Support for Android

[lammermann]

Hi,
I would like to use this for a cross platform GUI. Is it possible to use this crate for mobile platforms like android? Are there any special quirks necessary to make it compile and to deploy it?

Thanks in advance

[Stuv7CB]

Hello, I'm not developer of this library but I have build my app as apk for android.
First of all one should add .cargo/config with paths to ar and linker from android ndk e.g.

[target.armv7-linux-androideabi]
ar = "/home/leonid/Android/ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/arm-linux-androideabi-ar"
linker = "/home/leonid/Android/ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/armv7a-linux-androideabi22-clang"

and one should add in one's $PATH path to qmake for android and set enviroment variable for
CXX to appropriate android compiler from ndk, because otherwise cxx crate wouldn't be able to build qmetaobject targeting android.
Also set output as cdylib and add function with following signature

#[no_mangle]
pub extern fn main(argc: i32, argv: *mut *mut i8) -> i32

After compiling source code to .so library you can create library with this https://doc.qt.io/qt-5/deployment-android.html
I don't find better way to produce apk from .so file than using this https://github.com/LaurentGomila/qt-android-cmake

If there is any better way to produce apk file I would like to know it.

[ogoffart]

Hi,

I suppose it should indeed work on android.
I'd accept merge requests that would help (code or documentation changes).

[lammermann]

@Stuv7CB Thank you for your help. However when I try to follow the steps I get an error message

cargo:warning=/usr/include/qt/QtCore/qprocessordetection.h:150:6: error: "ARM architecture too old"
cargo:warning=#    error "ARM architecture too old"
cargo:warning=     ^

It seems like the compiler does not set the necessary defines for the arm architecture (although it is the one from the android ndk). Have you encountered any errors like this?

[Stuv7CB]

@lammermann No, I haven't. But I can suggest that you targeting very old android platform. According Qt 5.13 documentation minimal supported API level is 21 i.e. you should use as compiler armv7a-linux-androideabi21-clang or higher.

[extraymond]

Hello, I'm not developer of this library but I have build my app as apk for android.
First of all one should add .cargo/config with paths to ar and linker from android ndk e.g.

[target.armv7-linux-androideabi]
ar = "/home/leonid/Android/ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/arm-linux-androideabi-ar"
linker = "/home/leonid/Android/ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/armv7a-linux-androideabi22-clang"

and one should add in one's $PATH path to qmake for android and set enviroment variable for
CXX to appropriate android compiler from ndk, because otherwise cxx crate wouldn't be able to build qmetaobject targeting android.
Also set output as cdylib and add function with following signature

#[no_mangle]
pub extern fn main(argc: i32, argv: *mut *mut i8) -> i32

After compiling source code to .so library you can create library with this https://doc.qt.io/qt-5/deployment-android.html
I don't find better way to produce apk from .so file than using this https://github.com/LaurentGomila/qt-android-cmake

If there is any better way to produce apk file I would like to know it.

@Stuv7CB

Hi! Thanks for sharing, if that's possible I would like to know your setup.
I've got ar and linker working, but happened to meet the following error:

cargo:warning=/usr/include/x86_64-linux-gnu/qt5/QtGui/qopengl.h:139:13: fatal error: 'GL/gl.h' file not found

My QT is installed from apt 5.9, tried the QT website one (5.14) by adding it to $PATH but didn't work.
If I specifically add QT_VERSION/android/bin to $PATH, then it complains about not being able to find QtCore and bunch of stuffs.

I've tried building for both x86_64 linux and aarch64-unknown-linux(provided the correct linker) and it all worked without needing to touch qt path if qmake reports to be using the x86_64 one installed on my system, I'm not sure what to do next. Thanks again.

[extraymond]

Updates about adding path to 5.14 and failed:

In 5.14 the lib is suffixed as QT5{lib}_{android_target}
So for example building for aarch-linux-android would need the build.rs script to change from:

println!(
        "cargo:rustc-link-lib{}=Qt{}Widgets",
        macos_lib_search, macos_lib_framework
    );

into one with correct plaftform suffix:

println!(
        "cargo:rustc-link-lib{}=Qt{}Widgets_arm64-v8a",
        macos_lib_search, macos_lib_framework
    );

Now I've build the libsomething.so, still need to figure out how to build an apk...

[extraymond]

Update about the naming convention, seems that it's not needed for the current lts release of QT 5.12, it's stored in different sub directories under QT_VER/VER/android_($ARCH)/

[asdf8dfafjk]

@extraymond Did you figure out the .so to .apk part yet? I do see Stuv7CB's link but I have no clue about cmake and don't know where to start

[asdf8dfafjk]

I tried using androiddeployqt by creating a settings json file based on another I found on github:

{
   "description": "This file has been handwritten based on some tool created file found on github",
   "qt": "/ext4_data/qt/Qt5.15.2/5.15.2/android/",
   "sdk": "/ext4_data/android",
   "sdkBuildToolsRevision": "33.0.1",
   "ndk": "/ext4_data/android/ndk/22.1.7171670/",
   "toolchain-prefix": "llvm",
   "tool-prefix": "llvm",
   "ndk-host": "linux-x86_64",
   "architectures": {"arm64-v8a":"aarch64-linux-android"},
   "android-package-source-directory": "/home/zx/sources/android-30",
   "android-min-sdk-version": "23",
   "android-target-sdk-version": "30",
   "qml-importscanner-binary": "/ext4_data/qt/Qt5.15.2/5.15.2/android/bin/qmlimportscanner",
   "rcc-binary": "/ext4_data/qt/Qt5.15.2/5.15.2/android/bin/rcc",
   "qml-root-path": "/code/zx/workspace/projects/mono/RustAndroid/QmlAndroid",
   "stdcpp-path": "/ext4_data/android/ndk/22.1.7171670/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib",
   "qrcFiles": "WHATGOESHERE",
   "application-binary": "QmlAndroid"
}

androiddeployqt --output x.apk

but sadly it fails with an error:

Cannot find application binary in build dir /code/zx/workspace/projects/mono/RustAndroid/QmlAndroid/x.apk//libs/arm64-v8a/libQmlAndroid_arm64-v8a.so.

As long as the android sdk source is correct, and everything else is garbage, this is the error I get. I did fill everything else to correct value except the qrc thing but I still get it. Not sure how to proceed.

[kalaksi]

I've also been trying to get this to work on Android. The CMake building process of Qt for Android is full of potholes and trial & error, but I now have built the package successfully (tested with Qt 5.15 and Qt 6.4), but the app crashes instantly. In logs, there are a bunch of "No implementation found" errors like "No implementation found for void org.qtproject.qt.android.QtNative.handleOrientationChanged(int, int) (tried Java_org_qtproject_qt_android_QtNative_handleOrientationChanged and Java_org_qtproject_qt_android_QtNative_handleOrientationChanged__II) - is the library loaded, e.g. System.loadLibrary?"

There are probably some issues in andrdoiddeployqt since it seems to skip platform plugin if not manually added. I've been copying over the missed libs in a build step before androiddeployqt. The libs will then get copied to the apk. If I instead add "libplugins_platforms_qtforandroid_@ANDROID_ABI@.so" in android-extra-libs, the error changes to "dlsym failed: undefined symbol: main". I have no idea if that's any better.

Anyone familiar with this? I can share more details, but I've been trying different versions for building, so my setup is still changing.