自定义视图drawArc，检测用户触摸弧的绘制路径

Question

我正在创建一个自定义视图，这是一种圆弧滑块进度视图。我可以根据用户触摸的位置（在x轴上）通过计算扫描绘制更多或更少的弧，我首先执行此操作计算用户沿x轴触摸的百分比.0％将一直向左，100％将一直向右。

我想更进一步，而不是根据用户按下的x坐标绘制弧线，我想让它仅在用户触摸实际弧线绘制路径时移动，因此更加逼真。我仍然是新的自定义视图，我的数学是有限的，但如果我得到一些提示，我将不胜感激

class ArcProgress extends View {

    Context cx;
    float width;

    float height;
    float center_x, center_y;
    final RectF oval = new RectF();
    final RectF touchArea = new RectF();

    float sweep = 0;
    float left, right;
    int percent = 0;

    public ArcProgress(Context context) {
        super(context);
        cx = context;

    }

    public int getPercentage() {
        return percent;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        setBackgroundColor(0xfff0ebde);

        width = (float) getWidth();
        height = (float) getHeight();

        float radius;

        if (width > height) {
            radius = height / 3;
        } else {
            radius = width / 3;
        }

        Paint paint = new Paint();
        paint.setAntiAlias(true);
        paint.setColor(0xffd2c8b6);
        paint.setStrokeWidth(35);

        paint.setStyle(Paint.Style.STROKE);

        center_x = width / 2;
        center_y = height / 2;

        left = center_x - radius;
        float top = center_y - radius;
        right = center_x + radius;
        float bottom = center_y + radius;

        oval.set(left, top, right, bottom);

            //this is the background arc, it remains constant
        canvas.drawArc(oval, 180, 180, false, paint);

        paint.setStrokeWidth(10);
        paint.setColor(0xffe0524d);
            //this is the red arc whichhas its sweep argument manipulated by on touch
        canvas.drawArc(oval, 180, sweep, false, paint);

    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {

        if (event.getAction() == MotionEvent.ACTION_MOVE) {

            float xPosition = event.getX();
            float yPosition = event.getY();
            if (oval.contains(xPosition, yPosition)) {

                float x = xPosition - left;
                float s = x * 100;
                float b = s / oval.width();
                percent = Math.round(b);
                sweep = (180 / 100.0f) * (float) percent;

                invalidate();

            } else {
                if (xPosition < left) {
                    percent = 0;

                    sweep = (180 / 100.0f) * (float) percent;
                    invalidate();
                }
                if (xPosition > right) {
                    percent = 100;

                    sweep = (180 / 100.0f) * (float) percent;
                    invalidate();
                }
            }
        }

        return true;
    }
}

Answer 1

  

我想仅在用户触摸实际弧时才移动它   画路径

在onTouchEvent()开始时，您需要检查xPosition和yPosition是否符合某些条件。如果是的话，你会做你现在正在做的事情。如果不是，return true。

<强>条件：

我们想检查x，y是否在灰色弧背景中：

让我们计算中心距（x，y）到该点（a，b）的距离：

final dist = distance(x, y, a, b)

distance()是点（x，y）和（a，b）之间的简单欧几里德距离：

double distance(int x, int y, int a, int b)
{
    return Math.sqrt((x - a) * (x - a) + (y - b) * (y - b));
}

x，y位于灰色弧背景中，如果y > Y && dist >= r && dist <= R。

Answer 2

这对你有用吗？ 你不需要很多数学。您可以计算触点与弧中心的距离（它是一个圆圈，因此很容易），并与您正在使用的半径进行比较。这将告诉你点是否在弧上（几乎，见下面的完整情况）。

Point touchEv = ...; 
Point circleCenter = ...; 

//the radius of the circle you used to draw the arc
float circleRadius = ...; 
//how far from the arc should a touch point treated as it's on the arc
float maxDiff = getResources().getDimension(R.dimen.max_diff_dp);

//calculate the distance of the touch point from the center of your circle
float dist = Math.pow(touchEv.x-circleCenter.x,2) + Math.pow(touchEv.y-  circleCenter.y,2)
dist = Math.sqrt(dist); 

//We also need the bounding rect of the top half of the circle (the visible arc)
Rect topBoundingRect = new Rect(circleCenter.x - circleRadius,
            circleCenter.y - circleRadius, 
            circleCenter.x + circleRadius,
            circleCenter.y);


if (Math.abs(dist - circleRadius)  <= maxDiff  &&
  topBoundingRect.contains(touchEv.x, touchEv.y)) {
  // the user is touching the arc 

}