Comments (6)
jonpryor
commented on May 18, 2024
1
The problem is that the error message isn't entirely useful. Build from the command-line, and get:
error MSB4018: The "GenerateJavaStubs" task failed unexpectedly. […/Scratch.Gxa1151/Scratch.Gxa1151/Scratch.Gxa1151.csproj]
error MSB4018: System.InvalidOperationException: The type 'Scratch.Gxa1151.MainActivity' needs to have a public default constructor. […/Scratch.Gxa1151/Scratch.Gxa1151/Scratch.Gxa1151.csproj]
error MSB4018: at Xamarin.Android.Tasks.ManifestDocument.Merge (System.Collections.Generic.List`1[T] subclasses, System.Collections.Generic.List`1[T] selectedWhitelistAssemblies, System.String applicationClass, System.Boolean embed, System.String bundledWearApplicationName, System.Collections.Generic.IEnumerable`1[T] mergedManifestDocuments) [0x004aa] in <acf4a3302c8d4a7eaf06af6dce1aafb2>:0 [… /Scratch.Gxa1151/Scratch.Gxa1151/Scratch.Gxa1151.csproj]
error MSB4018: at Xamarin.Android.Tasks.GenerateJavaStubs.Run (Java.Interop.Tools.Cecil.DirectoryAssemblyResolver res) [0x00491] in <acf4a3302c8d4a7eaf06af6dce1aafb2>:0 [… /Scratch.Gxa1151/Scratch.Gxa1151/Scratch.Gxa1151.csproj]
error MSB4018: at Xamarin.Android.Tasks.GenerateJavaStubs.Execute () [0x00225] in <acf4a3302c8d4a7eaf06af6dce1aafb2>:0 [… /Scratch.Gxa1151/Scratch.Gxa1151/Scratch.Gxa1151.csproj]
error MSB4018: at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute () [0x00023] in <76dd0031e0df4aa99d9befb4c4585c69>:0 [… /Scratch.Gxa1151/Scratch.Gxa1151/Scratch.Gxa1151.csproj]
error MSB4018: at Microsoft.Build.BackEnd.TaskBuilder+<ExecuteInstantiatedTask>d__26.MoveNext () [0x0022d] in <76dd0031e0df4aa99d9befb4c4585c69>:0 [… /Scratch.Gxa1151/Scratch.Gxa1151/Scratch.Gxa1151.csproj]
The bug is that Activity subclasses with an [Activity] custom attribute -- i.e. any type within AndroidManifest.xml that will be instantiated by Android -- must have a default constructor.
So we're doing the quasi-right thing here: there is an error, and we're reporting it.
The problem is the way we're reporting it: it's useless:
| Line | Description | File | Project | Path |
|---|---|---|---|---|
| 1794 | The "GenerateJavaStubs" task failed unexpectedly. | Xamarin.Android.Common.targets | Scratch.Gxa1151 | ../../../../../../Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets |
What we should report is, in the case of my example (I took the default template, and added a public MainActivity(string) constructor), report:
| Line | Description | File | Project | Path |
|---|---|---|---|---|
| 8 | XAwhatever: The type MainActivity must contain a default constructor. |
MainActivity.cs | Scratch.Gxa1151 | MainActivity.cs |
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jonpryor
commented on May 18, 2024
1
@asterixorobelix: Any type mentioned in AndroidManifest.xml -- any type which is created by Android -- must have a default constructor.
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JonDouglas
commented on May 18, 2024
@anirugu Can you upload a full diagnostic build output?
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commented on May 18, 2024
Thanks for reply, I will update you tonight !
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jonpryor
commented on May 18, 2024
Sketching out the fix:
Where we report the error needs to crib the LookupSource(TypeDefinition) method to obtain the filename and line number of the offending type, so that we can emit a better formed error message.
ManifestDocument.cs should also use log.LogError() instead of throwing the exception.
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asterixorobelix
commented on May 18, 2024
I have been having this issue too. After adding a blank constructor to the Activity, the error went away..
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