安卓NDK开发之快速熟悉JNI参数的回调

前言：在上一节中我们介绍了通过java传递参数给JNI，今天我们熟悉一下JNI的回调，java访问jni，然后通过类反射的方式拿到java的方法，来实现回调。

----------分割线------

在jni系列中有讲到：《JNI开发之调用java实力类父类的方法》

---------分割线-----

今天我们就在安卓的NDK开发快速实现一下几个demo：

---------分割线------

开始撸代码：java代码：

MainActivity.java:

package com.fly.demo4;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Toast;public class MainActivity extends AppCompatActivity {    private JNI jni;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        jni = new JNI(this);    }    public void callbackvoidmethod(View view) {        jni.callbackvoidmethod();    }    public void callbackintmethod(View view) {        Toast.makeText(this, "" + jni.callbackintmethod(), Toast.LENGTH_SHORT).show();    }    public void callbackstringmethod(View view) {        jni.callbackStringmethod();    }    public void callbacktoastmethod(View view) {        jni.callbackShowToast();    }}

JNI.java:

package com.fly.demo4;import android.content.Context;import android.widget.Toast;/** * Created by Fly on 2017/7/6. */public class JNI {    static {        System.loadLibrary("native-lib");    }    private Context mContext;    public JNI(Context context) {        mContext = context;    }    public native void callbackvoidmethod();    public native int callbackintmethod();    public native void callbackStringmethod();    public native void callbackShowToast();    //C调用java空方法    public void helloFromJava() {        Toast.makeText(mContext, "hello from java", Toast.LENGTH_SHORT).show();    }    //C调用java中的带两个int参数的方法    public int add(int x, int y) {        return x + y;    }    //C调用java中参数为string的方法    public void printString(String s) {        Toast.makeText(mContext, s, Toast.LENGTH_SHORT).show();    }    public void showToast(String s) {        Toast.makeText(mContext, s, Toast.LENGTH_SHORT).show();    }}

C代码：

#include <jni.h>#include <stdlib.h>#include <stdio.h>/* * Class:     com_fly_demo4_JNI * Method:    callbackvoidmethod * Signature: ()V * 回调空方法 */JNIEXPORT void JNICALL Java_com_fly_demo4_JNI_callbackvoidmethod        (JNIEnv *env, jobject clazz) {    //1.获取字节码对象    jclass claz = (*env)->FindClass(env, "com/fly/demo4/JNI");    //2.获取Method对象    jmethodID methodID = (*env)->GetMethodID(env, claz, "helloFromJava", "()V");    //3.通过字节码对象创建一个Object    //4.通过对象调用方法    (*env)->CallVoidMethod(env, clazz, methodID);}/* * Class:     com_fly_demo4_JNI * Method:    callbackintmethod * Signature: ()V * 回调int方法 */JNIEXPORT jint JNICALL Java_com_fly_demo4_JNI_callbackintmethod        (JNIEnv *env, jobject clazz) {    jclass claz = (*env)->FindClass(env, "com/fly/demo4/JNI");    jmethodID methodID = (*env)->GetMethodID(env, claz, "add", "(II)I");    int result = (*env)->CallIntMethod(env, clazz, methodID, 10, 20);    return result;}/* * Class:     com_fly_demo4_JNI * Method:    callbackStringmethod * Signature: ()V * 回调String方法 */JNIEXPORT void JNICALL Java_com_fly_demo4_JNI_callbackStringmethod        (JNIEnv *env, jobject clazz) {    jclass claz = (*env)->FindClass(env, "com/fly/demo4/JNI");    jmethodID methodID = (*env)->GetMethodID(env, claz, "printString", "(Ljava/lang/String;)V");    jstring result = (*env)->NewStringUTF(env, "Hello from c");    (*env)->CallVoidMethod(env, clazz, methodID, result);}/* * Class:     com_fly_demo4_JNI * Method:    callbackShowToast * Signature: ()V * 回调Toast */JNIEXPORT void JNICALL Java_com_fly_demo4_JNI_callbackShowToast        (JNIEnv *env, jobject clazz) {    jclass claz = (*env)->FindClass(env, "com/fly/demo4/JNI");    jmethodID methodid = (*env)->GetMethodID(env, claz, "showToast", "(Ljava/lang/String;)V");    //jobject     (*AllocObject)(JNIEnv*, jclass);    //通过字节码对象创建 java对象 在这儿就是创建了mainactivity的对象    //jobject obj =(*env)->AllocObject(env,claz);    jstring result = (*env)->NewStringUTF(env, "hello from c2");    //void        (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);    (*env)->CallVoidMethod(env, clazz, methodid, result);}

简单的布局：

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:app="http://schemas.android.com/apk/res-auto"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical"    tools:context="com.fly.demo4.MainActivity">    <Button        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:onClick="callbackvoidmethod"        android:text="回调空方法" />    <Button        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:onClick="callbackintmethod"        android:text="回调int参数方法" />    <Button        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:onClick="callbackstringmethod"        android:text="回调string参数方法" />    <Button        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:onClick="callbacktoastmethod"        android:text="回调Toast方法" /></LinearLayout>

--------完-------