android 刻度尺控件实现

主要实现刻度尺的效果，能够快速滑动刻度，设置刻度间距，刻度值，滑动回调。简单易用

效果图

textureView控件的选择

刻度尺要不停的绘制，所以view是不可取的，这篇文章介绍了textureview的用法，受益匪浅

总结来说:

1.view的绘制在主线程里面，频繁绘制会导致主线程阻塞

2.我们知道一个surfaceview是异步绘制的，不阻塞主线程，但是它不支持平移、缩放、旋转，且很难放在srollview等控件里面

TextureView.SurfaceTextureListener

abstract void	onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) Invoked when a   TextureView's SurfaceTexture is ready for use.
abstract boolean	onSurfaceTextureDestroyed(SurfaceTexture surface) Invoked when the specified   SurfaceTexture  is about to be destroyed.  //textureview销毁时，可以在这个地方释放一些资源，比如camera
abstract void	onSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height) Invoked when the   SurfaceTexture's buffers size changed.
abstract void	onSurfaceTextureUpdated(SurfaceTexture surface) Invoked when the specified   SurfaceTexture  is updated through   updateTexImage().

@Override
    public void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {
        mBorderRectF.set(mBorderPaint.getStrokeWidth(), mBorderPaint.getStrokeWidth(),
                width - mBorderPaint.getStrokeWidth(), height - mBorderPaint.getStrokeWidth());  //设置一块矩形区域，
        mWidth = mBorderRectF.width();  
        dis = (int)(mWidth / allBlockNum);  //每个刻度间距,allBlockNum是小刻度的个数
        refreshCanvas(); 
    }

//刷新视图 
    private void refreshCanvas() {
        if (mBorderRectF.isEmpty()) {
            return;
        }
        Canvas canvas = lockCanvas();
        if(canvas != null) {
            canvas.drawColor(Color.WHITE);
            drawBorder(canvas);
            drawScaleMark(canvas);
            drawMarkPoint(canvas);
        }
        unlockCanvasAndPost(canvas);
    }

画出刻度线:由中间向两边画

//画出所有刻度:从中间向两边画
    private void drawScaleMark(Canvas canvas) {
        int count = 0;
        final int centerX = (int)mBorderRectF.centerX();
        if(mCenterNum > maxNum)
            mCenterNum = maxNum;
        if (mCenterNum < minNum)
            mCenterNum = minNum;
        if(numberListener != null)
            numberListener.onChanged(mCenterNum);

        while(true){
            int left = centerX - dis * count;
            int leftNum = mCenterNum - count * scaleNum;
            int right = centerX + dis * count;
            int rightNum = mCenterNum + count * scaleNum;

            String leftText = String.valueOf(leftNum);
            String rightText = String.valueOf(rightNum);
            //间隔5刻度画文字信息
            if(leftNum % (5*scaleNum) == 0) {
                canvas.drawLine(left, canvas.getHeight() / 2, left, canvas.getHeight() - 1, mScaleMarkPaint);
                mScaleMarkPaint.getTextBounds(leftText, 0, leftText.length(), mTextRect);
                canvas.drawText(leftText, left - mTextRect.centerX(), canvas.getHeight() / 2, mScaleMarkPaint);
            }
            else
                canvas.drawLine(left, canvas.getHeight() * 2 / 3, left, canvas.getHeight() - 1, mScaleMarkPaint);

            if(rightNum % (5*scaleNum) == 0) {
                canvas.drawLine(right, canvas.getHeight() / 2, right, canvas.getHeight() - 1, mScaleMarkPaint);
                mScaleMarkPaint.getTextBounds(rightText, 0, rightText.length(), mTextRect);
                canvas.drawText(rightText, right - mTextRect.centerX(), canvas.getHeight() / 2, mScaleMarkPaint);
            }
            else
                canvas.drawLine(right, canvas.getHeight() * 2 / 3, right, canvas.getHeight() - 1, mScaleMarkPaint);

            count++;
            if(left < 0)
                break;
        }
    }

手势判断

我把手势判断的逻辑代码写在ScaleScroller类中，onTouchEvent用来判断按下，移动和抬起三个手势。GestureDetector.SimpleOnGestureListener中的onFling来处理快速滑动

OnFling在手指快速滑动控件时触发，onfling有四个参数

(注意:onFling只能触发一次,但是快速滑动的效果是要在一定时间内做滚动处理，所以需要通过Scroller类+Handler的方式来帮助实现)

@Override
        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
            final int minX = -0x7fffffff;
            final int maxX = 0x7fffffff;
            lastX = 0;
            scroller.fling(0, 0, (int)-velocityX, 0, minX, maxX, 0, 0);  //滚动的距离有速度决定
            handler.sendEmptyMessage(ON_FLING);
            return true;
        }

e1	The first down motion event that started the fling.       //按下时候的event
e2	The move motion event that triggered the current onFling.  //触发快速滑动时的event
velocityX	The velocity of this fling measured in pixels per second along the x axis.
velocityY	The velocity of this fling measured in pixels per second along the y axis.

private Handler handler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            boolean isFinished = scroller.computeScrollOffset(); //判断滚动是否结束
            int curX = scroller.getCurrX();  
            int delta = lastX - curX;
            if(listener != null){
                listener.onScroll(delta);
            }
            lastX = curX;
            if(isFinished)
                handler.sendEmptyMessage(ON_FLING);  
            else
                listener.onFinished();
        }
    };

源码地址