java - 自定义View drawArc，检测用户在弧形绘制路径上的触摸

Question

我正在创建一个自定义 View ，它是一种弧形 slider 进度 View 。我可以根据用户触摸的位置(在 x 轴上)通过计算扫描来绘制或多或少的弧形，我首先这样做计算用户沿 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 坐标绘制圆弧，我想让它仅在用户触摸实际圆弧绘制路径时移动，这样更逼真。我对自定义 View 还是新手，我的数学知识有限，但如果我能得到一些提示，我将不胜感激，谢谢

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

I want to make it move only when the user touches on the actual arc draw path

onTouchEvent()开头你需要检查是否xPosition和 yPosition正在满足某些条件。如果是，你就做你现在正在做的事情。如果没有，return true .

条件:

我们要检查 x, y 是否在那个灰色弧形背景中:

让我们计算从 (x, y) 到中心点 (a, b) 的距离:

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

distance()是点 (x,y) 和 (a,b) 之间的简单欧氏距离:

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

x, y 在那个灰色弧形背景中，如果 y > Y && dist >= r && dist <= R .