Android觸摸事件如何實(shí)現(xiàn)筆觸畫布詳解

2019-12-12 00:28:22

字體：大中小

來源：轉(zhuǎn)載

供稿：網(wǎng)友

前言

任何View都有觸摸事件,經(jīng)常在自定義控件時(shí)重寫setOnTouchListener

本篇通過手繪圖片來講述這個(gè)知識(shí)點(diǎn)，下面話不多說了，來一起看看詳細(xì)的介紹吧

本篇分為三個(gè)等級(jí)：一覽圖：

直線

曲線

筆觸

LEVEL1:基礎(chǔ)實(shí)現(xiàn)

在Activity中通過一個(gè)全屏的Bitmap創(chuàng)建的Canvas繪制

為ImageView添加觸摸事件監(jiān)聽。

1.成員變量

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

2.創(chuàng)建畫布

//獲取屏幕尺寸Point point = new Point();getWindowManager().getDefaultDisplay().getSize(point);//創(chuàng)建一個(gè)和屏幕一樣大的BitmapBitmap bitmap = Bitmap.createBitmap(point.x, point.y, Bitmap.Config.ARGB_8888);//創(chuàng)建Canvas對(duì)象mCanvas = new Canvas(bitmap);mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);mPaint.setStrokeWidth(10);mPaint.setColor(Color.RED);//將bitmap用ImageView展示mIdIvShow.setImageBitmap(bitmap);

3.監(jiān)聽事件

 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();//更新視圖     break;   }   return true;  }); }

升級(jí)版：LEVER2

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();   //更新點(diǎn)位   downY = upY;   downX = upX;   break;  case MotionEvent.ACTION_UP:   //抬起點(diǎn)Y>1100,清除筆跡   if (upY > 1100) {    Paint paint = new Paint();    paint.setColor(Color.WHITE);    mCanvas.drawRect(0, 0, mPoint.x, mPoint.y, paint);   }   break; } return true;});

再升級(jí)版：LEVER3

筆觸根據(jù)繪制的速度動(dòng)態(tài)改變畫筆粗細(xì)

float movingX = 0;float movingY = 0;private long lastTimestamp = 0L;//最后一次的時(shí)間戳

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();   //計(jì)算時(shí)間差   long detaT = curTimestamp - lastTimestamp;   //計(jì)算距離差   float detaS = Logic.disPos2d(movingX, movingY, downX, downY);   //由于速度是 px/ms   double v = detaS / detaT;   //速度轉(zhuǎn)化為畫筆寬度的等式   float width = 14/(float)v;   L.d(width + L.l());   //限制極值情況   if ((width > 0) && width < 30) {    mPaint.setStrokeWidth(width);   }   mCanvas.drawLine(downX, downY, movingX, movingY, mPaint);   mIdIvShow.invalidate();   downX = movingX;   downY = movingY;   lastTimestamp = curTimestamp;//更新時(shí)間   movePos.add(new PointF(event.getX(), event.getY()));   break; } return true;});

拓展

1.其中可以改變求寬度的等式實(shí)現(xiàn)不同的筆觸:如

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

2.在圖片上繪畫

//圖片原型Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.iv_500x400);//圖片副本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);//直線圓頭mCanvas.drawBitmap(bitmap, new Matrix(), mPaint);mPaint.setStrokeWidth(10);mPaint.setColor(Color.parseColor("#88164BE6"));//設(shè)置副本圖片到ImageViewmIdIvShow.setImageBitmap(mNewBitmap);