自定义view，实现特殊拖动条

一个简单的拖动条，类似ruler，先上图

11281318-1f0dc2c91434c62c.png

演示用，所以很多细节如自定义属性，惯性滑动等没做，直接上代码，有注释：

public class RegulateView extends View {
    private int radius_normal = DensityUtil.dp2px(2);//大圆半径
    private int radius_big = DensityUtil.dp2px(3);//小圆半径
    private Paint mPaint;//小圆画笔
    private Paint pink_paint;//大圆画笔
    private int gap = radius_normal * 5;//间距
    private int itemCount = 100;//刻度
    private int w, h;
    private float startX;//起始绘制坐标x
    private float startY;//起始绘制坐标y
    private Paint mTextPaint;//text

    public RegulateView(Context context) {
        this(context, null);
    }

    public RegulateView(Context context, @androidx.annotation.Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public RegulateView(Context context, @androidx.annotation.Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }


    public void setProgress(float index) {
        this.index = index;
        startX = centerX - (index + itemCount) * gap;
        invalidate();
    }

    private void init() {
        mPaint = new Paint();
        mPaint.setColor(Color.BLACK);
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);

        pink_paint = new Paint();
        pink_paint.setColor(Color.RED);
        pink_paint.setAntiAlias(true);
        pink_paint.setDither(true);

        mTextPaint = new Paint();
        mTextPaint.setTextSize(DensityUtil.dp2px(10));
        mTextPaint.setColor(Color.RED);
        mTextPaint.setTextAlign(Paint.Align.CENTER);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int width = MeasureSpec.getSize(widthMeasureSpec);
        int height = MeasureSpec.getSize(heightMeasureSpec);
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        if (widthMode != MeasureSpec.EXACTLY) {
            width = getMeasuredWidth() * 3 / 4 - getPaddingLeft() - getPaddingRight();
        }

        if (heightMode != MeasureSpec.EXACTLY) {
            height = DensityUtil.dp2px(5) * 8;
        }

        setMeasuredDimension(width, height);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        float start = startX;
        for (int i = -itemCount; i <= itemCount; i++) {
            if (i % 5 == 0) {
                //给一个范围，屏幕中心点设为选中点
                if (start < centerX + (float) gap / 2 && start > centerX - (float) gap / 2) {
                    canvas.drawCircle(start, startY, radius_big, pink_paint);
                } else
                    canvas.drawCircle(start, startY, radius_big, mPaint);
            } else {
                if (start < centerX + (float) gap / 2 && start > centerX - (float) gap / 2) {
                    canvas.drawCircle(start, startY, radius_normal, pink_paint);
                } else
                    canvas.drawCircle(start, startY, radius_normal, mPaint);
            }
            start += gap;
        }
        canvas.drawText((int)index + "%", centerX, startY - radius_big*2, mTextPaint);
    }

    float index;
    float lastX;
    float centerX;
    float centerY;

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                lastX = event.getX();
                break;
            case MotionEvent.ACTION_MOVE:
                float swipeDistance = event.getX() - lastX;
                startX += swipeDistance;
                //限制右边界
                if (startX <= w / 2 - itemCount * gap * 2) {
                    startX = centerX - itemCount * gap * 2;
                }
                //限制滚动左边界
                if (startX >= w / 2) {
                    startX = centerX;
                }


                index = (centerX - startX - itemCount * gap) / gap;
                int progress = floatToInt(index);
                if (mListener != null)
                    mListener.onScroll(progress);
                lastX = event.getX();
                invalidate();
                break;
            case MotionEvent.ACTION_UP:

                break;
        }
        return true;
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        this.w = w;
        this.h = h;
        centerX = (float) w / 2;
        centerY = (float) h / 2 + radius_big*2;
        startX = centerX - itemCount * gap;
        startY = centerY;
    }

    private onProgressScrollListener mListener;

    public onProgressScrollListener getListener() {
        return mListener;
    }

    public void setListener(onProgressScrollListener listener) {
        mListener = listener;
    }

    public interface onProgressScrollListener {
        void onScroll(int index);
    }

//四舍五入
    private int floatToInt(float f) {
        int i = 0;
        if (f > 0)
            i = (int) ((f * 10 + 5) / 10);
        else if (f < 0)
            i = (int) ((f * 10 - 5) / 10);
        else i = 0;
        return i;
    }

}