Javaでjniインタフェースでnative codeを呼び出す
native code so ， Java JNI native code 。 ， Android java code native code。 1 android project, Why 2 Why Java ，class Jni。 JNI Java ， Jni.java。 package com.yarin.android.Why; public class Jni {
public native int getCInt();
public native String getCString(); } 3 Why "src\com\yarin\android\Why" Jni.java copy “Why\bin\classes” .4 Generate Jni.class file via the command below: javac jni.java Then copy the Jni.class file generated to cover and replace the original Jni.class file in directory “Why\bin\classes\com\yarin\android\Why”. ------The original Jni.class file, you must build the java project first to generate it. 5 Generate c style header file javah –classpath C:\android-ndk-r6b\myproject\Why\bin\classes com.yarin.android.Why.Jni com.yarin.android.Why is my package name appeared in Jni.java file. com_yarin_android_Why_Jni.h is like below: /* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_yarin_android_Why_Jni */#ifndef _Included_com_yarin_android_Why_Jni
#define _Included_com_yarin_android_Why_Jni
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: com_yarin_android_Why_Jni
* Method: getCInt
* Signature: ()I
*/
JNIEXPORT jint JNICALL Java_com_yarin_android_Why_Jni_getCInt
(JNIEnv *env, jobject object); ---you need to supplement the parameter name yourself/*
* Class: com_yarin_android_Why_Jni
* Method: getCString
* Signature: ()Ljava/lang/String;
*/
JNIEXPORT jstring JNICALL Java_com_yarin_android_Why_Jni_getCString
(JNIEnv *env, jobject object);#ifdef __cplusplus
}
#endif
#endif 6 Add com_yarin_android_Why_Jni.c file corresponding to the above c style header file, then add implemented code.
#include
int add() { int x,y; x = 111; y = 22; x += y;
return x; }
JNIEXPORT jint JNICALL Java_com_yarin_android_Why_Jni_getCInt (JNIEnv *env, jobject object) { return add(); }
JNIEXPORT jstring JNICALL Java_com_yarin_android_Why_Jni_getCString (JNIEnv *env, jobject object) { (*env)->NewStringUTF(env, "Why is ok ^_^ ----->> "); }
7その後、プロジェクトWhyの下でディレクトリjniを作成し、copy com_を実現する.yarin_android_Why_Jni.c/hはjniディレクトリの下にあります.
8「Whyjni」ディレクトリでAndroid.mkを作成し、「android-ndk-r 6 bjni」でApplication.mkを作成し、NDK環境でnative codeをコンパイルし、ダイナミックライブラリlibWhy.soを生成します.これはあなたがすでに前編から知っている.......
9 Javaエンジニアリングにnativeダイナミックライブラリを呼び出すコードを追加します.
package com.yarin.android.Why;
import android.app.Activity; import android.os.Bundle; import android.widget.TextView;
public class WhyActivity extends Activity { static { System.loadLibrary("Why"); } /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Jni jni = new Jni(); TextView view = new TextView(this); view.setText(jni.getCString() + Integer.toString(jni.getCInt())); setContentView(view); } }
10 Whyエンジニアリングをコンパイルし、run as Androidアプリケーションを使用すると、native codeの呼び出し結果が表示されます.
Tip:
Usage of the command javah.
javah -d
where:
'outputdir' is the directory where to put the generated header file
'classpath' contains an absolute path to the directory containing your root package (as mentionned by Glen)
'fully_qualified_class' is the name of the class containing native methods without .class extension
-jni option is not required (set by default)