Android NDK 和 Gradle：每种构建类型都有不同的 Android.mk

Question

我的本​​机库包含我想在编译时删除的日志。 通过在LOCAL_CFLAGS 中定义预处理器宏ENABLE_DEBUG 来显示日志，如下所示：

include $(CLEAR_VARS)
LOCAL_MODULE    := native-stuff
LOCAL_SRC_FILES := Native.cpp
LOCAL_LDLIBS := -llog
LOCAL_CFLAGS := -DENABLE_DEBUG
include $(BUILD_SHARED_LIBRARY)

我正在通过 Android Studio 使用 Gradle 构建应用程序，我想要另一个没有 LOCAL_CFLAGS := -DENABLE_DEBUG 的 Android.mk 文件用于发布构建，从而有效地禁用日志记录。

我尝试通过在src 下创建文件夹release/jni 并放置一个没有CFLAGS 的Android.mk 副本来做到这一点。它成功构建和部署，但我仍然看到日志。这是我的build.gradle：

apply plugin: 'com.android.library'

android {
    compileSdkVersion 21
    buildToolsVersion "21.1.2"

    defaultConfig {
        minSdkVersion 17
        targetSdkVersion 21
        versionCode 1
        versionName "1.0"
    }

    sourceSets {
        main {
            //Tell Gradle where to put the compiled shared library
            jniLibs.srcDir 'src/main/libs'

            //disable automatic ndk-build call
            jni.srcDirs = [];
        }
        release {
            jni.srcDirs = [];
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }

    // Tell Gradle the run the ndkBuild task when compiling
    tasks.withType(JavaCompile) {
        compileTask -> compileTask.dependsOn ndkBuild
    }

    // This task utilizes the Android.mk file defined in src/main/jni so that you
    // have more control over the build parameters (like library inclusion)
    // The system must define property 'androidNdkHome' in ~/.gradle/gradle.properties file
    // to point to NDK path
    task ndkBuild(type: Exec) {
        commandLine "$androidNdkHome/ndk-build", '-C', file('src/main/jni').absolutePath
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:support-v4:21.0.2'
}

我的项目结构如下：

src/
   main/
       jni/
          Android.mk
   release/
       jni/
          Android.mk

有没有可能做我想做的事？

Answer 1

我想我在这里找到了解决方案。它不像我希望的那样漂亮（尤其是因为它涉及创建一个临时文件），但我已经对其进行了测试并且它按预期工作。

我编写此代码是为了使用另一个 Application.mk 进行调试构建，称为 Application-debug.mk。你可以在里面放APP_CFLAGS := -DENABLE_DEBUG 做你想做的事。

关于它如何工作的评论在代码中。如果是应用程序构建文件，请使用applicationVariants.all 而不是libraryVariants.all：

android.libraryVariants.all { variant ->  // executes this block for each variant, current and futures
    def task = tasks.create(name: "ndk${variant.buildType.name.capitalize()}Build") { //create ndkReleaseBuild and ndkDebugBuild tasks
        doLast {
            exec { //execute all this block when the task is executed. (A Build task gets only the commandLine to be executed, so here we're using doLast.exec instead)
                def extraParameter = ""
                def rebuildFlag = ""

                if (variant.buildType.name == "debug")
                    extraParameter = "NDK_APPLICATION_MK=" + file('src/main/jni/Application-debug.mk').absolutePath //reference to another Application.mk to use when doing a debug build.

                def lastBuildFile = file('src/main/jni/.lastbuild.tmp') //save the last build type to a temp file, to avoid triggering rebuilds all the time.
                if (!lastBuildFile.exists())
                    lastBuildFile.createNewFile()

                def lastBuildType = lastBuildFile.text
                if (lastBuildType != variant.buildType.name) {
                    println "== ndk build variant has changed, triggering full rebuild. =="
                    rebuildFlag = "-B"
                }

                if (Os.isFamily(Os.FAMILY_WINDOWS)) {
                    commandLine 'ndk-build.cmd', rebuildFlag, '-C', file('src/main').absolutePath, extraParameter
                } else {
                    commandLine 'ndk-build', rebuildFlag, '-C', file('src/main').absolutePath, extraParameter
                }

                lastBuildFile.write(variant.buildType.name)
            }
        }
    }
    variant.javaCompile.dependsOn task
}

我也将此代码推送为要点：https://gist.github.com/ph0b/92f1f664c453869636f8