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 voidonSurfaceTextureAvailable(SurfaceTexture surface, int width, int height)

Invoked when a TextureView's SurfaceTexture is ready for use.  

abstract booleanonSurfaceTextureDestroyed(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 voidonSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height)

Invoked when the SurfaceTexture's buffers size changed.

abstract voidonSurfaceTextureUpdated(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;        }

e1The first down motion event that started the fling.       //按下时候的evente2The move motion event that triggered the current onFling.  //触发快速滑动时的eventvelocityXThe velocity of this fling measured in pixels per second along the x axis.velocityYThe 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