先贴效果图

image.png

图中的小圆点是可以随着手指的滑动, 绕着绿色的圆移动的哦
这个demo只是实现了部分功能, 但是手指跟随圆移动的逻辑很好玩..
贴代码:
public class CycleView extends View {

private int mMaxProcess = 30;

private int mCurrentProcess = 5;

private static final double RADIAN = 180 / Math.PI;

private Context mContext;

private Paint mBigCyclePaint;

private Paint mMiddleCyclePaint;

private Paint mSmallCyclePaint;

private double mCurrentAngle;

private int mBigCycleradius = 400;

private float mWheelCurX, mWheelCurY;

private CurrentProcessListener mCurrentProcessListener;

public void setmCurrentProcessListener(CurrentProcessListener mCurrentProcessListener) {
    this.mCurrentProcessListener = mCurrentProcessListener;
}

interface CurrentProcessListener {
    void current(int current);
}

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

public CycleView(Context context, AttributeSet attrs) {
    this(context, attrs, 0);
}

public CycleView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    init(context, attrs);
}

/**
 * 初始化
 *
 * @param context
 * @param attrs
 */
private void init(Context context, AttributeSet attrs) {
    this.mContext = context;
    mBigCyclePaint = new Paint();
    mBigCyclePaint.setColor(Color.GREEN);
    mBigCyclePaint.setFlags(Paint.ANTI_ALIAS_FLAG);
    mBigCyclePaint.setStyle(Paint.Style.STROKE);
    mBigCyclePaint.setStrokeWidth(10);

    mMiddleCyclePaint = new Paint();
    mMiddleCyclePaint.setColor(Color.BLUE);
    mMiddleCyclePaint.setFlags(Paint.ANTI_ALIAS_FLAG);
    mMiddleCyclePaint.setStyle(Paint.Style.STROKE);
    mMiddleCyclePaint.setStrokeWidth(10);

    mSmallCyclePaint = new Paint();
    mSmallCyclePaint.setColor(Color.RED);
    mSmallCyclePaint.setFlags(Paint.ANTI_ALIAS_FLAG);
}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    int width = getWidth();
    int height = getHeight();
    canvas.drawCircle(width / 2, height / 2, mBigCycleradius, mBigCyclePaint);

    canvas.drawCircle(width / 2 + 80, height / 2 + 80, 260, mMiddleCyclePaint);

    canvas.drawCircle(mWheelCurX, mWheelCurY, 60, mSmallCyclePaint);

}

@Override
public boolean onTouchEvent(MotionEvent event) {
    float x = event.getX();
    float y = event.getY();
    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
        case MotionEvent.ACTION_MOVE:
            float cos = computeCos(x, y);
            //1, 算出点击的度数
            if (x < getWidth() / 2) { // 滑动超过180度
                mCurrentAngle = Math.PI * RADIAN + Math.acos(cos) * RADIAN;
            } else { // 没有超过180度
                mCurrentAngle = Math.PI * RADIAN - Math.acos(cos) * RADIAN;
            }
            //有了角度,

            refershWheelCurPosition(cos);//重装小圆点的位置
            if (mCurrentProcessListener != null) {
                //把当前的角度改了,
                //开始的角度, 应该是135°
                double angle = 0;
                if (mCurrentAngle < 135) {
                    angle = mCurrentAngle + (360-135);
                } else {
                    angle = mCurrentAngle - 135;
                }
                mCurrentProcess = (int) (angle / 360 * mMaxProcess);
                mCurrentProcessListener.current(mCurrentProcess);
            }
            invalidate();
            break;
        case MotionEvent.ACTION_UP:

            break;
    }
    return true;
}
private void refershWheelCurPosition(double cos) {
    mWheelCurX = calcXLocationInWheel(mCurrentAngle, cos);
    mWheelCurY = calcYLocationInWheel(cos);
}

private float calcXLocationInWheel(double angle, double cos) {
    if (angle < 180) {
        return (float) (getMeasuredWidth() / 2 + Math.sqrt(1 - cos * cos) * mBigCycleradius);
    } else {
        return (float) (getMeasuredWidth() / 2 - Math.sqrt(1 - cos * cos) * mBigCycleradius);
    }
}

private float calcYLocationInWheel(double cos) {
    return getMeasuredHeight() / 2 + mBigCycleradius * (float) cos;
}

/**
 * 拿到倾斜的cos值
 */
private float computeCos(float x, float y) {
    float width = x - getWidth() / 2;
    float height = y - getHeight() / 2;
    float slope = (float) Math.sqrt(width * width + height * height);
    return height / slope;
}

}