Android 2.3（API level 9）和Android NDK版本5支持我們使用NativeActivity類來編寫完整的活動和應用，以便能夠訪問Android應用的整個生命週期。
為了利用該方法，在Android manifest文件中引用android.app.NativeActivity。注意，引用中需要包含hasCode屬性。如果應用中沒有Java代碼，該屬性應該設置成false（只是NativeActivity）。但是，在這個例子中，因為包含Java代碼，所以我們把該屬性值設置成true：
<!-- This .apk has Java code, so set hasCode to true which is the default. -->
<!-- if this only had a native app (only the activity
called \'android.app.NativeActivity\') -->
<!-- then set to false -->
<application android:icon=\"@drawable/icon\" android:label=\"@string/app_name\"
android:hasCode=\"true\" >
<activity android:name=\".NDKApp\" android:label=\"@string/app_name\">
<intent-filter>
<action android:name=\"android.intent.action.MAIN\" />
<category android:name=\"android.intent.category.LAUNCHER\" />
</intent-filter>
</activity>
<activity android:name=\"android.app.NativeActivity\"
android:label=\"SampleNativeActivity\"
android:debuggable=\"true\" >
<!-- here we declare what lib to reference -->
<meta-data android:name=\"android.app.lib_name\"
android: />
</activity>
</application>
在這個例子中，使用頭文件android_native_app_glue.h而不使用native_activity.h頭文件，native_activity.h接口基於一組應用的回調函數，當某些事件發生時，Activity的main線程會調用這些回調函數。這表示回調函數不應該阻塞，是強制的。android_native_app_glue.h文件給出輔助庫，它包含不同的執行模式，它的方式是應用在不同的線程中實現自己的主要功能。該功能必須命名為android_main，創建應用時會調用它，並向其傳遞android_app對象。它提供了對應用或activity進行引用的機制，並能夠監聽不同的生命週期事件。
下面這個簡單的nativeactivity示例構建了一個Activity並負責監聽Motion事件。然後，會把Motion事件的x坐標和y坐標值發送給LogCat：
#include <jni.h>
#include <android/log.h>
#include <android_native_app_glue.h>
// usage of log
#define LOGINFO(x...) __android_log_print(ANDROID_LOG_INFO,\"SampleNativeActivity\",x)
// handle commands
static void custom_handle_cmd(struct android_app* app, int32_t cmd) {
switch(cmd) {
case APP_CMD_INIT_WINDOW:
LOGINFO(\"App Init Window\");
break;
}
}
// handle input
static int32_t custom_handle_input(struct android_app* app, AInputEvent* event) {
// we see a motion event and we log it
if (AInputEvent_getType(event) == AINPUT_EVENT_TYPE_MOTION) {
LOGINFO(\"Motion Event: x %f / y %f\", AMotionEvent_getX(event, 0),
AMotionEvent_getY(event, 0));
return 1;
}
return 0;
}
// This is the function that application code must implement,
// representing the main entry to the app.
void android_main(struct android_app* state) {
// Make sure glue isn\'t stripped.
app_dummy;
int events;
// set up so when commands happen we call our custom handler
state->onAppCmd = custom_handle_cmd;
// set up so when input happens we call our custom handler
state->onInputEvent = custom_handle_input;
while (1) {
struct android_poll_source* source;
// we block for events
while (ALooper_pollAll(-1, NULL, &events, (void**)&source) >= 0) {
// Process this event.
if (source != NULL) {
source->process(state, source);
}
// Check if we are exiting.
if (state->destroyRequested != 0) {
LOGINFO(\"We are exiting\");
return;
}
}
}
}
以下是示例nativeactivity的Android.mk文件。注意它加載並指向android_native_app_glue模塊：
LOCAL_PATH := $(call my-dir) # this is our sample native activity include $(CLEAR_VARS) LOCAL_MODULE := sample_native_activity LOCAL_SRC_FILES := sample_nativeactivity.c LOCAL_LDLIBS := -llog -landroid LOCAL_STATIC_LIBRARIES := android_native_app_glue include $(BUILD_SHARED_LIBRARY) $(call import-module,android/native_app_glue)
以下是當用戶啟動應用時會調用的main Java Android activity。單擊按鈕會啟動我們提供的NativeActivity：
package com.oreilly.demo.android.pa.ndkdemo;
import com.oreilly.demo.android.pa.ndkdemo.R;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
public class NDKApp extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
findViewById(R.id.nativeactivity).setOnClickListener(
new View.OnClickListener {
public void onClick(View v) {
startActivity(new Intent(getBaseContext,
android.app.NativeActivity.class)); // call nativeactivity
}
});
}
}
如果你編譯並運行過該示例，會注意到啟動本地活動時；屏幕是空白的；如果查看LogCat，會出現各種日誌信息（尤其是當在屏幕上移動手指時）。但是，這不怎麼好玩。因此，為了使界面好看些，我們需要執行一些操作。接下來給這個示例使用了OpenGL ES，可以改變屏幕的顏色。
以下是OpenGL ES的本地源代碼。當顯示活動時，會把屏幕變成亮紅色。
#include <jni.h>
#include <android/log.h>
#include <android_native_app_glue.h>
#include <EGL/egl.h>
#include <GLES/gl.h>
// usage of log
#define LOGINFO(x...)
__android_log_print(ANDROID_LOG_INFO,\"NativeWOpenGL\",x)
struct eglengine {
EGLDisplay display;
EGLSurface surface;
EGLContext context;
};
// initialize the egl engine
static int engine_init_display(struct android_app* app, struct eglengine* engine) {
const EGLint attribs = {
EGL_SURFACE_TYPE, EGL_WINDOW_BIT,
EGL_BLUE_SIZE, 8,
EGL_GREEN_SIZE, 8,
EGL_RED_SIZE, 8,
EGL_NONE
};
EGLint w, h, dummy, format;
EGLint numConfigs;
EGLConfig config;
EGLSurface surface;
EGLContext context;
EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
eglInitialize(display, 0, 0);
eglChooseConfig(display, attribs, &config, 1, &numConfigs);
eglGetConfigAttrib(display, config, EGL_NATIVE_VISUAL_ID, &format);
ANativeWindow_setBuffersGeometry(app->window, 0, 0, format);
surface = eglCreateWindowSurface(display, config, app->window, NULL);
context = eglCreateContext(display, config, NULL, NULL);
if (eglMakeCurrent(display, surface, surface, context) == EGL_FALSE) {
LOGINFO(\"eglMakeCurrent FAIL\");
return -1;
}
eglQuerySurface(display, surface, EGL_WIDTH, &w);
eglQuerySurface(display, surface, EGL_HEIGHT, &h);
engine->display = display;
engine->context = context;
engine->surface = surface;
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_FASTEST);
glEnable(GL_CULL_FACE);
glShadeModel(GL_SMOOTH);
glDisable(GL_DEPTH_TEST);
return 0;
}
// draw to the screen
static void engine_color_screen(struct eglengine* engine) {
if (engine->display == NULL) {
return;
}
glClearColor(255, 0, 0, 1); // let\'s make the screen all red
glClear(GL_COLOR_BUFFER_BIT);
eglSwapBuffers(engine->display, engine->surface);
}
// when things need to be terminated
static void engine_terminate(struct eglengine* engine) {
if (engine->display != EGL_NO_DISPLAY) {
eglMakeCurrent(engine->display, EGL_NO_SURFACE, EGL_NO_SURFACE,
EGL_NO_CONTEXT);
if (engine->context != EGL_NO_CONTEXT) {
eglDestroyContext(engine->display, engine->context);
}
if (engine->surface != EGL_NO_SURFACE) {
eglDestroySurface(engine->display, engine->surface);
}
eglTerminate(engine->display);
}
engine->display = EGL_NO_DISPLAY;
engine->context = EGL_NO_CONTEXT;
engine->surface = EGL_NO_SURFACE;
}
// handle commands
static void custom_handle_cmd(struct android_app* app, int32_t cmd) {
struct eglengine* engine = (struct eglengine*)app->userData;
switch(cmd) {
// things are starting up... let\'s initialize the engine and color the screen
case APP_CMD_INIT_WINDOW:
if (app->window != NULL) {
engine_init_display(app, engine);
engine_color_screen(engine);
}
break;
case APP_CMD_TERM_WINDOW: // things are ending...let\'s clean up the engine
engine_terminate(engine);
break;
}
}
// handle input
static int32_t custom_handle_input(struct android_app* app, AInputEvent* event) {
// we see a motion event and we log it
if (AInputEvent_getType(event) == AINPUT_EVENT_TYPE_MOTION) {
LOGINFO(\"Motion Event: x %f / y %f\", AMotionEvent_getX(event, 0),
AMotionEvent_getY(event, 0));
return 1;
}
return 0;
}
// This is the function that application code must implement,
// representing the main entry to the app.
void android_main(struct android_app* state) {
// Make sure glue isn\'t stripped.
app_dummy;
// here we add the eglengine to the app
struct eglengine engine;
memset(&engine, 0, sizeof(engine));
// set engine as userdata so we can reference
state->userData = &engine;
int events;
// set up so when commands happen we call our custom handler
state->onAppCmd = custom_handle_cmd;
// set up so when input happens we call our custom handler
state->onInputEvent = custom_handle_input;
while (1) {
struct android_poll_source* source;
// we block for events
while (ALooper_pollAll(-1, NULL, &events, (void**)&source) >= 0) {
// Process this event.
if (source != NULL) {
source->process(state, source);
}
// Check if we are exiting.
if (state->destroyRequested != 0) {
LOGINFO(\"We are exiting\");
return;
}
}
}
}
sample_native_activity_opengl活動的Android.mk文件會加載EGL和GLESv1_CM庫：
LOCAL_PATH := $(call my-dir) # this is our sample native activity with opengl include $(CLEAR_VARS) LOCAL_MODULE := sample_native_activity_opengl LOCAL_SRC_FILES := sample_nativeactivity_opengl.c # loading the log , android, egl, gles libraries LOCAL_LDLIBS := -llog -landroid -lEGL -lGLESv1_CM LOCAL_STATIC_LIBRARIES := android_native_app_glue include $(BUILD_SHARED_LIBRARY) $(call import-module,android/native_app_glue)