前言
观察者模式定义了对象之间的一对多依赖,让多个观察者对象同时监听一个主题对象,当主题对象发生变化时,它的所有观察者都会收到通知并作出相应的动作。
观察者模式又叫发布订阅模式,需要观察者对被观察者发布的的动作进行订阅。
实现
主要类
我们新建的这几个类中,Event是事件类,用于包装触发事件的相关信息;MouseEventType接口中定义了各种事件类型;EventLisenter是监听器类,它是观察者的桥梁;Mouse是被观察者类,当它作出动作时,观察者就会反应并作出相应动作。MouseEventCallback是观察者类
接下来我们就来实现一下
创建Event和MouseEventType
Event:
public class Event {
private Object source;//事件源,事件发起者
private Object target;//事件触发,要通知谁
private Method callback;//事件触发,要做什么动作,回调
private String trigger;//事件名称,触发的是什么事件
private long time;//
public Event(Object target,Method callback) {
this.target = target;
this.callback =callback;
}
public Event setSource(Object source) {
this.source = source;
return this;
}
public Event setTime(long time) {
this.time = time;
return this;
}
public Object getSource() {
return source;
}
public Event setTrigger(String trigger) {
this.trigger = trigger;
return this;
}
public long getTime() {
return time;
}
public Object getTarget() {
return target;
}
public Method getCallback() {
return callback;
}
@Override
public String toString() {
return "Event{" +
"source=" + source +
", target=" + target +
", callback=" + callback +
", trigger='" + trigger + '\'' +
", time=" + time +
'}';
}
}
MouseEventType:
public interface MouseEventType {
String ON_CLICK = "click";
String ON_DOUBLE_CLICK = "doubleClick";
String ON_UP = "up";
String ON_DOWN = "down";
String ON_MOVE = "move";
String ON_WHEEEL = "wheel";
String ON_OVER ="over";
String ON_BLUR = "blur";
String ON_FOCUS = "focus";
}
Event为事件类,里面属性包含source事件源、target事件通知目标、callback事件回调、trigger事件名称
MouseEventType用于定义各种事件名称;
创建监听器类EventLisenter
这个类时观察者的桥梁
EventLisenter :
public class EventLisenter {
protected Map<String,Event> events = new HashMap<String,Event>();
public void addLisenter(String eventType, Object target) {
try {
this.addLisenter(eventType,
target,
target.getClass().getMethod("on"+toUpperFirstCase(eventType),Event.class));
} catch (Exception e){
e.printStackTrace();
}
}
public void addLisenter(String eventType, Object target,Method callback) {
events.put(eventType,new Event(target,callback));
}
private void trigger(Event event) {
event.setSource(this);
event.setTime(System.currentTimeMillis());
try{
if(event.getCallback()!=null) {
event.getCallback().invoke(event.getTarget(),event);
}
} catch (Exception e){
e.printStackTrace();
}
}
protected void trigger(String trigger) {
if(!this.events.containsKey(trigger)) {
return;
}
trigger(this.events.get(trigger).setTrigger(trigger));
}
private String toUpperFirstCase(String str) {
char[] chars = str.toCharArray();
chars[0] -= 32;
return String.valueOf(chars);
}
这个类中,用于事件订阅,里面将相应的事件存放到Map中,然后trigger是用于触发,通过传递进来的事件名称触发相应的事件
创建被观察者
Mouse :
public class Mouse extends EventLisenter{
public void click() {
System.out.println("调用单击方法");
this.trigger(MouseEventType.ON_CLICK);
}
public void doubleClick() {
System.out.println("调用双击方法");
this.trigger(MouseEventType.ON_DOUBLE_CLICK);
}
public void up() {
System.out.println("调用弹起方法");
this.trigger(MouseEventType.ON_UP);
}
public void down() {
System.out.println("调用按下方法");
this.trigger(MouseEventType.ON_DOWN);
}
public void move() {
System.out.println("调用移动方法");
this.trigger(MouseEventType.ON_MOVE);
}
public void wheel() {
System.out.println("调用滚动方法");
this.trigger(MouseEventType.ON_WHEEEL);
}
public void over(){
System.out.println("调用悬停方法");
this.trigger(MouseEventType.ON_OVER);
}
public void blur() {
System.out.println("调用获焦方法");
this.trigger(MouseEventType.ON_BLUR);
}
public void focus() {
System.out.println("调用失焦方法");
this.trigger(MouseEventType.ON_FOCUS);
}
}
这个类继承EventLisenter类,其相应的方法被调用会触发trigger方法
定义观察者类
MouseEventCallback
public class MouseEventCallback {
public void onClick(Event e) {
System.out.println("============触发鼠标点击事件============="+"\n"+e);
}
public void onDoubleClick(Event e) {
System.out.println("============触发鼠标双击事件============="+"\n"+e);
}
public void onUp(Event e) {
System.out.println("============触发鼠标弹起事件============="+"\n"+e);
}
public void onDown(Event e) {
System.out.println("============触发鼠标按下事件============="+"\n"+e);
}
public void onMove(Event e) {
System.out.println("============触发鼠标移动事件============="+"\n"+e);
}
public void onWheel(Event e) {
System.out.println("============触发鼠标滚动事件============="+"\n"+e);
}
public void onOver(Event e) {
System.out.println("============触发鼠标悬停事件============="+"\n"+e);
}
public void onBlur(Event e) {
System.out.println("============触发鼠标失焦事件============="+"\n"+e);
}
public void onFocus(Event e) {
System.out.println("============触发鼠标获焦事件============="+"\n"+e);
}
}
测试
Test
public class Test {
public static void main(String[] args) {
try{
MouseEventCallback callback = new MouseEventCallback();
Mouse mouse = new Mouse();
mouse.addLisenter(MouseEventType.ON_CLICK,callback);
mouse.click();
} catch (Exception e) {
e.printStackTrace();
}
}
}
测试中,我们可以看到,被观察者mouse 使用addLisenter添加了一个监听事件,当其触发对应的方方时,会引起观察者相应的动作
我们测试看看
总结来说,这个观察者模式中,被观察者有一个注册表,初始化时,我们进行订阅,将相应的事件存放到注册表中,一旦被观察者作出某个动作,就会从注册表中拿到相应的事件并执行