Example code for AndroidApp::activity_as_ptr does not compile

[rnikander]

I'm trying to figure out how to get the native activity in my app code. For example, when I want to get access to my app's internal files directory.

The activity_as_ptr method looks promising, but that code causes an error:

let activity = unsafe { JObject::from_raw(app.activity_as_ptr()) };

error[E0308]: mismatched types
  --> my-app/src/lib.rs:75:47
   |
75 |     let activity = unsafe { JObject::from_raw(app.activity_as_ptr()) };
   |                             ----------------- ^^^^^^^^^^^^^^^^^^^^^ expected `*mut _jobject`, found `*mut c_void`
   |                             |
   |                             arguments to this function are incorrect
   |
   = note: expected raw pointer `*mut _jobject`
              found raw pointer `*mut c_void`

[rnikander]

I want to get one of these: NativeActivity

[MarijnS95]

@rnikander be aware that the pointer returned by activity_as_ptr() represents a Java Activity subclass, whereas you link to the NDK NativeActivity struct in your followup comment; those are two fundamentally incompatible objects. The latter is a native abstraction that holds a pointer to the Activity subclass inside.

The NativeActivity object is inherently internal to and fully managed by android-activity, giving anything else "raw" access to it is very likely to break its functionality and guarantees.

All "getter" functionality on NativeActivity (and that shared with GameActivity) is already directly available on AndroidApp, can you please confirm it already contains what you need or otherwise clarify the functionality that is missing?

---

That pointer needs a .cast() in the documentation, unfortunately the doc-example is strangely marked as ignore. Even without that, our docs are never even build-tested, cargo doc --target aarch64-linux-android nor cargo t --doc --target aarch64-linux-android -F native-activity even try.

@rib I think the way I solved that in the ndk is by having a test feature to disable the compile_error!() which would catch such issues in android-activity as well, and build-test "the docs" for the host architecture:

https://github.com/rust-mobile/ndk/blob/ec624f20263fcd31eb08cf36e41b36be6cb0e15e/ndk-sys/src/lib.rs#L21-L22

If I do that on a local branch, there's a lot more android-activity documentation that fails 😅