1.创建xxx.jni包并在该包下实现一些Java的方法，和要调用的本地方法
2.实现MainActivity中的按钮点击事件—即点击按钮调用本地的方法
3.在C文件中的方法中回调Java的方法
3.1：通过env获取字节码对象—>jclass (*FindClass)(JNIEnv*, const char*)
第二个参数为要回调Java方法所在类的全路径如：jclass claz = (*env)->FindClass(env, "com/rocky/jniccallbackdemo/jni/JNI");
3.2：通过字节码对象获取方法ID—>jmethodID (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);
第二个参数是由3.1获取的字节码对象，第三个对象是要回调的Java方法名，第四个参数该Java方法签名，因为Java中有重载，需要此参数确定具体是哪个方法如：jmethodID methodId = (*env)->GetMethodID(env, claz, "helloFromJava", "()V")
注：对应方法签名，需要到工程目录下的bin/classes目录下执行：javap -s com.rocky.jniccallbackdemo.jni.JNI（该方法所在类的全类名）
3.3：通过字节码对象创建Java对象—>jobject (*AllocObject)(JNIEnv*, jclass);
如：jobject obj = (*env)->AllocObject(env, claz);
注：如果本地方法和要回调的Java方法在同一个类中，则第二参数就是本地方法传过来的第二个参数，即第三步可以可以省略。
3.4：通过Java对象回调Java方法
调用Java的无返回值方法：void (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...)，如： (*env)->CallVoidMethod(env, clazz, methodId);
DEMO:
JNI.java
public class JNI
{
static {
System.loadLibrary("callback");
}
private Context mContext = null;
public JNI(Context context)
{
this.mContext = context;
}
public void helloFromJava()
{
System.out.println("Hello From Java");
}
public void printString(String str)
{
System.out.println(str);
}
public void showToast(String str)
{
Toast.makeText(mContext, str, Toast.LENGTH_SHORT).show();
}
public native void callbackVoidMethod();
public native void callbackStringMethod();
public native void callbackIntMethod();
public native void callbackShowToastMethod();
}
MainActivity.java
public class MainActivity extends Activity implements OnClickListener
{
Context mContext = null;
Button bt_callback_void = null;
Button bt_callback_string = null;
Button bt_callback_int = null;
Button bt_callback_toast = null;
JNI jni = null;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mContext = this;
jni = new JNI(mContext);
bt_callback_void = (Button) findViewById(R.id.bt_callback_void);
bt_callback_void.setOnClickListener(this);
bt_callback_int = (Button) findViewById(R.id.bt_callback_int);
bt_callback_int.setOnClickListener(this);
bt_callback_string = (Button) findViewById(R.id.bt_callback_string);
bt_callback_string.setOnClickListener(this);
bt_callback_toast = (Button) findViewById(R.id.bt_callback_toast);
bt_callback_toast.setOnClickListener(this);
}
public int add(int x, int y)
{
return x + y;
}
@Override
public void onClick(View v)
{
switch (v.getId())
{
case R.id.bt_callback_void:
jni.callbackVoidMethod();
break;
case R.id.bt_callback_int:
jni.callbackIntMethod();
break;
case R.id.bt_callback_string:
jni.callbackStringMethod();
break;
case R.id.bt_callback_toast:
jni.callbackShowToastMethod();
break; default:
break;
}
}
}
callback.c
#include <jni.h>
#include <android/log.h>
#define LOG_TAG "rocky"
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, __VA_ARGS__)
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, __VA_ARGS__)
#define LOGW(...) __android_log_print(ANDROID_LOG_WARN, LOG_TAG, __VA_ARGS__)
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)
#define LOGV(...) __android_log_print(ANDROID_LOG_VERBOSE, LOG_TAG, __VA_ARGS__) JNIEXPORT void JNICALL Java_com_rocky_jniccallbackdemo_jni_JNI_callbackVoidMethod
(JNIEnv *env, jobject clazz)
{
//1.获取字节码对象 jclass (*FindClass)(JNIEnv*, const char*);
jclass claz = (*env)->FindClass(env, "com/rocky/jniccallbackdemo/jni/JNI");
//2.通过字节码对象获取方法ID jmethodID (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);
jmethodID methodId = (*env)->GetMethodID(env, claz, "helloFromJava", "()V");
//3.通过字节码对象创建Java对象(此处因为本地方法和回调方法在同一个类中，可以省略)
//4.通过Java对象回调Java方法 void (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);
(*env)->CallVoidMethod(env, clazz, methodId);
}
/*
* Class: com_rocky_jniccallbackdemo_jni_JNI
* Method: callbackIntMethod
* Signature: ()V
*/
JNIEXPORT void JNICALL Java_com_rocky_jniccallbackdemo_jni_JNI_callbackIntMethod
(JNIEnv *env, jobject clazz)
{
jclass claz = (*env)->FindClass(env, "com/rocky/jniccallbackdemo/MainActivity");
jmethodID methodId = (*env)->GetMethodID(env, claz, "add", "(II)I");
//3.通过字节码对象创建Java对象(此处为MainActivity对象） jobject (*AllocObject)(JNIEnv*, jclass);
// jobject obj = (*env)->AllocObject(env, claz);
//4.通过Java对象回调Java方法 void (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);
jobject obj = (*env)->AllocObject(env, claz);
jint res = (*env)->CallIntMethod(env, obj, methodId, , );
LOGI("res = %d\n", res);
}
JNIEXPORT void JNICALL Java_com_rocky_jniccallbackdemo_jni_JNI_callbackStringMethod
(JNIEnv *env, jobject clazz)
{
jclass claz = (*env)->FindClass(env, "com/rocky/jniccallbackdemo/jni/JNI");
jmethodID methodId = (*env)->GetMethodID(env, claz, "printString", "(Ljava/lang/String;)V");
jstring result = (*env)->NewStringUTF(env, "cccccccccccccc");
(*env)->CallVoidMethod(env, clazz, methodId, result);
}
JNIEXPORT void JNICALL Java_com_rocky_jniccallbackdemo_jni_JNI_callbackShowToastMethod
(JNIEnv *env, jobject clazz)
{
jclass claz = (*env)->FindClass(env, "com/rocky/jniccallbackdemo/jni/JNI");
jmethodID methodId = (*env)->GetMethodID(env, claz, "showToast", "(Ljava/lang/String;)V");
jstring result = (*env)->NewStringUTF(env, "rocky--------rocky");
(*env)->CallVoidMethod(env, clazz, methodId, result);
}
Android.mk
LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) LOCAL_MODULE := callback
LOCAL_SRC_FILES := callback.c LOCAL_LDLIBS += -llog include $(BUILD_SHARED_LIBRARY)