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【Android】为啥事件传递这么频繁却不会造成内存抖动

引言
测试
- 测试代码
- 测试一两次手指按下起来
- 测试二 - 不同的页面测试
- 测试三同一个应用杀进程测试
- 测试四不同进程
- 测试结果+总结
源码分析

引言

一般在Android开发中我们被要求说在onDraw方法不要新建对象，那为什么整体事件传递的时候，MotionEvent对象一直被回调，却没有造成内存波动，是为什么呢？

测试

针对这个问题，我专门做了测试，在dispatchTouchEvent方法中打印MotionEvent 对象的hashCode和信息。

测试代码

public class DiyView extends View{...@Overridepublic boolean dispatchTouchEvent(MotionEvent event) {Log.d("zhangyu20201217", "dispatchTouchEvent:" + System.identityHashCode(event) + " " + event.hashCode() + " " + event);return super.dispatchTouchEvent(event);}...

以下是测试结果：

测试一两次手指按下起来

2020-12-17 08:01:21.457 18401-18401/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:154259924 hashCode:154259924 MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=197.96436, y[0]=174.92969, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=39665544, downTime=39665544, deviceId=0, source=0x1002 }
2020-12-17 08:01:21.506 18401-18401/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:154259924 hashCode:154259924 MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=197.96436, y[0]=189.60889, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=4, eventTime=39665592, downTime=39665544, deviceId=0, source=0x1002 }
2020-12-17 08:01:21.531 18401-18401/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:154259924 hashCode:154259924 MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=194.96509, y[0]=199.68668, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=5, eventTime=39665614, downTime=39665544, deviceId=0, source=0x1002 }
2020-12-17 08:01:21.550 18401-18401/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:154259924 hashCode:154259924 MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=193.4578, y[0]=211.47052, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=4, eventTime=39665633, downTime=39665544, deviceId=0, source=0x1002 }
2020-12-17 08:01:21.569 18401-18401/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:154259924 hashCode:154259924 MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=188.96655, y[0]=223.7197, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=5, eventTime=39665651, downTime=39665544, deviceId=0, source=0x1002 }
2020-12-17 08:01:21.587 18401-18401/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:154259924 hashCode:154259924 MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=179.96875, y[0]=240.86429, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=7, eventTime=39665670, downTime=39665544, deviceId=0, source=0x1002 }
2020-12-17 08:01:21.604 18401-18401/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:154259924 hashCode:154259924 MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=171.245, y[0]=250.92578, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=5, eventTime=39665688, downTime=39665544, deviceId=0, source=0x1002 }
2020-12-17 08:01:21.622 18401-18401/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:154259924 hashCode:154259924 MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=165.96118, y[0]=260.61737, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=6, eventTime=39665707, downTime=39665544, deviceId=0, source=0x1002 }
2020-12-17 08:01:21.641 18401-18401/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:154259924 hashCode:154259924 MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=162.96191, y[0]=267.41992, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=3, eventTime=39665722, downTime=39665544, deviceId=0, source=0x1002 }
2020-12-17 08:01:21.689 18401-18401/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:154259924 hashCode:154259924 MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=162.96191, y[0]=268.97266, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=39665773, downTime=39665544, deviceId=0, source=0x1002 }
2020-12-17 08:01:21.690 18401-18401/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:154259924 hashCode:154259924 MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=162.96191, y[0]=268.97266, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=39665779, downTime=39665544, deviceId=0, source=0x1002 }

2020-12-17 08:06:32.075 18401-18401/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:154259924 hashCode:154259924 MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=294.96265, y[0]=259.94922, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=39976162, downTime=39976162, deviceId=0, source=0x1002 }
2020-12-17 08:06:32.124 18401-18401/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:154259924 hashCode:154259924 MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=294.96265, y[0]=262.9375, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=39976199, downTime=39976162, deviceId=0, source=0x1002 }
2020-12-17 08:06:32.140 18401-18401/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:154259924 hashCode:154259924 MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=297.9619, y[0]=270.37024, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=3, eventTime=39976221, downTime=39976162, deviceId=0, source=0x1002 }
2020-12-17 08:06:32.153 18401-18401/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:154259924 hashCode:154259924 MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=297.9619, y[0]=277.14856, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=39976237, downTime=39976162, deviceId=0, source=0x1002 }
2020-12-17 08:06:32.179 18401-18401/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:154259924 hashCode:154259924 MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=297.9619, y[0]=283.97266, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=2, eventTime=39976253, downTime=39976162, deviceId=0, source=0x1002 }
2020-12-17 08:06:32.180 18401-18401/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:154259924 hashCode:154259924 MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=297.9619, y[0]=283.97266, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=39976265, downTime=39976162, deviceId=0, source=0x1002 }

测试二 - 不同的页面测试

//AActivity.java
2020-12-17 08:24:16.497 19018-19018/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:267645040 hashCode:267645040 MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=172.96875, y[0]=289.98047, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=41040583, downTime=41040583, deviceId=0, source=0x1002 }
2020-12-17 08:24:16.512 19018-19018/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:267645040 hashCode:267645040 MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=172.96875, y[0]=289.98047, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=41040601, downTime=41040583, deviceId=0, source=0x1002 }//BActivity.java
2020-12-17 08:24:49.738 19018-19018/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:267645040 hashCode:267645040 MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=410.96558, y[0]=277.96875, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=41073821, downTime=41073821, deviceId=0, source=0x1002 }
2020-12-17 08:24:49.792 19018-19018/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:267645040 hashCode:267645040 MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=410.96558, y[0]=277.96875, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=41073879, downTime=41073821, deviceId=0, source=0x1002 }

测试三同一个应用杀进程测试

//杀进程前
2020-12-17 08:25:40.127 19175-19175/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:267645040 hashCode:267645040 MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=366.96533, y[0]=380.97656, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=41124208, downTime=41124208, deviceId=0, source=0x1002 }
2020-12-17 08:25:40.216 19175-19175/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:267645040 hashCode:267645040 MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=366.96533, y[0]=380.97656, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=41124276, downTime=41124208, deviceId=0, source=0x1002 }//杀死进程后在启动测试
2020-12-17 08:26:55.298 19228-19228/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:267645040 hashCode:267645040 MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=193.96362, y[0]=432.94922, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=41199384, downTime=41199384, deviceId=0, source=0x1002 }
2020-12-17 08:26:55.336 19228-19228/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:267645040 hashCode:267645040 MotionEvent { action=ACTION_MOVE, actionButton=0, id[0]=0, x[0]=193.96362, y[0]=428.70605, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=1, eventTime=41199411, downTime=41199384, deviceId=0, source=0x1002 }
2020-12-17 08:26:55.360 19228-19228/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:267645040 hashCode:267645040 MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=193.96362, y[0]=429.96094, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=41199450, downTime=41199384, deviceId=0, source=0x1002 }

测试四不同进程

//com.example.viewtest进程
2020-12-17 08:39:09.508 19756-19756/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:149898054 hashCode:149898054 MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=202.96143, y[0]=362.9297, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=41933595, downTime=41933595, deviceId=0, source=0x1002 }
2020-12-17 08:39:09.593 19756-19756/com.example.viewtest D/zhangyu20201217: dispatchTouchEvent identityHashCode:149898054 hashCode:149898054 MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=202.96143, y[0]=362.9297, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=41933653, downTime=41933595, deviceId=0, source=0x1002 }//com.example.tw进程
2020-12-17 08:39:48.327 19847-19847/com.example.tw D/zhangyu20201217: dispatchTouchEvent identityHashCode:139330987 hashCode:139330987 MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=287.96265, y[0]=421.9336, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=41972412, downTime=41972412, deviceId=0, source=0x1002 }
2020-12-17 08:39:48.400 19847-19847/com.example.tw D/zhangyu20201217: dispatchTouchEvent identityHashCode:139330987 hashCode:139330987 MotionEvent { action=ACTION_UP, actionButton=0, id[0]=0, x[0]=287.96265, y[0]=421.9336, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=41972490, downTime=41972412, deviceId=0, source=0x1002 }

测试结果+总结

测试结果现象总结：

发现整个事件传递的流程中。【ACTION_DOWN】【ACTION_MOVE】【ACTION_UP】流中，MotionEvent 都是同一个对象。

就算不是同一个事件流，UP事件后再触发MotionEvent 跟之前还是同一个对象。

同一个进程不同页面间MotionEvent是同一个对象

同一进程后台杀死两次测试，MotionEvent是同一个对象

不同进程间的MotionEvent不是同一个对象

根据测试现象做结果分析：

同一个进程MotionEvent是同一个对象
不同进程MotionEvent不是同一个对象

源码分析

根据上面的测试，我们知道了在同一个进程中，MotionEvent是同一个对象。那么为什么？以及源码怎么实现的？
MotionEvent是同一个对象，我觉得，为了防止对象被重复创建，而且整个事件传递都是在主线程，不存在安全问题，只要每次事件源头同步好MotionEvent的状态就行。

根据源码：

    //MotionEvent.javaprivate static final Object gRecyclerLock = new Object();private static int gRecyclerUsed;private static MotionEvent gRecyclerTop;...private MotionEvent mNext;@UnsupportedAppUsagestatic private MotionEvent obtain() {final MotionEvent ev;synchronized (gRecyclerLock) {ev = gRecyclerTop;if (ev == null) {return new MotionEvent();}gRecyclerTop = ev.mNext;gRecyclerUsed -= 1;}ev.mNext = null;ev.prepareForReuse();return ev;}

MotionEvent.java中存在obtain方法（类似Handler的Message），该方法就是从缓存gRecyclerTop 中取出头部元素，没有就生成。然后gRecyclerTop 指向头部的下一个元素。等待下一次使用。而且gRecyclerTop是一个静态变量，在系统层面，是公用的。

    private static native long nativeInitialize(long nativePtr,int deviceId, int source, int displayId, int action, int flags, int edgeFlags,int metaState, int buttonState, @Classification int classification,float xOffset, float yOffset, float xPrecision, float yPrecision,long downTimeNanos, long eventTimeNanos,int pointerCount, PointerProperties[] pointerIds, PointerCoords[] pointerCoords);static public MotionEvent obtain(long downTime, long eventTime,int action, int pointerCount, PointerProperties[] pointerProperties,PointerCoords[] pointerCoords, int metaState, int buttonState,float xPrecision, float yPrecision, int deviceId,int edgeFlags, int source, int displayId, int flags) {MotionEvent ev = obtain();ev.mNativePtr = nativeInitialize(ev.mNativePtr,deviceId, source, displayId, action, flags, edgeFlags, metaState, buttonState,CLASSIFICATION_NONE, 0, 0, xPrecision, yPrecision,downTime * NS_PER_MS, eventTime * NS_PER_MS,pointerCount, pointerProperties, pointerCoords);...return ev;}

还提供了native方法nativeInitialize,复用时去native层把属性重新赋值。

以上就是我的分析。很多问题需要从源码中找到解决办法和一些处理问题的思路。

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【Android】为啥事件传递这么频繁却不会造成内存抖动

【Android】为啥事件传递这么频繁却不会造成内存抖动

引言

测试

测试代码

测试一两次手指按下起来

测试二 - 不同的页面测试

测试三同一个应用杀进程测试

测试四不同进程

测试结果+总结

源码分析

【Android】为啥事件传递这么频繁却不会造成内存抖动相关推荐

最新文章

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【Android】为啥事件传递这么频繁却不会造成内存抖动

【Android】为啥事件传递这么频繁却不会造成内存抖动

引言

测试

测试代码

测试一 两次手指按下起来

测试二 - 不同的页面测试

测试三 同一个应用杀进程测试

测试四 不同进程

测试结果+总结

源码分析

【Android】为啥事件传递这么频繁却不会造成内存抖动相关推荐

最新文章

热门文章

测试一两次手指按下起来

测试三同一个应用杀进程测试

测试四不同进程