Android JNI entry instance (Windows + cygwin + eclipse)

1 Basic Knowledge Point

① JNI: Java Native Interface
② Call JNI in Android:

The Code declared in the static // static area is executed before the oncreate method.

{

System. loadlibrary ("helloworld"); // load. The complete name is lib helloworld. So.

}

Private native string Hello (); // has the native keyword

2. Basic Steps for JNI Development

① Write. Java class
② Generate a. Class File
③ Generate a. h file
③ Check. h file

Jniexport and jnicall are JNI macros.

Note signature before the function: () ljava/lang/string; brackets in the meaning: indicates that the function parameter is null, ljava/lang/string indicates that the function return value is a string object of Java
④ Compile the. c/CPP File
⑤ Create the Android. mk file (same directory as the. c file)
⑥ Compile and generate the. So file

Borrow an image from the Refs-8, as shown below

3. Example: testjni ([cygwin] in windows, for the Linux environment, please refer to the article in refs) ① create an android project and compile the testjni. Java class. The source code is as follows:

 1 package com.testjni;
 2 
 3 import android.app.Activity;
 4 import android.os.Bundle;
 5 import android.util.Log;
 6 
 7 public class TestJNI extends Activity
 8 {
 9     /** Called when the activity is first created. */
10     @Override
11     public void onCreate(Bundle savedInstanceState)
12     {
13         super.onCreate(savedInstanceState);
14         setContentView(R.layout.main);
15         Log.d("Hi", "Android call JNI: " + outputJNI());
16     }
17     
18     private native String outputJNI();
19     
20     static
21     {
22         System.loadLibrary("testjni");
23     }
24 }

② Compile and generate the testjni. Class File

Compilation Method:

Method 1: Click build project under android to generate the corresponding. Class file under the binfile of the project.

Method 2: Run cmd, locate the project directory, and run the javac command.

③ Compile and generate the com_testjni_testjni.h File

Shows the compilation method. The first three red boxes are common errors. Please note!

④ Compile the. c file.

You can write it directly in Notepad. Of course, if your eclipse environment has been integrated with the C/C ++ Development Environment (For details, refer to [Android tutorial] To build android.
Ndk environment), which can be directly written in eclipse

The Code is as follows. For the description, see the notes:

⑤ Create the Android. mk file (same directory as the. c file)

 

6 compile and generate the libtestjni. So file

Compilation Method:

Open cygwin (for cygwin installation, see [Android tutorial] to build the android ndk Environment). Run the following command:

Note:

I copied the project to the ndk configuration environment directory to run it. I can say that I can directly CD it to the current project directory, and then run it. I tried it n times and failed, my project is under D: \ My document (ndk is in c: \ Android \ android-ndk-r7)

The running result is as follows:

Refs/related

1 http://my.unix-center.net /~ Simon_fu /? P = 833

2 http://my.unix-center.net /~ Simon_fu /? P = 836

3 http://www.android123.com.cn/androidkaifa/679.html

4 http://doandroid.info/2012/03/18/jni_and_android_jni_details/

Http://blog.csdn.net/hellogv/article/details/6094127

Http://blog.csdn.net/redoffice/article/details/6654714

7 http://www.cnblogs.com/lilactutu/archive/2010/12/06/1897696.html

8 http://my.unix-center.net /~ Simon_fu /? P = 359

Author: skyseraph

Source: http://www.cnblogs.com/skyseraph/

Email/Gtalk: zgzhaobo@gmail.com

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