PyWebView与pythonnet兼容问题求助：解决空引用后遇下标错误

测试代码 #

import webview
webview.create_window('Hello world', 'https://pywebview.flowrl.com/hello')
webview.start()

遇到的错误 #

第一个错误 #

执行上述代码时出现以下异常：

Unbehandelte Ausnahme: System.NullReferenceException: Der Objektverweis wurde nicht auf eine Objektinstanz festgelegt.
   bei System.Windows.Forms.Control.get_CacheTextInternal()
   bei System.Windows.Forms.Control.get_Text()
   bei System.Windows.Forms.Control.set_Text(String value)
--- Ende der Stapel�berwachung vom vorhergehenden Ort, an dem die Ausnahme ausgel�st wurde ---
   bei System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   bei Python.Runtime.PythonException.ThrowLastAsClrException()
   bei Python.Runtime.Dispatcher.TrueDispatch(Object[] args)
   bei Python.Runtime.Dispatcher.Dispatch(Object[] args)
   bei __System_Threading_ThreadStartDispatcher.Invoke()
   bei System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   bei System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   bei System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   bei System.Threading.ThreadHelper.ThreadStart()

第二个错误 #

安装pythonnet 3.0.0a2尝试解决后，出现新错误：

Traceback (most recent call last):
File "C:\Users\User\Documents\Visual Studio Code\Python Projects\webviewTest.py", line 3, in <module>
webview.start()
File "C:\Users\User\AppData\Local\Programs\Python\Python39\lib\site-packages\webview\__init__.py", line 122, in start
guilib = initialize(gui)
File "C:\Users\User\AppData\Local\Programs\Python\Python39\lib\site-packages\webview\guilib.py", line 101, in initialize
if not try_import(guis):
File "C:\Users\User\AppData\Local\Programs\Python\Python39\lib\site-packages\webview\guilib.py", line 62, in try_import
if import_func():
File "C:\Users\User\AppData\Local\Programs\Python\Python39\lib\site-packages\webview\guilib.py", line 52, in import_winforms
import webview.platforms.winforms as guilib
File "C:\Users\User\AppData\Local\Programs\Python\Python39\lib\site-packages\webview\platforms\winforms.py", line 31, in <module>
import clr
File "C:\Users\User\AppData\Local\Programs\Python\Python39\lib\site-packages\clr.py", line 6, in <module>
load()
File "C:\Users\User\AppData\Local\Programs\Python\Python39\lib\site-packages\pythonnet\__init__.py", line 42, in load
func = _LOADER_ASSEMBLY["Python.Runtime.Loader.Initialize"]
TypeError: 'Assembly' object is not subscriptable

解决步骤 #

1. 降级pythonnet到稳定版 #

pythonnet 3.0.0a2是预发布版本，API存在兼容性问题，换成稳定版即可解决第二个错误：

• 卸载现有版本：

pip uninstall -y pythonnet clr

• 安装兼容的稳定版本：

pip install pythonnet==2.5.2

2. 强制使用CEF渲染引擎 #

如果WinForms后端依旧报错，直接指定PyWebView使用CEF引擎，兼容性更强：
修改代码如下：

import webview
webview.create_window('Hello world', 'https://pywebview.flowrl.com/hello')
webview.start(gui='cef')

首次运行时PyWebView会自动下载CEF依赖，等待下载完成后即可正常启动窗口。

3. 匹配Python版本 #

确保Python版本在3.8-3.10之间，过新或过旧的Python版本可能和PyWebView、pythonnet存在兼容性冲突。

内容的提问来源于stack exchange，提问作者Max Payne