1、最近公司项目有个需求是要做草稿纸功能，花了点时间完成了这个功能，顺便自己记录一下

2、大体思路是用画笔对按下和移动的路径进行描边，然后画出，抬起之后保存这个路径和画笔，以供后期要删除使用

3、下面上代码

//初始化画笔
    private void init(Context context) {
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG | Paint.DITHER_FLAG);
        //画笔是空心的
        mPaint.setStyle(Paint.Style.STROKE);
        //画笔的笔尖 这里是圆形
        mPaint.setStrokeCap(Paint.Cap.ROUND);
//        Join.MITER（结合处为锐角）
//        Join.Round(结合处为圆弧)
//        Join.BEVEL(结合处为直线)
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        //处理图片
        mPaint.setFilterBitmap(true);
        //设置画笔的宽度
        mPaint.setStrokeWidth(5);
        //设置画笔颜色
        mPaint.setColor(Color.BLACK);


    }
    
    
    ...
        //取消撤回功能
    public void redo() {
        int size = mRemoveList == null ? 0 : mRemoveList.size();
        if (size > 0) {
            DrawInfo info = mRemoveList.remove(size - 1);
            mDrawList.add(info);
            reDraw();
        }
    }
    
        //撤回
    public void undo() {
        int size = mDrawList == null ? 0 : mDrawList.size();
        if (size > 0) {
            DrawInfo info = mDrawList.remove(size - 1);
            mRemoveList.add(info);
            reDraw();
        }
    }
    
        //清除
    public void clear() {
        if (mDrawList != null && mRemoveList != null) {
            mRemoveList.clear();
            mDrawList.clear();
            if (mBufferBitmap != null) {
                mBufferBitmap.eraseColor(Color.TRANSPARENT);
                invalidate();
            }
        }
    }
    
    //重新绘制
    private void reDraw() {
        if (mDrawList != null) {
            //把原来绘制在bitmap上的痕迹全部设置为透明,类似擦除
            mBufferBitmap.eraseColor(Color.TRANSPARENT);
            for (DrawInfo drawInfo : mDrawList) {
                //对mDrawList集合中的元素重新画上去
                drawInfo.draw(mBufferCanvas);
            }
            invalidate();
        }
    }
        @Override
    public boolean onTouchEvent(MotionEvent event) {
//        PointF midPoint = getMidPointOfFinger(event);
        int action = event.getAction() & MotionEvent.ACTION_MASK;
        float x = event.getX();
        float y = event.getY();
        switch (action) {
            case MotionEvent.ACTION_DOWN:
                mCanDrag = false;
                DownX = x;
                DownY = y;
                if (mPath == null) {
                    mPath = new Path();
                }
                mPath.moveTo(x, y);
                break;
            case MotionEvent.ACTION_MOVE:

//                if (mCanDrag) {
//                    x = event.getX();
//                    y = event.getY();
//                    float dx = x - DownX;
//                    float dy = y - DownY;
//                    mBufferMatrix.preTranslate((float) (dx * 0.05), (float) (dy * 0.05));
//                    invalidate();
//                    return true;
//                }
                mPath.quadTo(DownX, DownY, (x + DownX) / 2, (y + DownY) / 2);
                if (mBufferBitmap == null) {
                    initBuffer();
                }
                mBufferCanvas.drawPath(mPath, mPaint);
                invalidate();
                DownX = x;
                DownY = y;
                break;
            case MotionEvent.ACTION_UP:

                DownX = x;
                DownY = y;
                saveDraw();
                mPath.reset();
                break;
//            case MotionEvent.ACTION_POINTER_DOWN:
            
        return true;
    }
        //清除
    public void clear() {
        if (mDrawList != null && mRemoveList != null) {
            mRemoveList.clear();
            mDrawList.clear();
            if (mBufferBitmap != null) {
                mBufferBitmap.eraseColor(Color.TRANSPARENT);
                invalidate();
            }
        }
    }
    

核心代码就这些了 画板功能还是比较简单的