<span style="font-family: Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255);">一、首先是几个重要的方法:</span>
//全局的变量,用来记录java中的类/对象/方法ID
jclass m_class;
jobject m_object;
jmethodID m_mid_static,m_mid;
//得到传入对象所对应的类
jclass clazz=(*env)->GetObjectClass(env,jobject);
//得到全局可用的类,
m_class=(jclass)(*env)->NewGlobalRef(env,jclass);
//得到全局可用的对象
m_object=(jobject)(*env)->NewGlobalRef(env,jobject);
//得到java中静态方法的id,后面的2个参数为在java中的方法名、方法中参数的类型(后面举例说明)
m_mid_static=(*env)->GetStaticMethodID(env,m_class,"method_name_in_java","args");
//得到java中方法的id.....
m_mid=(*env)->GetMethodID(env,m_class,"method_name_in_java","args");
//执行java中静态的空返回值的类型的方法,因为是静态方法,所以要指定java类,方法id以及要传入的参数
(*env)->CallStaticVoidMethod(env,m_class,m_mid_static,args...);
//执行java中空返回值类型的方法,需要传入java对象,方法id以及要传入的参数
(*env)->CallVoidMethod(env,m_object,m_mid,args...);
二、示例代码
native代码类:
package com.aii.ndk; import android.app.Activity; import android.os.Handler; import android.os.Message; public class CounterNative { <span style="white-space:pre"> </span>public static Handler handler; <span style="white-space:pre"> </span>public CounterNative(final Activity activity) { <span style="white-space:pre"> </span>handler = new Handler() { <span style="white-space:pre"> </span>@Override <span style="white-space:pre"> </span>public void handleMessage(Message msg) { <span style="white-space:pre"> </span>activity.setTitle(msg.obj.toString()); <span style="white-space:pre"> </span>} <span style="white-space:pre"> </span>}; <span style="white-space:pre"> </span>// 初始化该类的时候,在本地方法执行初始化,具体内容是:将当前对象,类,方法等记录在c的全局变量中 <span style="white-space:pre"> </span>nativeSetup(); <span style="white-space:pre"> </span>} <span style="white-space:pre"> </span>static { <span style="white-space:pre"> </span>//加载库 <span style="white-space:pre"> </span>System.loadLibrary("CCallJava"); <span style="white-space:pre"> </span>} <span style="white-space:pre"> </span>//由c语言回调的方法,一旦回调,则发送信息给主线程的looper,要求改变UI <span style="white-space:pre"> </span>public static void setValue(int value) { <span style="white-space:pre"> </span>Message msg = Message.obtain(); <span style="white-space:pre"> </span>msg.obj = value; <span style="white-space:pre"> </span>handler.sendMessage(msg); <span style="white-space:pre"> </span>} <span style="white-space:pre"> </span>//同上 <span style="white-space:pre"> </span>public void setV(int value) { <span style="white-space:pre"> </span>Message msg = Message.obtain(); <span style="white-space:pre"> </span>msg.obj = value; <span style="white-space:pre"> </span>handler.sendMessage(msg); <span style="white-space:pre"> </span>} <span style="white-space:pre"> </span> <span style="white-space:pre"> </span>public native void nativeSetup(); <span style="white-space:pre"> </span>public static native void nativeExecute(int n); <span style="white-space:pre"> </span>public native void nativeExec(int n); }
package com.example.ccalljava; import com.aii.ndk.CounterNative; import android.os.Bundle; import android.support.v7.app.ActionBarActivity; import android.view.View; public class MainActivity extends ActionBarActivity { private CounterNative cNative; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); // 初始化对象 cNative = new CounterNative(this); } // 该方法由UI上的的按钮触发 public void staticClick(View view) { // 调用本地方法, CounterNative.nativeExecute(10); } // 该方法由UI上的的按钮触发 public void click(View view) { // 调用本地方法, cNative.nativeExec(100); } }
#include "com_aii_ndk_CounterNative.h" #include<android/log.h> //记录类对象 jclass m_class; //记录对象对象 jobject m_object; //记录方法id jmethodID m_mid_static, m_mid; /*这段注释是.h文件中自动生成拷过来的,其中的signature经过测试。。()V表示的应该是无参方法。(I)V表示的应该是参数的额1个int的方法,,,猜的 * Class: com_aii_ndk_CounterNative * Method: nativeSetup * Signature: ()V * */JNIEXPORT void JNICALL Java_com_aii_ndk_CounterNative_nativeSetup(JNIEnv *env, <span style="white-space:pre"> </span>jobject thiz) { <span style="white-space:pre"> </span>//传过来的是jobject类型对象,现在要得到jclass类型, <span style="white-space:pre"> </span>jclass clazz = (*env)->GetObjectClass(env, thiz); <span style="white-space:pre"> </span>//得到全局可用的 <span style="white-space:pre"> </span>m_class = (jclass) (*env)->NewGlobalRef(env, clazz); <span style="white-space:pre"> </span>//得到全局可用的 <span style="white-space:pre"> </span>m_object = (jobject) (*env)->NewGlobalRef(env, thiz); <span style="white-space:pre"> </span>//得到方法的id <span style="white-space:pre"> </span>m_mid_static = (*env)->GetStaticMethodID(env, m_class, "setValue", "(I)V"); <span style="white-space:pre"> </span>m_mid = (*env)->GetMethodID(env, m_class, "setV", "(I)V"); } /* * Class: com_aii_ndk_CounterNative * Method: nativeExecute * Signature: (I)V * * */JNIEXPORT void JNICALL Java_com_aii_ndk_CounterNative_nativeExecute( <span style="white-space:pre"> </span>JNIEnv *env, jclass clazz, jint arg) { <span style="white-space:pre"> </span>//调用静态的方法,肯定得知道方法所属的字节码,方法的id(这里的唯一标识用这个表示),方法的参数,然后通过这个*env去虚拟机找去 <span style="white-space:pre"> </span>(*env)->CallStaticVoidMethod(env, clazz, m_mid_static, arg); } /* * Class: com_aii_ndk_CounterNative * Method: nativeExec * Signature: (I)V * * */JNIEXPORT void JNICALL Java_com_aii_ndk_CounterNative_nativeExec(JNIEnv *env, <span style="white-space:pre"> </span>jobject obj, jint arg) { <span style="white-space:pre"> </span>(*env)->CallVoidMethod(env, obj, m_mid, arg); }
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" > <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/hello_world" /> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:onClick="staticClick" android:text="static method" /> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:onClick="click" android:text="method" /> </LinearLayout>