pywebview: Can't open a new window from the JS API

Specification

Platform: winforms
Version: 2.0.3

Description

My code looks a bit like this:

import os
import threading

import webview


class FirstWindowApi:
    def on_button(self):
        webview.destroy_window()
        t = threading.Thread(target=create_second_window)
        t.start()


class SecondWindowApi:
    pass


def create_second_window():
    second_window = webview.create_window("Window 2", os.path.abspath("web\\window2.html"), js_api=SecondWindowApi)



first_window = webview.create_window("Window 1", os.path.abspath("web\\window1.html"), js_api=FirstWindowApi)

However, when I click the button, it crashes with this exception:

Exception in thread Thread-3:
Traceback (most recent call last):
  File "C:\Program Files\Python36\lib\threading.py", line 916, in _bootstrap_inner
    self.run()
  File "C:\Program Files\Python36\lib\threading.py", line 864, in run
    self._target(*self._args, **self._kwargs)
  File "ui_pywebview.py", line 23, in create_second_window
    second_window = webview.create_window("Window 2", os.path.abspath("web\\window2.html"), js_api=SecondWindowApi)
  File "C:\Program Files\Python36\lib\site-packages\webview\__init__.py", line 183, in create_window
    background_color, debug, js_api, text_select, _webview_ready)
  File "C:\Program Files\Python36\lib\site-packages\webview\winforms.py", line 252, in create_window
    BrowserView.instances['master'].Invoke(Func[Type](create))
KeyError: 'master'

About this issue

Original URL
State: closed
Created 6 years ago
Comments: 22 (10 by maintainers)

Most upvoted comments

@TheInitializer as your case could be solved by switching the order of destroy_window and create_window, I see no reason in keeping application loop alive. Besides how would you terminate the application loop if a keep-alive feature would be implemented?

The threading model should be probably be documented in README.

r0x0r on May 30, 2018

QT had the same problem as Windows with restarting application loop. All the platforms should be fixed by now.

r0x0r on May 31, 2018

This time it is the expected behaviour. This is the proper exception pywebview raises if you try to call any api function on a non-existent window, as mentioned in our README:

In all cases, uid is the uid of the target window returned by create_window(); if no window exists with the given uid, an exception is thrown.

Just wrap your code within a try-except block and handle it yourself. Better than forcing your users to do something. 🙂

@r0x0r It seems my patch fixes this issue. Can we merge it to master? Let us open a new issue for tracking the app-termination-behaviour.

shivaprsd on May 23, 2018

Yes this is correct. Single window would always block control and release once closed.

r0x0r on May 21, 2018

Another related problem is that opening a second window after the closing the first one fails on Windows. Ie

webview.create_window(...) # close this window manually
webview.create_window(...) # this will fail

On OSX it terminates the whole app after the window is closed. Windows and QT fail, as they try to create a child window after the app is terminated. The culprit is the create_window initialization code in init.py.

I believe that the program should not terminate after the last window is closed, but instead give control to the user code and wait until it is finished executing. Opinions?

r0x0r on May 21, 2018