1.責(zé)任鏈模式的定義及使用場景
定義：
責(zé)任鏈模式是行為型設(shè)計模式之一迄薄。使多個對象都有機會處理請求在跳，從而避免了請求的發(fā)送者和接受者之間的耦合關(guān)系岁忘。將這些對象連成一條鏈舵稠，并沿著這條鏈傳遞該請求蠢壹，直到有對象處理它為止
使用場景：
使多個對象都有機會處理請求嗓违，從而避免了請求的發(fā)送者和接收者之間的耦合關(guān)系。將這些對象連成一條鏈图贸，并沿著這條鏈傳遞該請求蹂季，只到有對象處理它為止

Paste_Image.png

public abstract class AbstractRequest {
    private Object obj;//處理對象
    public AbstractRequest(Object object) {
        this.obj = object;
    }
    public Object getContent() {
        return obj;
    }
    //獲取請求的級別
    public abstract int getRequestLevel();
}```

public abstract class AbstractHandler {
protected AbstractHandler nexthandler;//下一節(jié)點處理對象
public final void handleRequest(AbstractRequest request) {
if(getHandleLevel()==request.getRequestLevel()){
handle(request);
}else{
if(nexthandler!=null){
nexthandler.handleRequest(request);
}else{
System.out.println("All of handler can not handle the request");
}
}
}
//獲取處理者對象的處理級別
protected abstract int getHandleLevel();
//每個處理者對象的具體處理方式
protected abstract void handle(AbstractRequest request);
}```

public class Handler1 extends AbstractHandler {
    @Override
    protected int getHandleLevel() {
        return 1;
    }
    @Override
    protected void handle(AbstractRequest request) {
        System.out.println("Handler1 handle request:"+request.getRequestLevel());
    }
}```

public class Handler2 extends AbstractHandler {
@Override
protected int getHandleLevel() {
return 2;
}
@Override
protected void handle(AbstractRequest request) {
System.out.println("Handler2 handle request:"+request.getRequestLevel());
}
}```

public class Handler3 extends AbstractHandler {
    @Override
    protected int getHandleLevel() {
        return 3;
    }
    @Override
    protected void handle(AbstractRequest request) {
        System.out.println("Handler3 handle request:"+request.getRequestLevel());
    }
}```

public class Request1 extends AbstractRequest {
public Request1(Object object) {
super(object);
}
@Override
public int getRequestLevel() {
return 1;
}
}```

public class Request2 extends  AbstractRequest {
    public Request2(Object object) {
        super(object);
    }
    @Override
    public int getRequestLevel() {
        return 2;
    }
}```

public class Request3 extends AbstractRequest {
public Request3(Object object) {
super(object);
}
@Override
public int getRequestLevel() {
return 3;
}
}```

public class Request4 extends  AbstractRequest {
    public Request4(Object object) {
        super(object);
    }
    @Override
    public int getRequestLevel() {
        return 4;
    }
}```

public class Test {
public static void main(String args[]) {
AbstractHandler h1=new Handler1();
AbstractHandler h2=new Handler2();
AbstractHandler h3=new Handler3();
h1.nexthandler=h2;
h2.nexthandler=h3;
AbstractRequest r1=new Request1(h1);
AbstractRequest r2=new Request2(h2);
AbstractRequest r3=new Request3(h3);
AbstractRequest r4=new Request4(h3);
//總是從鏈?zhǔn)降氖锥税l(fā)起請求
h1.handleRequest(r1);
h1.handleRequest(r2);
h1.handleRequest(r3);
h1.handleRequest(r4);
}
}```
5. 責(zé)任鏈模式在Android中的實際應(yīng)用

責(zé)任鏈模式在Android源碼中比較類似的實現(xiàn)就是對于觸摸事件的分發(fā)處理跪者。每當(dāng)用戶接觸屏幕時棵帽，Android都會將對應(yīng)的事件包裝成一個事件對象從ViewTree的頂部至上而下地分發(fā)傳遞熄求。ViewGroup事件投遞的遞歸調(diào)用就類似于一條責(zé)任鏈渣玲，一旦尋找到責(zé)任者，那么將由責(zé)任者持有并消費掉該次事件弟晚，具體地體現(xiàn)在View的onTouchEvent方法中返回值的設(shè)置忘衍，如果onTouchEvent返回false，那么意味著當(dāng)前View不會是該次事件的復(fù)制人卿城，將不會對其持有枚钓；如果為true則相反，此時View會持有該事件并不再向外傳遞瑟押。
View的事件分發(fā)機制（MontionEvent的分發(fā)過程）：
public boolean dispatchTouchEvent（MotionEvent ev）
如果事件能夠傳遞到當(dāng)前的View搀捷，那么此方法一定會被調(diào)用。
public boolean onInterceptTouchEvent（MotionEvent ev）
用來判斷是否攔截某個事件
public boolean onTouchEvent(MotionEvent ev)
用來處理點擊事件
流轉(zhuǎn)關(guān)系（偽代碼）

public boolean dispatchTouchEvent(MotionEvent ev){
     boolean consume=false;
     if(onInterceptTouchEvent(ev)){
          consume=onTouchEvent(ev);
     }else{
          consume=child.dispatchTouchEvent(ev);
     }
     return consume;
     }```
出處：http://huangjunbin.com/page/2/