    def Button_Click(self, sender, e):
        print('Button has clicked')

if __name__ == '__main__':
    thread = Thread(ThreadStart(MyWindow))
    thread.SetApartmentState(ApartmentState.STA)
    thread.Start()
    thread.Join()

And here is the test.xmal:

<Window 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    Title="WpfApplication1" Height="300" Width="300"> 
    <Grid>
        <Button x:Name="BUTTON" Content="Button" HorizontalAlignment="Left" Margin="101,82,0,0" VerticalAlignment="Top" Width="75" Click="Button_Click" Background="#FFFF1616"/>
    </Grid>
</Window>

The error message I got is:

Unhandled Exception: Python.Runtime.PythonException: XamlParseException : 'Failed to create a 'Click' from the text 'Button_Click'.' Line number '6' and line position '132'.

Strangly if I load the same xaml and keep the same Class structure in IronPython, the script works just fine:

import wpf
from System.Windows import Application, Window

class MyWindow(Window):
    def __init__(self):
        self.ui = wpf.LoadComponent(self, 'test.xaml')

    def Button_Click(self, sender, e):
        print('Button has clicked')

if __name__ == '__main__':
    Application().Run(MyWindow())

Thank you very much for help!

It seems IronPython was somehow able to read your event handler definition while python.net did not. Can you try if defining Button_Click before __init__ works? If it does not that most probably you 'll have to attach event handler in code and not in xaml. — Dipen Shah
– Dipen Shah, Commented Sep 24, 2018 at 14:46
Thanks for the comment Dipen, It does not work though. I got the same error message. — Y.Wang
– Y.Wang, Commented Sep 24, 2018 at 15:02

sanzoghenzo · Accepted Answer · 2024-12-30 06:53:44Z

2

you cannot import wpf in python using python.net package. But you can load the XAML file using PresentationFramework, even though presentationframework under python.net has some limitation. The XamlReader can't perform event handling, so we can manually add the event for that button in the python file, not in the XAML file.

here the gui.xaml code

<Window 
       xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
       xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
       Title="WpfApplication1" Height="300" Width="300">
    <Grid>
        <Label Content="Hello world" HorizontalAlignment="Left" Height="32" Margin="65,77,0,0" VerticalAlignment="Top" Width="119"/>
        <Button Name="button1" Content="Button" HorizontalAlignment="Left" Margin="65,145,0,0" VerticalAlignment="Top" Width="75"/>
    </Grid>
</Window>

Then here the python code

import clr
clr.AddReference("wpf\PresentationFramework") 
from System.IO import *
from System.Windows.Markup import XamlReader
from System.Windows import *
from System.Threading import Thread, ThreadStart, ApartmentState
from System.Windows.Controls import *

class MyWindow(Window):
    def __init__(self):
        try:
            stream = StreamReader('gui.xaml')
            self.window = XamlReader.Load(stream.BaseStream)
            ButtoninXAML = LogicalTreeHelper.FindLogicalNode(self.window, "button1") 
            ButtoninXAML.Click +=  RoutedEventHandler(self.Button_Click)
            Application().Run(self.window)      
        except Exception as ex:
            print(ex)
    def Button_Click(self, sender, e):
        print('clicked')
        
        
if __name__ == '__main__':
    thread = Thread(ThreadStart(MyWindow))
    thread.SetApartmentState(ApartmentState.STA)
    thread.Start()
    thread.Join()

edited Dec 30, 2024 at 6:53

sanzoghenzo

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answered Aug 31, 2019 at 17:36

black perl

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2 Comments

Y.Wang Over a year ago

Thank you for your answer black perl. I tried something similar to your answer and it worked.

Christna Over a year ago

Thank you. I also needed to import LogicalTreeHelper and RoutedEventHandler from System.Windows import Application, Window, LogicalTreeHelper, RoutedEventHandler

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