Android培訓(xùn)實(shí)戰(zhàn)教程之事件傳遞

Touch事件傳遞和攔截機(jī)制

關(guān)于touch事件的主要方法介紹
1. ViewGroup的子類（容器類，如：LinearLayout，RelativeLayout等）
    1. dispatchTouchEvent(MotionEvent ev)  事件的分發(fā)
    2. onInterceptTouchEvent(MotionEvent ev)  事件的攔截
    3. onTouchEvent(MotionEvent ev)  事件的處理
2. View的子類（非容器類，如：TextView，ImageView等）
    1. dispatchTouchEvent(MotionEvent ev)  事件的分發(fā)
    2. onTouchEvent(MotionEvent ev)  事件的處理

 區(qū)別：
    非容器類沒(méi)有onInterceptTouchEvent(MotionEvent ev)  事件的攔截



下面是測(cè)試案例的主要代碼

1. 打印日志的類

        public class LogUtils {
            public static void printLog(String tag,MotionEvent ev,String touchName) {
                switch (ev.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    //按下
                    Log.i(tag, touchName + "按下");
                    break;
                case MotionEvent.ACTION_MOVE:
                    //按下
                    Log.d(tag, touchName + "移動(dòng)");
                    break;
                case MotionEvent.ACTION_UP:
                    //按下
                    Log.e(tag, touchName + "松開(kāi)");
                    break;
        
                default:
                    break;
                }
            }
        }

2. 第一個(gè)容器類（為了方便布局，本案例中用FrameLayout做基類，在事件攔截機(jī)制中和直接繼承ViewGroup類一致，因?yàn)镕rameLayout沒(méi)有覆蓋ViewGroup的上面三個(gè)touch方法）
        
        public class ViewGroupOne extends FrameLayout {
        
            public ViewGroupOne(Context context, AttributeSet attrs) {
                super(context, attrs);
                // TODO Auto-generated constructor stub
            }
        
            public ViewGroupOne(Context context) {
                super(context);
                // TODO Auto-generated constructor stub
            }
            
            //分發(fā)事件
            @Override
            public boolean dispatchTouchEvent(MotionEvent ev) {
                // TODO Auto-generated method stub
                LogUtils.printLog("ViewGroupOne",ev, "dispatchTouchEvent");
                  
                return super.dispatchTouchEvent(ev);
            }
            
            //攔截事件
            @Override
            public boolean onInterceptTouchEvent(MotionEvent ev) {
                // TODO Auto-generated method stub
                LogUtils.printLog("ViewGroupOne",ev, "onInterceptTouchEvent");
                return super.onInterceptTouchEvent(ev);
            }
            
            //處理事件
            @Override
            public boolean onTouchEvent(MotionEvent ev) {
                // TODO Auto-generated method stub
                LogUtils.printLog("ViewGroupOne",ev, "onTouchEvent");
                return super.onTouchEvent(ev);
            }
        
        }

3. 第二個(gè)容器類
            
        public class ViewGroupTwo extends FrameLayout {
        
            public ViewGroupTwo(Context context, AttributeSet attrs) {
                super(context, attrs);
                // TODO Auto-generated constructor stub
            }
        
            public ViewGroupTwo(Context context) {
                super(context);
                // TODO Auto-generated constructor stub
            }
            
            //分發(fā)事件
            @Override
            public boolean dispatchTouchEvent(MotionEvent ev) {
                // TODO Auto-generated method stub
                LogUtils.printLog("ViewGroupTwo",ev, "dispatchTouchEvent");
                return super.dispatchTouchEvent(ev);
            }
            
            //攔截事件
            @Override
            public boolean onInterceptTouchEvent(MotionEvent ev) {
                // TODO Auto-generated method stub
                LogUtils.printLog("ViewGroupTwo",ev, "onInterceptTouchEvent");
                return super.onInterceptTouchEvent(ev);
            }
            
            //處理事件
            @Override
            public boolean onTouchEvent(MotionEvent event) {
                // TODO Auto-generated method stub
                LogUtils.printLog("ViewGroupTwo",event, "onTouchEvent");
                return super.onTouchEvent(event);
            }
        
        }

4. 非容器類

        public class MyView extends View {
        
            public MyView(Context context, AttributeSet attrs) {
                super(context, attrs);
                // TODO Auto-generated constructor stub
            }
        
            public MyView(Context context) {
                super(context);
                // TODO Auto-generated constructor stub
            }
        
            // 分發(fā)事件
            @Override
            public boolean dispatchTouchEvent(MotionEvent ev) {
                // TODO Auto-generated method stub
                LogUtils.printLog("MyView",ev, "dispatchTouchEvent");
                return super.dispatchTouchEvent(ev);
            }
        
            // 處理事件
            @Override
            public boolean onTouchEvent(MotionEvent event) {
                // TODO Auto-generated method stub
                LogUtils.printLog("MyView",event, "onTouchEvent");
                return super.onTouchEvent(event);
            }
        
        }

5. 主界面的布局

        <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
            xmlns:tools="http://schemas.android.com/tools"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:paddingBottom="@dimen/activity_vertical_margin"
            android:paddingLeft="@dimen/activity_horizontal_margin"
            android:paddingRight="@dimen/activity_horizontal_margin"
            android:paddingTop="@dimen/activity_vertical_margin"
            tools:context=".MainActivity" >
        
            <com.itheima13.eventdemo.ViewGroupOne
                android:layout_width="200dip"
                android:layout_height="200dip"
                android:background="#ff0000" >
        
                <com.itheima13.eventdemo.ViewGroupTwo
                    android:layout_width="150dip"
                    android:layout_height="150dip"
                    android:background="#00ff00" >
        
                    <com.itheima13.eventdemo.MyView
                        android:layout_width="100dip"
                        android:layout_height="100dip"
                        android:background="#0000ff" />
                </com.itheima13.eventdemo.ViewGroupTwo>
            </com.itheima13.eventdemo.ViewGroupOne>
        
        </RelativeLayout>

    預(yù)覽結(jié)果如下圖(紅色是ViewGroupOne，綠色是ViewGroupTwo，藍(lán)色是MyView)：



上面原始代碼都是默認(rèn)的情況，運(yùn)行后點(diǎn)擊藍(lán)色區(qū)域（按下，移動(dòng)，松開(kāi)）結(jié)果如圖：
總結(jié): 默認(rèn)情況只相應(yīng)touch事件的down狀態(tài)，而且事件默認(rèn)傳遞到最內(nèi)層的子控件(MyView)onTouchEvent方法，由于默認(rèn)MyView的onTouchEvent的方法沒(méi)有處理，所以事件依次回傳至父控件（ViewGroupTwo,ViewGroupOne）的onTouchEvent方法，由于每層都沒(méi)處理，所以事件回傳至最外層父控件后消失


由于情況復(fù)雜，下面以三個(gè)方法為核心介紹所有情況。（一個(gè)案例測(cè)試一種情況，每個(gè)案例的代碼改變都是在上面的基礎(chǔ)代碼上修改測(cè)試，也就是每個(gè)案例每種情況的代碼都是獨(dú)立的，只需參考上面的基本代碼和案例中每種情況修改的代碼即可。）

dispatchTouchEvent(MotionEvent ev)方法

* 有三種情況
    * 直接返回true 
        * 只修改ViewGroupTwo的dispatchTouchEvent方法測(cè)試
        
                //分發(fā)事件
                @Override
                public boolean dispatchTouchEvent(MotionEvent ev) {
                    // TODO Auto-generated method stub
                    LogUtils.printLog("ViewGroupTwo",ev, "dispatchTouchEvent");
                    return true;
                }

         運(yùn)行后對(duì)藍(lán)色區(qū)域做了按下，移動(dòng)，松開(kāi)的操作，運(yùn)行結(jié)果如下圖：         * 只修改MyView的dispatchTouchEvent方法測(cè)試
        
                @Override
                public boolean dispatchTouchEvent(MotionEvent ev) {
                    // TODO Auto-generated method stub
                    LogUtils.printLog("MyView",ev, "dispatchTouchEvent");
                    return true;//super.dispatchTouchEvent(ev);
                }

        運(yùn)行后對(duì)藍(lán)色區(qū)域做了按下，移動(dòng)，松開(kāi)的操作，運(yùn)行結(jié)果如下圖：         
        結(jié)果分析：
        事件傳遞至子控件的dispatchTouchEvent終止。事件只有按順序傳遞，沒(méi)有回傳情況。并且事件的三種情況(down,move,up)都有處理回調(diào)
    
    * 直接返回false
        * 只修改ViewGroupTwo的dispatchTouchEvent方法測(cè)試
                
                @Override
                public boolean dispatchTouchEvent(MotionEvent ev) {
                    // TODO Auto-generated method stub
                    LogUtils.printLog("ViewGroupTwo",ev, "dispatchTouchEvent");
                    return false;//super.dispatchTouchEvent(ev);
                }

        運(yùn)行后對(duì)藍(lán)色區(qū)域做了按下，移動(dòng)，松開(kāi)的操作，運(yùn)行結(jié)果如下圖：         
        * 只修改MyView的dispatchTouchEvent方法測(cè)試
        
                // 分發(fā)事件
                @Override
                public boolean dispatchTouchEvent(MotionEvent ev) {
                    // TODO Auto-generated method stub
                    LogUtils.printLog("MyView",ev, "dispatchTouchEvent");
                    return false;//super.dispatchTouchEvent(ev);
                }

        運(yùn)行后對(duì)藍(lán)色區(qū)域做了按下，移動(dòng)，松開(kāi)的操作，運(yùn)行結(jié)果如下圖：         
     結(jié)果分析：
     事件傳遞至當(dāng)前控件的dispatchTouchEvent終止，并且事件回傳給父控件的onTouchEvent方法，此過(guò)程中只相應(yīng)事件的down狀態(tài)

    * 直接調(diào)用super.dispatchTouchEvent(ev);

    結(jié)果分析：默認(rèn)情況,直接調(diào)用ViewGroup的dispatchTouchEvent(ev)方法，事件會(huì)傳遞給當(dāng)前的控件的onInterceptTouchEvent(MotionEvent ev)方法。

onInterceptTouchEvent(MotionEvent ev) 方法
* 有三種情況
    * 直接返回true
        * 只修改ViewGroupTwo的onInterceptTouchEvent方法
        
                //攔截事件
                @Override
                public boolean onInterceptTouchEvent(MotionEvent ev) {
                    // TODO Auto-generated method stub
                    LogUtils.printLog("ViewGroupTwo",ev, "onInterceptTouchEvent");
                    return true;//super.onInterceptTouchEvent(ev);
                }

        運(yùn)行后對(duì)藍(lán)色區(qū)域做了按下，移動(dòng)，松開(kāi)的操作，運(yùn)行結(jié)果如下圖：
    結(jié)果分析：touch事件被當(dāng)前控件攔截，不傳遞給子控件，并調(diào)用自己的onTouchEvent方法處理事件
    * 直接返回false
        * 只修改ViewGroupTwo的onInterceptTouchEvent方法
        
                //攔截事件
                @Override
                public boolean onInterceptTouchEvent(MotionEvent ev) {
                    // TODO Auto-generated method stub
                    LogUtils.printLog("ViewGroupTwo",ev, "onInterceptTouchEvent");
                    return false;//super.onInterceptTouchEvent(ev);
                }

        運(yùn)行后對(duì)藍(lán)色區(qū)域做了按下，移動(dòng)，松開(kāi)的操作，運(yùn)行結(jié)果如下圖：
   結(jié)果分析：touch事件傳遞給子控件，由子控件處理事件

    * 直接調(diào)用super.onInterceptTouchEvent(ev) (調(diào)用ViewGroup的方法)
    

        運(yùn)行后對(duì)藍(lán)色區(qū)域做了按下，移動(dòng)，松開(kāi)的操作，運(yùn)行結(jié)果如下圖：     結(jié)果分析：touch事件傳遞給子控件，由子控件處理事件（與直接返回false類似）    

 onTouchEvent(MotionEvent ev) 方法
* 有三種情況
    * 直接返回true
        * 只修改ViewGroupTwo的onTouchEvent方法
            
                //處理事件
                @Override
                public boolean onTouchEvent(MotionEvent event) {
                    // TODO Auto-generated method stub
                    LogUtils.printLog("ViewGroupTwo",event, "onTouchEvent");
                    return true;//super.onTouchEvent(event);
                }

            運(yùn)行后對(duì)藍(lán)色區(qū)域做了按下，移動(dòng)，松開(kāi)的操作，運(yùn)行結(jié)果如下圖：
    結(jié)果分析：down狀態(tài)：當(dāng)touch事件回傳給當(dāng)前控件的時(shí)候，由于返回ture，所有事件回傳終止。針對(duì)move和up狀態(tài)：事件到當(dāng)前的onTouchEvent方法終止。也就是說(shuō)子控件無(wú)法響應(yīng)事件。
    
    * 直接返回false
        * 只修改ViewGroupTwo的onTouchEvent方法
            
                //處理事件
                @Override
                public boolean onTouchEvent(MotionEvent event) {
                    // TODO Auto-generated method stub
                    LogUtils.printLog("ViewGroupTwo",event, "onTouchEvent");
                    return false;//super.onTouchEvent(event);
                }

            運(yùn)行后對(duì)藍(lán)色區(qū)域做了按下，移動(dòng)，松開(kāi)的操作，運(yùn)行結(jié)果如下圖：
    >結(jié)果分析：事件回傳給父控件
    
    * 直接調(diào)用super.onTouchEvent(ev)
        * 只修改ViewGroupTwo的onTouchEvent方法
            
                //處理事件
                @Override
                public boolean onTouchEvent(MotionEvent event) {
                    // TODO Auto-generated method stub
                    LogUtils.printLog("ViewGroupTwo",event, "onTouchEvent");
                    return super.onTouchEvent(event);
                }

            運(yùn)行后對(duì)藍(lán)色區(qū)域做了按下，移動(dòng)，松開(kāi)的操作，運(yùn)行結(jié)果如下圖：
    >結(jié)果分析：事件回傳給父控件

事件反向攔截

主要是反向攔截父控件的onInterceptTouchEvent

* 沒(méi)申請(qǐng)反向攔截父控件onInterceptTouchEvent的方法

    1. 只在ViewGroupTwo中覆蓋了onTouchEvent方法，并且事件消費(fèi)
        
            //處理事件
            @Override
            public boolean onTouchEvent(MotionEvent event) {
                // TODO Auto-generated method stub
                LogUtils.printLog("ViewGroupTwo",event, "onTouchEvent");
                return true;//super.onTouchEvent(event);
            }

    運(yùn)行后對(duì)藍(lán)色區(qū)域做了按下，移動(dòng)，松開(kāi)的操作，運(yùn)行結(jié)果如下圖：
* 申請(qǐng)反向攔截父控件的onInterceptTouchEvent的方法
    1. 在上面的代碼基礎(chǔ)上，添加dispatchTouchEvent方法的覆蓋
    
            @Override
            public boolean dispatchTouchEvent(MotionEvent ev) {
                // TODO Auto-generated method stub
                requestDisallowInterceptTouchEvent(true);
                LogUtils.printLog("ViewGroupTwo",ev, "dispatchTouchEvent");
                return super.dispatchTouchEvent(ev);
            }
    注意多了requestDisallowInterceptTouchEvent(true);方法調(diào)用，該方法是攔截父控件的onInterceptTouchEvent方法的執(zhí)行（針對(duì)move，up狀態(tài)）

    運(yùn)行后對(duì)藍(lán)色區(qū)域做了按下，移動(dòng)，松開(kāi)的操作，運(yùn)行結(jié)果如下圖：

    >結(jié)果分析： 申請(qǐng)反向攔截后，父控件的onInterceptTouchEvent方法將不再執(zhí)行，案例如：智慧北京項(xiàng)目的輪播圖事件反攔截

    >源碼解釋：
        requestDisallowInterceptTouchEvent(true); 方法源碼如：

        public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
        
                if (disallowIntercept == ((mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0)) {
                    // We're already in this state, assume our ancestors are too
                    return;
                }
        
                if (disallowIntercept) {
                    //主要是記錄攔截的標(biāo)記 看dispatchTouchEvent方法的代碼片段
                    mGroupFlags |= FLAG_DISALLOW_INTERCEPT;
                } else {
                    mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
                }
        
                // Pass it up to our parent
                if (mParent != null) {
                    //繼續(xù)設(shè)置父控件的攔截模式
                    mParent.requestDisallowInterceptTouchEvent(disallowIntercept);
                }
            }

         dispatchTouchEvent方法代碼片段：
            對(duì)上面設(shè)置的狀態(tài)值mGroupFlags判斷
            final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
            if (!disallowIntercept) {//根據(jù)狀態(tài)值是否調(diào)用onInterceptTouchEvent
                intercepted = onInterceptTouchEvent(ev);
                ev.setAction(action); // restore action in case it was changed
            } else {
                intercepted = false;
            }
        要點(diǎn)解析：
            看運(yùn)行效果圖可知，down事件執(zhí)行的時(shí)候，已經(jīng)設(shè)置了反向攔截的狀態(tài)，所有到move，up狀態(tài)執(zhí)行的時(shí)候，判斷就起到了攔截的效果

#### 事件傳遞和攔截流程圖(針對(duì)down事件的流程)


 實(shí)際操作會(huì)以下2點(diǎn)就可以了

1. 只需要做自己onTouchEvent方法的事件處理，并且返回值設(shè)置為true就可以滿足自己事件處理
2. 申請(qǐng)不讓父控件的onInterceptTouchEvent的方法執(zhí)行


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