图解 android 4.0 jni Hello World 开发

鉴客 发布于 2011/11/21 11:41
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之前之前用R4,现在一下就跳到用R7了,ANDROID4.0出来过后,应该有不少热机友敢望资疗吧,OK,在网上偶尔浏览的时候,看到有很多初学者希望了解在ANDROID中NDK应用的开发,不知道它是怎么开发与运行的,今天我就简单来图解一个HelloWorld的简单实列吧,以好供初学者做给力的参考,OK,不废话了,直入正题吧:

首先,我们得配置环境,当然这是在你本来就有SDK开发环境的情况下,请去官方下个NDK吧:http://www.android.com.

最新版本为android-ndk-r7-linux-x86.tar.bz2,即R7,我一直用的是LINUX,所以我下的是LINUX版本,如果你是WINDOWS或者MAC的话,你自己看着办吧,OK,下下来后,解压在你自己认为可以放的地方就行了,看目录:

,以上为解压后的R7目录,先别急新建项目开发,先配置NDK环境:打开终端,输入命令:sudo vim ~/.baserc,打开后根据下面图,填入下下来的NDK目录路径:

 

在图中可以看到有这行:export NDK_HOME=/home/development/android/android-ndk-r7/

即为NDK所需配置的环境路径。保存后,输入: source ~/.baserc 来使其配置立即生效,OK后,咋们来新创建一个项目,为jni_demo,下面我需要看当前那个目录截图,你会发现目录中有一个sample目录,里面就是其本身已有的列子,在这里我得提醒各位,不敢你遇到任何新的语言,先看它的Hello World列子,不要急于误打误撞的敲代码,先看清楚它的列子的运行效果,OK,在这里我们就以hello-jni这个列子来验证吧,打开这个目录:

可看到有四个目录,一个是JNI为C~比源码处,一个是APP的RES,一个SRC为JAVA源代码,再一个就是测试目录,另外两个文件就不在这里说了,我们新建了项目后,需要写JNI代码与JAVA代码,所以在这里,我就直接把这里的jni里面的代码拷贝到我的项目中去,记得在自己的项目中需要新建一个 jni文件,其拷贝的两个文件分别是:Android.mk与hello-jni.c,其Android.mk文件内容是:

# Copyright (C) 2009 The Android Open Source Project
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
LOCAL_PATH := $(call my-dir)


include $(CLEAR_VARS)


LOCAL_MODULE    := hello-jni
LOCAL_SRC_FILES := hello-jni.c


include $(BUILD_SHARED_LIBRARY)


hello-jni.c文件的内容为:

/*
 * Copyright (C) 2009 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */
#include <string.h>
#include <jni.h>


/* This is a trivial JNI example where we use a native method
 * to return a new VM String. See the corresponding Java source
 * file located at:
 *
 *   apps/samples/hello-jni/project/src/com/example/HelloJni/HelloJni.java
 */
jstring
Java_com_jsd_jni_demo_JsdJniActivity_getJniDatas
( JNIEnv* env,
                                                  jobject thiz )
{
    return (*env)->NewStringUTF(env, "This is for Datas from JNI !");
}

注意观察红色字体,其为项目目录路径地址,根据自己实际项目目录来定,

好了,在新建ACTIVITY类中:

package com.jsd.jni.demo;


import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;


/**
 * 
 * @author jankey
 *
 */
public class JsdJniActivity extends Activity {

private Button mJniDemo = null;
private TextView mGetJni = null;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        findById();
    }
    
    private void findById(){
    mJniDemo = (Button) findViewById(R.id.jniDemo);
    mGetJni = (TextView) findViewById(R.id.getJni);
    mJniDemo.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
mGetJni.setText(getJniDatas());
}
});
    }
    
    /**
     * A native method that is implemented by the 
     * 'hello-jni' native library, which is packaged
     * with this application.
     * @return
     */
    public native String getJniDatas();
    
    /**
     *This is another native method declaration that is *not*
     * implemented by 'hello-jni'. This is simply to show that
     * you can declare as many native methods in your Java code
     * as you want, their implementation is searched in the
     * currently loaded native libraries only the first time
     * you call them.
     *
     * Trying to call this function will result in a
     * java.lang.UnsatisfiedLinkError exception !
     * @return
     */
    public native String unimplementedGetJniDatas();
    
    /**
     * this is used to load the 'hello-jni' library on application
     * startup. The library has already been unpacked into
     * /data/data/com.example.HelloJni/lib/libhello-jni.so at
     * installation time by the package manager.
     */
    static{
    System.loadLibrary("hello-jni");
    }   
}

上面有注释,其native方法为JNI需要调用与执行的方法,

在布局里就添加了一个按钮与一个文本,使用按钮单点后来获得文本显示的字符为JNI所得来的数据,其实这个过程很简单,基本就是NDK里面本身的列子般过来运行一样,等这都完了,先不要急于运行,你需要先把C文件进行编译后才能执行运行APP,在命令行进入其目录的JNI目录,使用ndk-build命令来构建编译:

你会看到:jankey@jankey-ThinkPad-Edge:~/workspace/jni_demo/jni$ ndk-build 
Compile thumb  : hello-jni <= hello-jni.c
SharedLibrary  : libhello-jni.so
Install        : libhello-jni.so => libs/armeabi/libhello-jni.so,生成了两个文件目录:

即两个.so为后缀的文件,在这里基本就没什么问题了,这样就建立了C与JAVA通信的一个过程,OK,使用CTRI+F11开始运行其APP:

,先我们可以单击来获取JNI返回回来的数据了:


 

就把数据给调出来了,如果你是初学者,你还等什么呢,赶快动手吧,希望这能给在入门里做最给里的参考,谢谢,有时间,我会继续慢慢的写一些深入的内容,可敬请期待

文章出处:http://blog.csdn.net/jiangshide/article/details/6993133

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0
duty
duty
mark 备用。。
0
wubotao
wubotao
马克。。。
0
李紫阳
李紫阳
这个还不错。。
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