【转】Create Hello-JNI with Android Studio

【转】Create Hello-JNI with Android Studio

From:https://codelabs.developers.google.com/codelabs/android-studio-jni/index.html?index=..%2F..%2Findex#4

访问需要翻墙。

没有翻译成中文是因为图片很详细，看不懂英文，根据图片一步一步也能完成。另外开发人员应该具备阅读英文技术博客的能力。

1. Overview

In this codelab, you'll learn how to use Android Studio to start Android NDK PRoject development.

2. Create java Sample App

3. Add JNI Build Capability to HelloAndroidJni Project

Android Studio supports native development via experimental plugin developed by Google, let's add it into our project.

classpath 'com.android.tools.build:gradle:2.1.0'
with your latest version[it does not have to be 0.7.2]:
classpath 'com.android.tools.build:gradle-experimental:0.7.2'Change to the latest gradle version (2.10 is required for plugin version 0.7.0).Select Android Studio "Project" pane, "Gradle Scripts" > "gradle-wrapper.properties (Gradle Version)" and change:distributionUrl=https/://services.gradle.org/distributions/gradle-2.4-all.zipto:distributionUrl=https/://services.gradle.org/distributions/gradle-2.10-all.zipConvert the auto-generated module build.gradle to Gradle's component model DSL.Select Android Studio "Project" pane > "Gradle Scripts" > "build.gradle (Module: app)" and replace:
apply plugin: 'com.android.application' android {   compileSdkVersion 23   buildToolsVersion "23.0.1"    defaultConfig {       applicationId "com.google.sample.helloandroidjni"       minSdkVersion 22       targetSdkVersion 23       versionCode 1       versionName "1.0"   }   buildTypes {       release {           minifyEnabled false           proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'       }   }}// others below this line: no change
with:
apply plugin: 'com.android.model.application'model {   android {       compileSdkVersion 23       buildToolsVersion "23.0.3"       defaultConfig {           applicationId "com.google.sample.helloandroidjni"           minSdkVersion.apiLevel 22           targetSdkVersion.apiLevel 23           versionCode 1           versionName "1.0"       }       buildTypes {           release {               minifyEnabled false               proguardFiles.add(file('proguard-android.txt'))           }       }   }}// others below this line: no changeSync , Build and Run . You should still see the same "Hello World" on your target device.
4. Add JNI Code Into Project
Check the NDK Path.Select the menu "File" > "Project Structure" > "SDK Location", "Android NDK Location" if it is not set yet, then click "...", and browse to your NDK location and click "OK" (you may also choose "download").Configure the module build.gradle to create "hello-android-jni" shared lib.Select Android Studio "Project" pane > "Gradle Scripts" > "build.gradle (Module:app)", add the following inside the "model" block, after "buildTypes" block.
	
buildTypes {...}// New codendk {    moduleName "hello-android-jni"}// New code finishedAdd JNI function and load jni shared lib into project.Select Android Studio "Project" pane > "app" > "java" > "com.google.sample.helloandroidjni" > "MainActivity", and add JNI function getMsgFromJni() and System.loadLibrary() to the end of class MainActivity.
     
...   // new code   static {       System.loadLibrary("hello-android-jni");   }   publicnativeString getMsgFromJni();   // new code done} // class MainActivitySync , Build , there should be no errors from Android Studio.
Note:
make sure library name is the same as moduleName inside build.gradleThe "Build" step is just to build, do not load the built apk yet; if you load it, it will crash since there is no native implementation for getMsgFromJni() yetGenerate the C/C++ prototype function for jni function getMsgFromJni().In MainActivity.java file, "getMsgFromJni()" is highlighed with red because Android Studio could not find its implementation; let's get it implemented:Select function "getMsgFromJni()".Wait for context aware menu prompt   to appear.Click on to bring up the popup 
         
Select "Create Function Java_com_google_example_helloandroidjni_MainActivity_getMsgFromJni".Android Studio creates a prototype function for getMsgFromJNI() in hello-android-jni.c file under the "jni" folder. Both got created at once!
#include<jni.h> JNIEXPORT jstring JNICALLJava_com_google_sample_helloandroidjni_MainActivity_getMsgFromJni(JNIEnv *env, jobject instance) {    // TODO    return (*env)->NewStringUTF(env, returnValue);}Replace "returnValue" in the above code with our own message:
// TODOreturn (*env)->NewStringUTF(env, "Hello From Jni");Display our JNI message in the application.Add an ID to the existing TextView.Open "Android Studio" pane, "res" > "layout" > "content_main.xml"[if you have chosen template "Empty Activity" in step "Create Java Sample App", you file might be "activity_main.xml" instead], select "design" view, and click or "Hello World", inside "Properties" pane, put "@+id/jni_msgView" into "ID" field:[The other way is to directly add into "text" view, and put id in with android:id="@+id/jni_msgView".]Display our jni message in the TextView.In MainActivity::onCreate() function, append following code to the end of the function:
((TextView) findViewById(R.id.jni_msgView)).setText(getMsgFromJni());Click the Run button, you should see "Hello From Jni" in your target device.Browse the Native CodeSelect "NewStringUTF" inside hello-android-jni.c, "right click" to bring up the pop-up menu.Select "Go To", and "Implementation(s)".You will see the function implementation of "NewStringUTF".Select other code to explore the native code browsing feature.
5. Debugging JNI Code
Click the Run/Debug Configuration  [For Android Studio version earlier than 2.2, select . Android Studio auto-generates this native debug configuration when it detects JNI code. In this config, debug configurations are enabled by default. If is not visible, close this project and reopen it with Android Studio, it will be there; Android Studio version 2.2 integrated the debug functionality into app configure].Open hello-android-jni.c inside Android Studio.Click the left edge of the native code to set a breakpoint:                                                                         Click the Debug button , your android device should prompt "Waiting For Debugger" message:Wait until Android Studio connects to the debugger on your device ( it might take 1 - 2 minutes, depending on the device and OS version ), and stops at the breakpoint. Click "env" inside the "Variables" window at the bottom pane of Android Studio to observe contents of env pointer.Click "+" at the bottom of the "Watches" window (next to "Variables") and add "env", Android Studio will bring the content of env into watch window. The values should be the same as the values in "Variables" window.Click the "F8" key to step over, and menu "Run" > "Resume Program" to continue the execution.
[Note: if you are using Android Studio RC 1.5 or better, you can set a breakpoint on getMsgFromJni() in Java code and "trace into" JNI code]
 项目源码 https://github.com/leon-HM/HelloAndroidJni