Android移植---JNI中HelloWorld的C和C++实现

最新推荐文章于 2021-03-07 23:52:39 发布

YasinEmb

最新推荐文章于 2021-03-07 23:52:39 发布

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分类专栏： Android

本文链接：https://blog.youkuaiyun.com/yixuaning/article/details/18838459

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本文详细介绍了如何在Android中使用JNI技术，通过C和C++实现HelloWorld示例，讲解了关键步骤和代码实现。

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MainActivity.java

package com.example.jniload;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.widget.TextView;

public class MainActivity extends Activity {

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		TextView  tv = new TextView(this);
        tv.setText( stringFromJNI() );
        setContentView(tv);
		//setContentView(R.layout.activity_main);
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}
	native String stringFromJNI();
	static{
		System.loadLibrary("jniload");
	}
}

test-jni.c

#include <jni.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>

# define NELEM(x) ((int) (sizeof(x) / sizeof((x)[0])))
#define JNIREG_CLASS "com/example/test/Test"

JNIEXPORT jstring JNICALL stringFromJNI(JNIEnv *env, jclass clazzi)
{
    return (*env)->NewStringUTF(env, "hello Android3.");
}

static JNINativeMethod method_table[] = {
    { "stringFromJNI", "()Ljava/lang/String;", (void*)stringFromJNI },//绑定
};

static int registerNativeMethods(JNIEnv* env, const char* className,
        JNINativeMethod* gMethods, int numMethods)
{
    jclass clazz;
    clazz = (*env)->FindClass(env, className);
    if (clazz == NULL) {
        return JNI_FALSE;
    }
    if ((*env)->RegisterNatives(env, clazz, gMethods, numMethods) < 0) {
        return JNI_FALSE;
    }

    return JNI_TRUE;
}

int register_ndk_load(JNIEnv *env)
{
    return registerNativeMethods(env, JNIREG_CLASS,
            method_table, NELEM(method_table));
}

JNIEXPORT jint JNI_OnLoad(JavaVM* vm, void* reserved)
{
    JNIEnv* env = NULL;
    jint result = -1;

    if ((*vm)->GetEnv(vm, (void**) &env, JNI_VERSION_1_4) != JNI_OK) {
        return result;
    }

    register_ndk_load(env);

    return JNI_VERSION_1_4;
}

jni-load.cpp

#include <jni.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#define NELEM(x) ((int) (sizeof(x) / sizeof((x)[0])))
#define JNIREG_CLASS "com/example/jniload/MainActivity"

extern "C"

/*jstring Java_com_example_jniload_MainActivity_stringFromJNI( JNIEnv* env,jobject thiz )
{
	char* str="Hello from JNI.";
	return (env)->NewStringUTF(str);
}*/
JNIEXPORT jstring JNICALL stringFromJNI( JNIEnv* env,jobject thiz )
{
	char* str="Hello from JNI.";
	return (env)->NewStringUTF(str);
}

static JNINativeMethod method_table[] = {
    { "stringFromJNI", "()Ljava/lang/String;", (void*)stringFromJNI },
};

static int registerNativeMethods(JNIEnv* env, const char* className,
        JNINativeMethod* gMethods, int numMethods)
{
    jclass clazz;
    clazz = env->FindClass(className);
    if (clazz == NULL) {
        return JNI_FALSE;
    }
    if (env->RegisterNatives(clazz, gMethods, numMethods) < 0) {
        return JNI_FALSE;
    }

    return JNI_TRUE;
}

int register_ndk_load(JNIEnv *env)
{
   return registerNativeMethods(env, JNIREG_CLASS, method_table, NELEM(method_table));
}

jint JNI_OnLoad(JavaVM* vm, void* reserved)
{
    JNIEnv* env = NULL;
    jint result = -1;

    if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) {
    	return result;
	}
    //result=register_ndk_load(env);

    if ( register_ndk_load(env) < 0){
    	goto bail;
    }
    result = JNI_VERSION_1_4;

bail:
    return result;
}