Allow the use of .NET Core 10

.github/workflows/ci.yml

@@ -251,7 +251,8 @@ jobs:
         backend:
         - "macOS-x86_64"
         - "macOS-arm64"
-        - "windows"
+        - "windows-x86_64"
+        - "windows-arm64"
         - "linux-x11-gtk3"
         - "linux-wayland-gtk3"
         - "linux-wayland-gtk4"
@@ -489,11 +490,16 @@ jobs:
           briefcase-run-args: --config 'requires=["toga-core", "toga-textual"]' --config 'console_app=true'
           app-user-data-path: '$HOME\AppData\Local\Tiberius Yak\Toga Testbed\Data'
 
-        - backend: "windows"
+        - backend: "windows-x86_64"
           platform: "windows"
           runs-on: "windows-latest"
           app-user-data-path: '$HOME\AppData\Local\Tiberius Yak\Toga Testbed\Data'
 
+        - backend: "windows-arm64"
+          platform: "windows"
+          runs-on: "windows-11-arm"
+          app-user-data-path: '$HOME\AppData\Local\Tiberius Yak\Toga Testbed\Data'
+
         - backend: "iOS"
           platform: "iOS"
           runs-on: "macos-latest"

changes/2782.feature.md

@@ -0,0 +1 @@
+Toga's WinForms backend can now be used on ARM64 machines with a native ARM64 Python interpreter.

docs/en/reference/platforms/windows.md

@@ -8,11 +8,13 @@ The Toga backend for Windows is [`toga-winforms`](https://github.com/beeware/tog
 
 `toga-winforms` requires Python 3.10+, and Windows 10 or newer.
 
-/// note | Note
+Toga requires the use of either .NET Framework 4.x, or .NET Core 10.
 
-Toga uses the [Python.NET](https://pythonnet.github.io) library to access the underlying Winforms GUI toolkit on Windows. Unfortunately, Python.NET doesn't always keep up with the release schedule of Python itself, and as a result, may not be compatible with recently-released versions of Python (i.e., a Python release with a version number of 3.X.0 or 3.X.1). If you experience problems installing Toga, and you're using a recently-released version of Python, try downgrading to the previous minor release (e.g. 3.13.9 instead of 3.14.0).
+If you're on an x86-64 machine, .NET Framework 4.x is installed by default on Windows 10 and 11. Toga will use .NET Core 10 if it is installed.
+
+If you're using an ARM64 machine, and you're using a native ARM64 Python interpreter, you *must* use .NET Core 10. The [.NET Desktop Runtime can be downloaded from the .NET website](https://dotnet.microsoft.com/en-us/download/dotnet/10.0). If you're using an x86-64 interpreter on an ARM64 machine, Toga can use the .NET Framework install that is provided by default.
 
-///
+Toga uses the [Python.NET](https://pythonnet.github.io) library to access the underlying Winforms GUI toolkit on Windows. Unfortunately, Python.NET doesn't always keep up with the release schedule of Python itself, and as a result, may not be compatible with recently-released versions of Python (i.e., a Python release with a version number of 3.X.0 or 3.X.1). If you experience problems installing Toga, and you're using a recently-released version of Python, try downgrading to the previous minor release (e.g. 3.13.9 instead of 3.14.0).
 
 If you are using Windows 10 and want to use a WebView to display web content, you will also need to install the [Edge WebView2 Evergreen Runtime.](https://developer.microsoft.com/en-us/microsoft-edge/webview2/#download) Windows 11 has this runtime installed by default.
 

winforms/src/toga_winforms/__init__.py

@@ -1,3 +1,58 @@
+import platform
+from pathlib import Path
+
+import clr_loader
+from pythonnet import set_runtime
+
+try:
+    ####################################################################################
+    # Toga Winforms requires the use of .NET; either .NET Framework 4.x, or .NET Core.
+    #
+    # .NET Framework 4.x is available by default on Windows 10 and 11. However, on
+    # Windows on ARM64, it is an x86-64 binary, so it can't be used by a native ARM64
+    # Python interpreter.
+    #
+    # However, it *can* be used if you have an x86-64 Python interpreter - which is what
+    # you get if you run `py install -3.13` or `py install -3.14`. This will apparently
+    # change with Python 3.15.
+    #
+    # Using .NET Core requires a separate install - but it will be present on a lot
+    # of systems.
+    #
+    # So - try to load .NET Core; if it succeeds, use it. If the load fails, fall back
+    # to .NET Framework. If we're on ARM64, check to see if the interpreter is running
+    # in emulation mode. If it is, we're OK; if we're not, stop the interpreter; the
+    # .NET gives instructions on how to install .NET
+    ####################################################################################
+
+    # runtime.json defines the .NET version. .NET 10 is the current LTS release.
+    set_runtime(
+        clr_loader.get_coreclr(
+            runtime_config=Path(__file__).parent / "resources/runtime.json"
+        )
+    )
+
+    # .NET Core load succeeded
+    _use_dotnet_core = True
+except (clr_loader.util.clr_error.ClrError, RuntimeError):
+    # .NET Core load failed.
+    if platform.machine() == "ARM64" and "ARM64" in platform.python_compiler():
+        # A native ARM64 machine running an ARM64 Python.
+        # .NET Framework 4.x isn't an option.
+        raise RuntimeError("""
+
+On Windows, Toga requires .NET Core 10. Please visit:
+
+    https://dotnet.microsoft.com/en-us/download/dotnet/10.0
+
+and install the .NET Desktop Runtime.""") from None
+    else:
+        # Either a native x86_64 machine, or an ARM64 machine with
+        # and x86_64 Python interpreter in emulation mode. We can
+        # use .NET Framework 4.x
+        _use_dotnet_core = False
+
+
 import clr
 import travertino
 
@@ -9,6 +64,12 @@
 # Add a reference to the Winforms assembly
 clr.AddReference("System.Windows.Forms")
 
+# .NET Core requires some other explicit assemblies
+if _use_dotnet_core:
+    clr.AddReference("Microsoft.Win32.SystemEvents")
+    clr.AddReference("System.Windows.Extensions")
+
+
 # Add a reference to the WindowsBase assembly. This is needed to access
 # System.Windows.Threading.Dispatcher.
 #

winforms/src/toga_winforms/resources/runtime.json

@@ -0,0 +1,15 @@
+{
+  "runtimeOptions": {
+    "tfm": "net10.0-windows",
+    "frameworks": [
+      {
+        "name": "Microsoft.NETCore.App",
+        "version": "10.0.0"
+      },
+      {
+        "name": "Microsoft.WindowsDesktop.App",
+        "version": "10.0.0"
+      }
+    ]
+  }
+}