如何在BulletSpan中将项目符号半径设置为低于api级别28？

import android.graphics.Canvas;
import android.graphics.Paint;
import android.text.Layout;
import android.text.style.BulletSpan;

public class CustomBulletSpan extends BulletSpan {
    private static final int DEFAULT_RADIUS = 10; // 自定义的项目符号半径

    public CustomBulletSpan() {
        super(DEFAULT_RADIUS);
    }

    @Override
    public void drawLeadingMargin(Canvas c, Paint p, int x, int dir, int top, int baseline, int bottom,
                                  CharSequence text, int start, int end, boolean first, Layout layout) {
        if (layout.getParagraphDirection(layout.getLineForOffset(start)) == Layout.DIR_RIGHT_TO_LEFT) {
            dir = -1;
        } else {
            dir = 1;
        }

        int oldColor = p.getColor();
        p.setColor(p.linkColor);

        c.drawCircle(x + dir * DEFAULT_RADIUS, (top + bottom) / 2.0f, DEFAULT_RADIUS, p);

        p.setColor(oldColor);
    }
}

SpannableString spannableString = new SpannableString("This is a bullet list");
spannableString.setSpan(new CustomBulletSpan(), 0, spannableString.length(), Spanned.SPAN_INCLUSIVE_EXCLUSIVE);
textView.setText(spannableString);