在安卓系统中更改BadgeDrawable字体

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Typeface;
import android.support.annotation.NonNull;
import android.support.v4.graphics.drawable.DrawableCompat;
import android.support.v7.widget.AppCompatImageView;
import android.util.AttributeSet;

public class CustomBadgeDrawable extends AppCompatImageView {

    private Paint textPaint;
    private String badgeText = "";
    private int badgeColor = Color.RED;
    private int badgeTextColor = Color.WHITE;
    private int badgeSize = 20;

    public CustomBadgeDrawable(Context context) {
        super(context);
        init();
    }

    public CustomBadgeDrawable(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        textPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        textPaint.setTextSize(12);
        textPaint.setColor(badgeTextColor);
        Typeface typeface = Typeface.create("sans-serif-medium", Typeface.NORMAL);
        textPaint.setTypeface(typeface);
    }

    public void setBadgeText(String text) {
        this.badgeText = text;
        invalidate();
    }

    public void setBadgeColor(int color) {
        this.badgeColor = color;
        invalidate();
    }

    public void setBadgeTextColor(int color) {
        this.badgeTextColor = color;
        invalidate();
    }

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

        if (!badgeText.isEmpty()) {
            int badgeWidth = (int) textPaint.measureText(badgeText) + badgeSize;
            int badgeHeight = badgeSize;

            int x = getWidth() - badgeWidth;
            int y = badgeHeight;

            canvas.drawCircle(x, y, badgeSize / 2, textPaint);
            canvas.drawText(badgeText, x + badgeSize / 2 - textPaint.measureText(badgeText) / 2, y + badgeSize / 2 + textPaint.getTextSize() / 2, textPaint);
        }
    }
}