Android触摸事件如何实现笔触画布详解

2019-10-21 21:36:30

字体：大中小

来源：转载

供稿：网友

前言

任何View都有触摸事件,经常在自定义控件时重写setOnTouchListener

本篇通过手绘图片来讲述这个知识点，下面话不多说了，来一起看看详细的介绍吧

本篇分为三个等级：一览图：

直线

Android,触摸事件,笔触画布

曲线

Android,触摸事件,笔触画布

笔触

Android,触摸事件,笔触画布

LEVEL1:基础实现

在Activity中通过一个全屏的Bitmap创建的Canvas绘制

为ImageView添加触摸事件监听。

1.成员变量

ImageView mIdIvShow;float downX = 0;float downY = 0;float upX = 0;float upY = 0;private Canvas mCanvas;private Paint mPaint;

2.创建画布

//获取屏幕尺寸Point point = new Point();getWindowManager().getDefaultDisplay().getSize(point);//创建一个和屏幕一样大的BitmapBitmap bitmap = Bitmap.createBitmap(point.x, point.y, Bitmap.Config.ARGB_8888);//创建Canvas对象mCanvas = new Canvas(bitmap);mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);mPaint.setStrokeWidth(10);mPaint.setColor(Color.RED);//将bitmap用ImageView展示mIdIvShow.setImageBitmap(bitmap);

3.监听事件

 mIdIvShow.setOnTouchListener((v, event) -> {   switch (event.getAction()) {    case MotionEvent.ACTION_DOWN:     downX = event.getX();     downY = event.getY();     L.d("按下:(" + downX + "," + downY + ")" + L.l());     break;    case MotionEvent.ACTION_CANCEL:     break;    case MotionEvent.ACTION_MOVE:     break;    case MotionEvent.ACTION_UP:     upX = event.getX();     upY = event.getY();     L.d("抬起:(" + upX + "," + upY + ")" + L.l());     mCanvas.drawLine(downX, downY, upX, upY, mPaint);     mIdIvShow.invalidate();//更新视图     break;   }   return true;  }); }

升级版：LEVER2

Android,触摸事件,笔触画布

mIdIvShow.setOnTouchListener((v, event) -> { switch (event.getAction()) {  case MotionEvent.ACTION_DOWN:   downX = event.getX();   downY = event.getY();   break;  case MotionEvent.ACTION_CANCEL:   break;  case MotionEvent.ACTION_MOVE:   upX = event.getX();   upY = event.getY();   mCanvas.drawLine(downX, downY, upX, upY, mPaint);   mIdIvShow.invalidate();   //更新点位   downY = upY;   downX = upX;   break;  case MotionEvent.ACTION_UP:   //抬起点Y>1100,清除笔迹   if (upY > 1100) {    Paint paint = new Paint();    paint.setColor(Color.WHITE);    mCanvas.drawRect(0, 0, mPoint.x, mPoint.y, paint);   }   break; } return true;});

再升级版：LEVER3

笔触根据绘制的速度动态改变画笔粗细

Android,触摸事件,笔触画布

float movingX = 0;float movingY = 0;private long lastTimestamp = 0L;//最后一次的时间戳

mIdIvShow.setOnTouchListener((view, event) -> { switch (event.getAction()) {  case MotionEvent.ACTION_DOWN:   lastTimestamp = System.currentTimeMillis();   downX = event.getX();   downY = event.getY();   break;  case MotionEvent.ACTION_CANCEL:   break;  case MotionEvent.ACTION_MOVE:   movingX = event.getX();   movingY = event.getY();   long curTimestamp = System.currentTimeMillis();   //计算时间差   long detaT = curTimestamp - lastTimestamp;   //计算距离差   float detaS = Logic.disPos2d(movingX, movingY, downX, downY);   //由于速度是 px/ms   double v = detaS / detaT;   //速度转化为画笔宽度的等式   float width = 14/(float)v;   L.d(width + L.l());   //限制极值情况   if ((width > 0) && width < 30) {    mPaint.setStrokeWidth(width);   }   mCanvas.drawLine(downX, downY, movingX, movingY, mPaint);   mIdIvShow.invalidate();   downX = movingX;   downY = movingY;   lastTimestamp = curTimestamp;//更新时间   movePos.add(new PointF(event.getX(), event.getY()));   break; } return true;});

拓展

1.其中可以改变求宽度的等式实现不同的笔触:如

float width = (float) Math.log10(v) * 40;

Android,触摸事件,笔触画布

2.在图片上绘画

//图片原型Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.iv_500x400);//图片副本Bitmap mNewBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), bitmap.getConfig());//用副本生成CanvasmCanvas = new Canvas(mNewBitmap);mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);mPaint.setStrokeCap(Paint.Cap.ROUND);//直线圆头mCanvas.drawBitmap(bitmap, new Matrix(), mPaint);mPaint.setStrokeWidth(10);mPaint.setColor(Color.parseColor("#88164BE6"));//设置副本图片到ImageViewmIdIvShow.setImageBitmap(mNewBitmap);

Android,触摸事件,笔触画布