编译

在您的Android crate的项目根目录下运行 cargo apk build。您可以与常规的 cargo build 使用相同的选项。

这将构建一个Android包，位于 target/android-artifacts/<debug|release>/apk。

编译多个二进制文件

cargo apk build 支持使用与 cargo build 相同的参数构建多个二进制文件和示例。它将为每个二进制文件生成一个APK。

为bin目标构建的Android包位于 target/android-artifacts/<debug|release>/apk。

为example目标构建的Android包位于 target/android-artifacts/<debug|release>/apk/examples。

在Android模拟器上测试

启动模拟器，然后运行

cargo apk run

这将安装您的应用程序到模拟器，然后运行它。
如果只想安装，请使用 cargo apk install。

要显示日志，请运行： cargo apk logcat | grep RustAndroidGlueStdouterr

与Android交互

如果一个应用程序无法访问屏幕、用户输入等，那么它将非常无趣。

android_glue crate提供了与Android环境的外部函数接口（FFI），用于处理不在stdlib中的事物。

它的工作原理

构建过程

构建过程通过以下方式工作：

• 使用rustc始终将您的crate编译为共享库
  • 创建自定义CMake工具链文件并设置环境变量，这些变量公开了NDK提供的适当构建工具，以便与cc和cmake crate一起使用。
  • 在crate根目录相同的目录下创建一个临时文件。这个临时文件作为静态库的crate根。它包含原始crate根的内容以及android_main的实现。
  • 编译android_native_app_glue的分支版本。android_native_app_glue最初由NDK提供。它提供了Android的NativeActivity使用的入口点，该入口点调用android_main。
  • 使用NDK提供的链接器进行链接。

这一步输出一个共享库，并且针对每个目标架构运行一次。

然后使用共享库、生成的清单文件和Android SDK中的工具构建APK。如果使用C++标准库，则将其添加到APK中。它使用Android开发工具默认的调试密钥库签名APK。如果密钥库不存在，则使用JRE或JDK中的keytool创建它。

支持的[package.metadata.android]条目

# The target Android API level.
# "android_version" is the compile SDK version. It defaults to 29.
# (target_sdk_version defaults to the value of "android_version")
# (min_sdk_version defaults to 18) It defaults to 18 because this is the minimum supported by rustc.
android_version = 29
target_sdk_version = 29
min_sdk_version = 26

# Specifies the array of targets to build for.
# Defaults to "armv7-linux-androideabi", "aarch64-linux-android", "i686-linux-android".
build_targets = [ "armv7-linux-androideabi", "aarch64-linux-android", "i686-linux-android", "x86_64-linux-android" ]

# The following values can be customized on a per bin/example basis. See multiple_targets example
# If a value is not specified for a secondary target, it will inherit the value defined in the `package.metadata.android`
# section unless otherwise noted.
#

# The Java package name for your application.
# Hyphens are converted to underscores.
# Defaults to rust.<target_name> for binaries. 
# Defaults to rust.<package_name>.example.<target_name> for examples.
# For example: for a binary "my_app", the default package name will be "rust.my_app"
# Secondary targets will not inherit the value defined in the root android configuration.
package_name = "rust.cargo.apk.advanced"

# The user-friendly name for your app, as displayed in the applications menu.
# Defaults to the target name
# Secondary targets will not inherit the value defined in the root android configuration.
label = "My Android App"

# Internal version number used to determine whether one version is more recent than another. Must be an integer.
# Defaults to 1
# See https://developer.android.com.cn/guide/topics/manifest/manifest-element
version_code = 2

# The version number shown to users.
# Defaults to the cargo package version number
# See https://developer.android.com.cn/guide/topics/manifest/manifest-element
version_name = "2.0"

# Path to your application's resources folder.
# If not specified, resources will not be included in the APK
res = "path/to/res_folder"

# Virtual path your application's icon for any mipmap level.
# If not specified, an icon will not be included in the APK.
icon = "@mipmap/ic_launcher"

# Path to the folder containing your application's assets.
# If not specified, assets will not be included in the APK
assets = "path/to/assets_folder"

# If set to true, makes the app run in full-screen, by adding the following line
# as an XML attribute to the manifest's <application> tag :
#     android:theme="@android:style/Theme.DeviceDefault.NoActionBar.Fullscreen
# Defaults to false.
fullscreen = false

# The maximum supported OpenGL ES version , as claimed by the manifest.
# Defaults to 2.0.
# See https://developer.android.com.cn/guide/topics/graphics/opengl.html#manifest
opengles_version_major = 3
opengles_version_minor = 2

# Adds extra arbitrary XML attributes to the <application> tag in the manifest.
# See https://developer.android.com.cn/guide/topics/manifest/application-element.html
[package.metadata.android.application_attributes]
"android:debuggable" = "true"
"android:hardwareAccelerated" = "true"

# Adds extra arbitrary XML attributes to the <activity> tag in the manifest.
# See https://developer.android.com.cn/guide/topics/manifest/activity-element.html
[package.metadata.android.activity_attributes]
"android:screenOrientation" = "unspecified"
"android:uiOptions" = "none"

# Adds a uses-feature element to the manifest
# Supported keys: name, required, version
# The glEsVersion attribute is not supported using this section. 
# It can be specified using the opengles_version_major and opengles_version_minor values
# See https://developer.android.com.cn/guide/topics/manifest/uses-feature-element
[[package.metadata.android.feature]]
name = "android.hardware.camera"

[[package.metadata.android.feature]]
name = "android.hardware.vulkan.level"
version = "1"
required = false

# Adds a uses-permission element to the manifest.
# Note that android_version 23 and higher, Android requires the application to request permissions at runtime.
# There is currently no way to do this using a pure NDK based application.
# See https://developer.android.com.cn/guide/topics/manifest/uses-permission-element
[[package.metadata.android.permission]]
name = "android.permission.WRITE_EXTERNAL_STORAGE"
max_sdk_version = 18

[[package.metadata.android.permission]]
name = "android.permission.CAMERA"

环境变量

Cargo-apk设置环境变量，这些变量用于将适当的C和C++构建工具暴露给构建脚本。主要目的是支持构建具有使用cc和cmake crate的构建脚本的crate。

• CC：NDK提供的针对适当目标和android平台的clang包装器的路径。
• CXX：NDK提供的针对适当目标和android平台的clang++包装器的路径。
• AR：NDK提供的ar的路径。
• CXXSTDLIB：使用NDK提供的完整功能的C++标准库。
• CMAKE_TOOLCHAIN_FILE：生成CMake工具链的路径。此工具链设置ABI，覆盖任何指定的目标，并包含NDK提供的目标链。
• CMAKE_GENERATOR：Unix Makefiles默认为Unix Makefiles，而不是使用CMake的默认设置，这取决于平台可能不合适。
• CMAKE_MAKE_PROGRAM：NDK提供的make的路径。

C++标准库兼容性问题

当crate链接到C++标准库时，使用NDK提供的共享库版本。不幸的是，依赖项加载问题会导致应用程序在较旧的Android版本上崩溃。一旦所有平台上的lld链接器问题得到解决，cargo apk将更新为链接到静态C++库。这应该解决兼容性问题。