MAUI Blazor in .NET 9 does not run on Android API level 31 and below

[thomasbach-dk]

Description

I am currently playing with an upgrade from .NET 8 to .NET 9. We have a .NET MAUI Blazor (Hybrid) app, and when we run the app on Android (emulator) API level 31 we get the following console error:

11-14 13:12:32.688 I/chromium(12480): [INFO:CONSOLE(1)] "Uncaught SyntaxError: Unexpected token '{'", source: https://0.0.0.0/_framework/blazor.webview.js (1)
[INFO:CONSOLE(1)] "Uncaught SyntaxError: Unexpected token '{'", source: https://0.0.0.0/_framework/blazor.webview.js (1)

This error prevents the app from loading.

Running the app on Android API level 32 and above the issue does not occur.

In terms of the documentation of .NET 9 Android API level 24 should be supported.

UPDATE:
I figured out that updating the Android System WebView in the emulator fixed this issue.

Steps to Reproduce

No response

Link to public reproduction project repository

No response

Version with bug

9.0.0 GA

Is this a regression from previous behavior?

Yes, this used to work in .NET MAUI

Last version that worked well

8.0.402

Affected platforms

Android

Affected platform versions

Android API level 31 and below (Android 12 and below)

Did you find any workaround?

No

Relevant log output

11-14 13:12:32.688 I/chromium(12480): [INFO:CONSOLE(1)] "Uncaught SyntaxError: Unexpected token '{'", source: https://0.0.0.0/_framework/blazor.webview.js (1)
[INFO:CONSOLE(1)] "Uncaught SyntaxError: Unexpected token '{'", source: https://0.0.0.0/_framework/blazor.webview.js (1)

[caoyiliang]

我也发生了，我是Android10，使用新建的项目出现了同样的错误,设备链接：https://www.zebra.cn/cn/zh/support-downloads/mobile-computers/handheld/tc21.html

[Ying-6]

This issue has been verified using Visual Studio 17.13.0 Preview 1.0 (9.0.10 & 9.0.0). Can repro this issue. Works fine on 8.0.40 & 8.0.100.

[Eilon]

Possible dupe: dotnet/aspnetcore#53699 (the error in the other issue is slightly different, but possibly same root cause)

[danroth27]

Closing as a duplicate of dotnet/aspnetcore#53699

[capdiem]

So this is a BREAKING CHANGE and cannot be avoided 👎

[danroth27]

So this is a BREAKING CHANGE and cannot be avoided 👎

@capdiem Are you seeing your app end users impacted by this change? Or are you only hitting this during development with the Android emulator? Our theory here is that most app users will have an up-to-date web view on Android.

[capdiem]

@danroth27 We have various testing phones with different versions and models to ensure that users do not encounter issues on their devices. A phone running Android 11 with WebView version 90.0.4430.210 is not functioning properly after the upgrade.

This link points to a Chrome version 90.0.4427.0, which also encounters this error. The error points to the static keyword.

[capdiem]

@danroth27 I found that the issue is not with TypeScript, but rather that the generated release file contains the code static{this.nextEventDelegatorId=0}. Normally, it should generate static nextEventDelegatorId = 0. You can find in https://github.com/dotnet/aspnetcore/blob/main/src/Components/Web.JS/dist/Release/blazor.webassembly.js

[danroth27]

A phone running Android 11 with WebView version 90.0.4430.210 is not functioning properly after the upgrade.

@capdiem That WebView version is very old. Is this a physical device that just hasn't had it's WebView updated? Or is this an emulated device with the default WebView version that came with Android 11?

To be clear, our official support policy is that we only support the latest browser versions. Since most users have browsers that automatically update, we find this generally isn't an issue for deployed apps. I'd like to understand if your end users are actually impacted by this limitation or if this is just a test infrastructure issue.