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136 lines
2.6 KiB
136 lines
2.6 KiB
---
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观察者模式
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---
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#### 目录
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1. 思维导图
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2. 概述
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3. 常见实现例子
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4. 具体实现
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5. 参考
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#### 思维导图
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#### 概述
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观察者模式定义了对象间一种一对多的依赖关系，使得每当一个对象改变状态，则所有依赖它的对象都会得到通知并自动更新。它的最重要作用就是解耦，将被观察者和观察者解耦，使得它们之间的依赖性更小。
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#### 常见实现例子
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1. 常见的发布订阅模式
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2. ListView 的 Adapter 的 notifyDataSetChanged
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3. BroadcastReceiver
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4. EventBus
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5. RxJava
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#### 具体实现
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首先定义一个观察者的接口：
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```java
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public interface Observer {
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void onUpdate();
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}
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```
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然后具体的观察者实现：
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```java
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public class Observer1 implements Observer {
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@Override
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public void onUpdate() {
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System.out.println("Observer1 收到通知！");
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}
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}
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```
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```java
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public class Observer2 implements Observer {
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@Override
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public void onUpdate() {
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System.out.println("Observer2 收到通知！");
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}
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}
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```
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在创建一个被观察者对象接口：
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```java
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public interface Subject {
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/**
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* 添加观察者
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*/
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void add(Observer observer);
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/**
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* 删除观察者
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*/
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void delete(Observer observer);
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/**
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* 通知所有观察者
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*/
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void notifyAllObservers();
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/**
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* 自身的操作
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*/
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void operation();
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}
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```
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抽象主题：
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```java
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public abstract class AbstractSubject implements Subject {
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private Vector<Observer> vector = new Vector<>();
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@Override
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public void add(Observer observer) {
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vector.add(observer);
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}
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@Override
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public void delete(Observer observer) {
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vector.remove(observer);
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}
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@Override
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public void notifyAllObservers() {
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Enumeration<Observer> enumeration = vector.elements();
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while (enumeration.hasMoreElements()) {
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enumeration.nextElement().onUpdate();
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}
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}
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}
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```
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具体的观察者对象：
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```java
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public class MySubject extends AbstractSubject {
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@Override
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public void operation() {
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System.out.println("执行更新！");
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notifyAllObservers();
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}
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}
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```
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测试：
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```java
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public class ObserverTest {
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public static void main(String[] args) {
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MySubject mySubject = new MySubject();
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mySubject.add(new Observer1());
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mySubject.add(new Observer2());
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mySubject.operation();
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}
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}
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```
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#### 参考
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[Observer（观察者模式）](https://github.com/jeanboydev/Android-ReadTheFuckingSourceCode/blob/master/article/design_patterns/%E8%AE%BE%E8%AE%A1%E6%A8%A1%E5%BC%8F-Observer.md) |