Android觸摸事件如何實現筆觸畫布詳解

2019-10-21 21:36:30

字體：大中小

來源：轉載

供稿：網友

前言

任何View都有觸摸事件,經常在自定義控件時重寫setOnTouchListener

本篇通過手繪圖片來講述這個知識點，下面話不多說了，來一起看看詳細的介紹吧

本篇分為三個等級：一覽圖：

直線

Android,觸摸事件,筆觸畫布

曲線

Android,觸摸事件,筆觸畫布

筆觸

Android,觸摸事件,筆觸畫布

LEVEL1:基礎實現

在Activity中通過一個全屏的Bitmap創建的Canvas繪制

為ImageView添加觸摸事件監聽。

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.創建畫布

//獲取屏幕尺寸Point point = new Point();getWindowManager().getDefaultDisplay().getSize(point);//創建一個和屏幕一樣大的BitmapBitmap bitmap = Bitmap.createBitmap(point.x, point.y, Bitmap.Config.ARGB_8888);//創建Canvas對象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;  }); }

升級版：LEVER2

Android,觸摸事件,筆觸畫布

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();   //更新點位   downY = upY;   downX = upX;   break;  case MotionEvent.ACTION_UP:   //抬起點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;});

再升級版：LEVER3

筆觸根據繪制的速度動態改變畫筆粗細

Android,觸摸事件,筆觸畫布

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

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();   //計算時間差   long detaT = curTimestamp - lastTimestamp;   //計算距離差   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現不同的筆觸:如

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

Android,觸摸事件,筆觸畫布

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"));//設置副本圖片到ImageViewmIdIvShow.setImageBitmap(mNewBitmap);

Android,觸摸事件,筆觸畫布