Android——观察者模式的使用

观察者模式的使用

大致需要四步：

1.提供观察者接口，用来更新update数据

/**观察者接口，给那些观察者数据变化发生时候的更新
* Created by PeLon on 2017/7/28.
*/

public interface Observer {
public void update(Subject subject);
}

2.创建具体的观察者，实现该接口，具体实现接口的更新方法

（可以设置观察者名字，根据目标对象提醒要做的事情）

public class ConcreObserver implements Observer {
//观察者名字
private String name;

private Context context;

//获取目标类的状态同步到观察者的状态中
private String WeatherContent;

//提醒要做的事情

private String remindThing;

public ConcreObserver(Context context) {
this.context=context;
}

public ConcreObserver(String name, String weatherContent, String remindThing) {
this.name = name;
WeatherContent = weatherContent;
this.remindThing = remindThing;
}

@Override
public void update(Subject subject) {
WeatherContent=((ConcreSubject)subject).getWeatherContent();
String str=name+"收到了天气情况："+WeatherContent+"准备"+remindThing+"\n";
Intent intent=new Intent();
intent.setAction("a");
intent.putExtra("response",str);
context.sendBroadcast(intent);
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public String getWeatherContent() {
return WeatherContent;
}

public void setWeatherContent(String weatherContent) {
WeatherContent = weatherContent;
}

public String getRemindThing() {
return remindThing;
}

public void setRemindThing(String remindThing) {
this.remindThing = remindThing;
}
}

3.创建目标对象（被观察的）subject，添加加入、删除、提醒所有观察者的方法

/**目标对象，将观察者放入集合内，并添加加入、删除的借口
* Created by PeLon on 2017/7/28.
*/

public class Subject {
private List<Observer> list=new ArrayList<>();

public void attach(Observer observer)
{
list.add(observer);

}
public void deleteObserver(Observer observer)
{
list.remove(observer);

}

public  void notifyObservers()
{
for (Observer observer:list)
{
observer.update(this);
}
}

}

4.创建具体目标对象，继承subject，获得具体目标对象内容（天气），并且在设置的时候

this.notify通知所有观察者。

public class ConcreSubject extends Subject {

//获得具体目标对象内容，并且在设置的时候通知观察者
//获得的天气情况
private String WeatherContent;

public ConcreSubject() {
}

public void setConcerSubjectState(String WeatherContent) {
this.WeatherContent = WeatherContent;
this.notifyObservers();
}

public String getWeatherContent() {
return WeatherContent;
}
}

在activity中调用

public class MainActivity extends AppCompatActivity {
private ConcreObserver observer,observer2;
private EditText text;
private TextView textView;
private Button button;
private StringBuffer buffer=new StringBuffer();
private BroadcastReceiver receiver=new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
String string=intent.getStringExtra("response");
Toast.makeText(MainActivity.this, string,Toast.LENGTH_SHORT).show();
buffer.append(string);
textView.setText(buffer.toString());
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

text= (EditText) findViewById(R.id.edittext);
button= (Button) findViewById(R.id.send);
textView= (TextView) findViewById(R.id.textview);

IntentFilter filter=new IntentFilter();
filter.addAction("a");
registerReceiver(receiver,filter);

//1.创建目标对象
final ConcreSubject weather=new ConcreSubject();

//2.创建观察者
observer=new ConcreObserver(this);
observer.setName("妈妈：");
observer.setRemindThing("适合购物");

observer2=new ConcreObserver(this);
observer2.setName("女朋友：");
observer2.setRemindThing("适合约会");

//3.注册观察者
weather.attach(observer);
weather.attach(observer2);

//4.发送目标

button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String weathercontent=text.getText().toString().trim();
weather.setConcerSubjectState(weathercontent);

}
});

同样是一个天气情况，观察天气情况两个观察者做出不一样的选择，这便是观察者模式的一种体现。