android绘制触点轨迹的代码

 /**  * Return the kind of action being performed.  * Consider using {@link #getActionMasked} and {@link #getActionIndex} to retrieve  * the separate masked action and pointer index.  * @return The action, such as {@link #ACTION_DOWN} or  * the combination of {@link #ACTION_POINTER_DOWN} with a shifted pointer index.  */ public final int getAction() {  return nativeGetAction(mNativePtr);//注意返回值表达式 }

 public static final int ACTION_POINTER_INDEX_MASK = 0xff00; public static final int ACTION_POINTER_INDEX_SHIFT = 8; /**  * For {@link #ACTION_POINTER_DOWN} or {@link #ACTION_POINTER_UP}  * as returned by {@link #getActionMasked}, this returns the associated  * pointer index.  * The index may be used with {@link #getPointerId(int)},  * {@link #getX(int)}, {@link #getY(int)}, {@link #getPressure(int)},  * and {@link #getSize(int)} to get information about the pointer that has  * gone down or up.  * @return The index associated with the action.  */ public final int getActionIndex() { //这个表达式实际就是说取getAction()函数返回值的高8位  return (nativeGetAction(mNativePtr) & ACTION_POINTER_INDEX_MASK)    >> ACTION_POINTER_INDEX_SHIFT; }

 public static final int ACTION_MASK    = 0xff; /**  * Return the masked action being performed, without pointer index information.  * Use {@link #getActionIndex} to return the index associated with pointer actions.  * @return The action, such as {@link #ACTION_DOWN} or {@link #ACTION_POINTER_DOWN}.  */ public final int getActionMasked() { //这个表达式的意思就是说取getAction()函数的低8位  return nativeGetAction(mNativePtr) & ACTION_MASK; }

//注意函数的注释第一句的说明，表示，返回的id叫pointer identifier,是和event里面的数据关联的 /**  * Return the pointer identifier associated with a particular pointer  * data index in this event. The identifier tells you the actual pointer  * number associated with the data, accounting for individual pointers  * going up and down since the start of the current gesture.  * @param pointerIndex Raw index of pointer to retrieve. Value may be from 0  * (the first pointer that is down) to {@link #getPointerCount()}-1.  */ public final int getPointerId(int pointerIndex) {  return nativeGetPointerId(mNativePtr, pointerIndex); }

 //注意函数的注释里面第一句，意思是提供一个pointer identifier,返回event中对应数据的index //index of data的作用是传给event.getX()等其他的函数来获取坐标等信息 //所以这个函数的名字改成getPointerDataIndex比较合适 /**  * Given a pointer identifier, find the index of its data in the event.  *  * @param pointerId The identifier of the pointer to be found.  * @return Returns either the index of the pointer (for use with  * {@link #getX(int)} et al.), or -1 if there is no data available for  * that pointer identifier.  */ public final int findPointerIndex(int pointerId) {  return nativeFindPointerIndex(mNativePtr, pointerId); }

int index = event.getActionIndex();int id = event.getPointerId(index);int pointerIndex = event.findPointerIndex(id);int x=getX(pointerIndex);int y=getY(pointerIndex);

WindowManager manager=(WindowManager) getApplicationContext().getSystemService(Context.WINDOW_SERVICE);DisplayMetrics displayMetrics=new DisplayMetrics();Display display=manager.getDefaultDisplay();display.getMetrics(displayMetrics);screenW=displayMetrics.widthPixels;screenH=displayMetrics.heightPixels;

import android.content.Context;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.graphics.PorterDuff;import android.graphics.PorterDuffXfermode;import android.util.AttributeSet;import android.util.Log;import android.view.MotionEvent;import android.view.View;import java.util.HashMap;import java.util.Map;public class TouchTraceView extends View{ Context mContext; private Paint line_paint, text_paint, countPaint; int screenW, screenH; FactoryApplication app; private int paintColor = Color.RED; Map<Integer, TouchPoint> pointMap; float back_x1, back_y1, back_x2, back_y2; public TouchTraceView(Context context, AttributeSet attr) {  super(context, attr);  mContext = context;  app = ;//作用仅仅是获取默认屏幕的长和宽  this.screenH = app.screenH;  this.screenW = app.screenW;  pointMap = new HashMap<>();  initPaint(); } private void initPaint() {  line_paint = new Paint();  line_paint.setAntiAlias(true);  line_paint.setColor(paintColor);  text_paint = new Paint();  text_paint.setAntiAlias(true);  text_paint.setColor(Color.BLUE);  text_paint.setTextSize(30);  countPaint = new Paint();  countPaint.setAntiAlias(true);  countPaint.setColor(Color.GREEN);  countPaint.setTextSize(60); } @Override protected void onDraw(Canvas canvas) {  super.onDraw(canvas);  int num = pointMap.size();  if (num == 0)  {   clearDraw(canvas);   return;  }  for (Map.Entry<Integer, TouchPoint> entry : pointMap.entrySet())  {   TouchPoint point = entry.getValue();   canvas.drawLine(0, point.y, getWidth(), point.y, line_paint);   canvas.drawLine(point.x, 0, point.x, getHeight(), line_paint);   if (num == 1)   {    canvas.drawText(" (" + point.x + "," + point.y + ")", screenW / 2, screenH / 2, text_paint);   } else   {    canvas.drawText(String.valueOf(pointMap.size()), screenW / 2, screenH / 2, countPaint);   }  } } @Override public boolean onTouchEvent(MotionEvent event) {  int index = event.getActionIndex();  int id = event.getPointerId(index);  int pointerIndex = event.findPointerIndex(id);  int pointerCount = event.getPointerCount();  int historySize = event.getHistorySize();  switch (event.getActionMasked())  {   case MotionEvent.ACTION_POINTER_DOWN:    pointMap.put(pointerIndex, new TouchPoint(event.getX(pointerIndex), event.getY(pointerIndex)));    break;   case MotionEvent.ACTION_POINTER_UP:    pointMap.remove(pointerIndex);    break;   case MotionEvent.ACTION_MOVE:    for (int h = 0; h < historySize; h++)    {     for (int p = 0; p < pointerCount; p++)     {      pointMap.put(p, new TouchPoint(event.getHistoricalX(p, h), event.getHistoricalY(p, h)));     }    }    for (int p = 0; p < pointerCount; p++)    {     pointMap.put(p, new TouchPoint(event.getX(p), event.getY(p)));    }    break;   case MotionEvent.ACTION_DOWN:    pointMap.put(0, new TouchPoint(event.getX(pointerIndex), event.getY(pointerIndex)));    back_x1 = event.getX();    back_y1 = event.getY();    break;   case MotionEvent.ACTION_UP:    back_x2 = event.getX();    back_y2 = event.getY();    if (Math.abs(back_x1 - back_x2) > screenW / 2 && Math.abs(back_y1 - back_y2) > screenH / 2)    {     callOnClick();    }    pointMap.clear();    break;   default:    break;  }  if (event.getPointerCount() == 0) pointMap.clear();  invalidate();  return true; } class TouchPoint {  public float x = 0;  public float y = 0;  TouchPoint(float x, float y)  {   this.x = x;   this.y = y;  } } void clearDraw(Canvas canvas) {  Paint paint = new Paint();  paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));  canvas.drawPaint(paint);  paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC));  canvas.drawColor(Color.WHITE); }}