Android观察者模式简单实现

7观察者模式就是：当一个对象的状态发送改变时，所有依赖于它的对象都能得到通知并被自动更新。

下面介绍一种简单的使用方法，（下面有demo链接）先看一下project的目录构成：

ObserverListener是观察者接口，SubjectListener是被观察者接口，ObserverManager是观察者的管理类。

/**
 * Created by Administrator on 2017/9/28.
 * 观察者接口
 */

public interface ObserverListener {
    void observerUpData(String content);//刷新操作
}

/**
 * Created by Administrator on 2017/9/28.
 * 被观察者接口
 */

public interface SubjectListener {
    void add(ObserverListener observerListener);
    void notifyObserver(String content);
    void remove(ObserverListener observerListener);
}

下面是比较重要的管理类：

public class ObserverManager implements SubjectListener {
    private static ObserverManager observerManager;
    //观察者接口集合
    private List<ObserverListener> list = new ArrayList<>();

    /**
     * 单例
     */
    public static ObserverManager getInstance(){
        if (null == observerManager){
            synchronized (ObserverManager.class){
                if (null == observerManager){
                    observerManager = new ObserverManager();
                }
            }
        }
        return observerManager;
    }

    /**
     * 加入监听队列
     */
    @Override
    public void add(ObserverListener observerListener) {
        list.add(observerListener);
    }

    /**
     * 通知观察者刷新数据
     */
    @Override
    public void notifyObserver(String content) {
        for (ObserverListener observerListener : list){
            observerListener.observerUpData(content);
        }
    }

    /**
     * 监听队列中移除
     */
    @Override
    public void remove(ObserverListener observerListener) {
        if (list.contains(observerListener)){
            list.remove(observerListener);
        }
    }
}

效果是当点击ThirdActivity中的按钮时，执行ObserverManager.getInstance().notifyObserver(“观察者请刷新信息”);

然后所有添加到监听队列的Activity都会更新数据，ObserverManager.getInstance().add(this)就是添加到监听队列的方法，更新操作执行在observerUpData(String content)方法中。

下面是3个Activity，很简单：

public class MainActivity extends AppCompatActivity implements ObserverListener {
    private TextView textView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView = (TextView) findViewById(R.id.tv);
        findViewById(R.id.btn).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //ObserverManager.getInstance().notifyObserver("观察者请刷新信息");
                Intent intent = new Intent(MainActivity.this,SecondActivity.class);
                startActivity(intent);
            }
        });

        //注册
        ObserverManager.getInstance().add(this);

    }

    @Override
    public void observerUpData(String content) {
        Log.d("vvvvvvvvvvvvvvv","11111111111");
        textView.setText(content);
    }
}

public class SecondActivity extends AppCompatActivity implements ObserverListener {
    private TextView textView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        textView = (TextView) findViewById(R.id.tv2);
        findViewById(R.id.btn2).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(SecondActivity.this,ThirdActivity.class);
                startActivity(intent);
            }
        });

        //注册
        ObserverManager.getInstance().add(this);
    }

    @Override
    public void observerUpData(String content) {
        Log.d("vvvvvvvvvvvvvvv","2222222222");
        textView.setText(content);
    }
}

public class ThirdActivity extends AppCompatActivity implements ObserverListener {
    private TextView textView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_third);
        textView = (TextView) findViewById(R.id.tv3);
        findViewById(R.id.btn3).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                ObserverManager.getInstance().notifyObserver("观察者请刷新信息");
            }
        });

        //注册
        ObserverManager.getInstance().add(this);
    }

    @Override
    public void observerUpData(String content) {
        Log.d("vvvvvvvvvvvvvvv","33333333333");
        textView.setText(content);
    }
}

布局都是一个TextView和一个Button。

代码下载地址：http://download.youkuaiyun.com/download/gsg8709/10003238