架构基础（一）---AOP面向切面架构设计

什么是AOP面向切面架构设计？

Android 4.0 以后 Google 推出了 ActivityLifecycleCallbacks接口就是AOP面向切面架构设计的。

简单使用介绍如下：能监听应用每个activity的生命周期。

public class myApp extends Application {

    @Override
    public void onCreate() {
        super.onCreate();
        registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks() {
            @Override
            public void onActivityCreated(Activity activity, Bundle bundle) {
                Log.d("mile",activity.getComponentName().getClassName() +  "onActivityCreated");
            }

            @Override
            public void onActivityStarted(Activity activity) {

            }

            @Override
            public void onActivityResumed(Activity activity) {

            }

            @Override
            public void onActivityPaused(Activity activity) {

            }

            @Override
            public void onActivityStopped(Activity activity) {

            }

            @Override
            public void onActivitySaveInstanceState(Activity activity, Bundle bundle) {

            }

            @Override
            public void onActivityDestroyed(Activity activity) {

            }
        });
    }

实现一个简单数据库面向切面架构设计

场景如下：操作数据库“增删改”前需要先备份一下， 由于 增加、删除、修改都需要去备份一下，这里我们就可以使用切面架构设计思想来完成。核心是动态代理

创建一个数据库操作接口

/**
 * Created by mile on 2019/9/15.
 */

public interface DBHelper {

    void insert();

    void delete();

    void update();

    //数据备份
    void save();
}

在MainActivity中实现该接口，只是个例子一般情况下不是Activity来实现这个接口

public class MainActivity extends AppCompatActivity implements DBHelper {

    private static final String TAG = "MainActivity";
    private DBHelper db;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        db = (DBHelper) Proxy.newProxyInstance(DBHelper.class.getClassLoader(),new Class[]{DBHelper.class},
                new DBHandler(this));
    }

	private class DBHandler implements InvocationHandler {
        private DBHelper db;
        public DBHandler(DBHelper db) {
            this.db = db;
        }

        @Override
        public Object invoke(Object o, Method method, Object[] objects) throws Throwable {
            if (db != null){
                Log.d(TAG,"操作数据库前------");
                save();
                Log.d(TAG,"备份成功------");
                return method.invoke(db,objects);
            }
            return null;
        }
    }

    @Override
    public void insert() {
        Log.d(TAG,"插入数据---------------------------");
    }

    @Override
    public void delete() {
        Log.d(TAG,"删除数据---------------------------");
    }

    @Override
    public void update() {
        Log.d(TAG,"更新数据---------------------------");
    }

    @Override
    public void save() {
        Log.d(TAG,"保存数据---------------------------");
    }

//点击删除按钮
    public void delete(View view) {
        db.delete();
    }

    
}

核心代码如下：

db = (DBHelper) Proxy.newProxyInstance(DBHelper.class.getClassLoader(),new Class[]{DBHelper.class},
                new DBHandler(this));
    }

	private class DBHandler implements InvocationHandler {
        private DBHelper db;
        public DBHandler(DBHelper db) {
            this.db = db;
        }

        @Override
        public Object invoke(Object o, Method method, Object[] objects) throws Throwable {
            if (db != null){
                Log.d(TAG,"操作数据库前------");
                save();
                Log.d(TAG,"备份成功------");
                return method.invoke(db,objects);
            }
            return null;
        }
    }