Redux is a predictable state container for JavaScript apps Redux是 JavaScript 状态容器，提供可预测化的状态管理。

Redux 文档开头就总结了Redux的意义。当然也非常详细的解释了Redux的三大原则和各模块作用，想入门请看Redux中文文档。

当你已经理清楚了Action，Reducer，Store直接的关系之后，你会有这样的疑问，Action怎么传递到Reducer中的？Reducer生成的新state又是怎么触发对应页面的刷新的？这个问题我也不想讲，因为这篇文章写的非常好-深入到源码：解读 redux 的设计思路与用法,我其实想从Android开发者的角度谈一谈直接对Redux思想的理解和Redux for Android的尝试。

Redux for Android的尝试

说干就干，这里模拟一个网络请求，先看效果。

再来看代码：

BaseReduxActivity 中使用Event来桥接View和state的改动，相当于 react-redux中的 connect

/**

*

* Created by mobilexu on 30/6/16.

*/

public abstract class BaseReduxActivity extends AppCompatActivity {

public EventBus eventBus;

@Override

protected void onCreate(@Nullable Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

eventBus = EventBus.getDefault();

eventBus.register(this);

}

@Override

protected void onDestroy() {

super.onDestroy();

eventBus.unregister(this);

}

/**

* 接收想要监听的状态变化

*

* @param state

*/

public void onEvent(State state) {

onStateChange(state);

}

protected abstract void onStateChange(State state);

}

Action中提供一个type，和一个string->Object的HashMap

/**

* Created by mobilexu on 2/7/16.

*/

public class Action {

private int type;

private HashMap hashMap;

public int getType() {

return type;

}

public Action(int type) {

this.type = type;

}

public Action(int type, HashMap hashMap) {

this.type = type;

this.hashMap = hashMap;

}

public HashMap appendHashParam(String key, Object object) {

if (hashMap == null) {

hashMap = new HashMap<>();

}

hashMap.put(key, object);

return hashMap;

}

public HashMap getHashMap() {

return hashMap;

}

}

ActionCreater简单的提供一下dispatch方法

/**

* Created by mobilexu on 3/7/16.

*/

public class ActionCreater {

public void dispatch(Action action) {

Store.getInstance().dispatch(action);

}

}

Reduce和State目前只是个接口

/**

* Created by mobilexu on 2/7/16.

*/

public interface Reduce {

State handleAction(Action action);

}

/**

* Created by mobilexu on 2/7/16.

*/

public interface State {

}

Store中提供了Reducer的注册和dispatch的真正实现，还有就是桥接了EventBus用于桥接view和state的改变

/**

* Created by mobilexu on 2/7/16.

*/

public class Store {

private static Store defaultInstance;

private EventBus eventBus;

private List reducers;

public static Store getInstance() {

if (defaultInstance == null) {

synchronized (EventBus.class) {

if (defaultInstance == null) {

defaultInstance = new Store();

}

}

}

return defaultInstance;

}

private Store() {

eventBus = EventBus.getDefault();

reducers = new ArrayList<>();

}

/**

* 合并reduce

*

* @param reduceList

*/

public void combineReducers(Reduce... reduceList) {

for (Reduce reduce : reduceList) {

reducers.add(reduce);

}

}

/**

* 添加单个reduce

*

* @param reduce

*/

public void addReduce(Reduce reduce) {

reducers.add(reduce);

}

/**

* 移除单个Reduce

*

* @param reduce

*/

public void removeReduce(Reduce reduce) {

reducers.remove(reduce);

}

/**

* 清空reducers

*/

public void clearAllReduce() {

reducers.clear();

}

/**

* 发送一个Action

*

* @param action

*/

public void dispatch(Action action) {

for (Reduce reduce : reducers) {

State localState = reduce.handleAction(action);

if (localState != null) {

eventBus.post(localState);

}

}

}

}

最后看一下如何使用

Reducer可以在Application中统一添加，也可以在各种的页面添加。

public class SecondActivity extends BaseReduxActivity {

private TextView ButtonTwo;

private SecondReduce reduce;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_second);

ButtonTwo = (TextView) findViewById(R.id.buttonTwo);

init();

render(null);

}

private void init() {

reduce = new SecondReduce();

Store.getInstance().addReduce(reduce);

ButtonTwo.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

new SecondActionCreater().changeText();

}

});

}

private void render(SecondState state) {

if (state == null)

return;

if (state.isLoading()) {

ButtonTwo.setText("。。。");

} else {

ButtonTwo.setText(state.getText());

}

}

@Override

protected void onStateChange(State state) {

if (state instanceof SecondState) {

render((SecondState) state);

}

}

@Override

protected void onDestroy() {

super.onDestroy();

Store.getInstance().removeReduce(reduce);

}

}

SecondActionCreater模拟了一次类似网络请求的操作,发送了俩个Action出去

public class SecondActionCreater extends ActionCreater {

public void changeText() {

dispatch(new Action(SecondReduce.ACTION_SECOND_SHOWLOADING));

new Handler().postDelayed(new Runnable() {

@Override

public void run() {

showText();

}

}, 3000);

}

private void showText() {

Action action = new Action(SecondReduce.ACTION_SECOND_SHOWTEXT);

action.appendHashParam("text", new Random().nextInt(10) + "文本");

dispatch(action);

}

}

SecondReduce 收到Action之后，根据type对数据进行加工

public class SecondReduce implements Reduce {

public static final int ACTION_SECOND_SHOWLOADING = 3;

public static final int ACTION_SECOND_SHOWTEXT = 4;

@Override

public State handleAction(Action action) {

switch (action.getType()) {

case ACTION_SECOND_SHOWLOADING:

return new SecondState(true, null);

case ACTION_SECOND_SHOWTEXT:

return new SecondState(false, action.getHashMap().get("text").toString());

default:

return null;

}

}

}

SecondState 简直就是个ViewModle

public class SecondState implements State {

private boolean isLoading;

private String text;

public SecondState(boolean isLoading, String text) {

this.isLoading = isLoading;

this.text = text;

}

public boolean isLoading() {

return isLoading;

}

public void setLoading(boolean loading) {

isLoading = loading;

}

public String getText() {

return text;

}

public void setText(String text) {

this.text = text;

}

}

整个过程，将操作都放在了SecondActionCreater 中，其实这个时候，ActionCreater就是MVP中的presenter，而Reducer就是生成ViewModle的过滤器，他不负责原始数据的采集，只是根据Action的描述，对数据进行一次加工,最后Reducer产生了一个State，通过EventBus维护的state和activity关系，进行了分发。

机智的读者会发现，redux 建议只维护一个全局 state ，而上面的框架中state是分散的，这里我有这样的考虑，原始app和web开发不太相同，一个工具app，从打开使用到最后关闭，可能会遍历几十个页面，这个时候如果维护全局一个state,那么势必会有不要的性能开销，而且这里我也可以通过监听不同的state来实现特殊情况下的需求。

@Override

protected void onStateChange(State state) {

if (state instanceof ChangeTextState) {

render((ChangeTextState) state);

} else if (state instanceof SecondState) {

renderSecond((SecondState) state);

}

}

上面简单写了一个redux for Android的框架，源码可以这里看到，下面的愿景是将DataBinding结合，那个时候，ActionCreater相当于Presenter,state相当于ViewModel,那这个架构就叫PVVM。

猝不及防的吹了个牛逼，不要见怪。不过还是欢迎大家提pr。