Android 应用中怎么添加一个未读消息提示功能

  @SuppressWarnings("unused")  public static Drawable displayNewsNumber(Context context, int icon, int news) {   // 初始化画布   int iconSize = (int) context.getResources().getDimension(     android.R.dimen.app_icon_size);   // Bitmap contactIcon = Bitmap.createBitmap(iconSize, iconSize,   // Config.ARGB_8888);   Bitmap iconBitmap = BitmapFactory.decodeResource(     context.getResources(), icon);   Canvas canvas = new Canvas(iconBitmap);   // 拷贝图片   Paint iconPaint = new Paint();   iconPaint.setDither(true);// 防抖动   iconPaint.setFilterBitmap(true);// 用来对Bitmap进行滤波处理   Rect src = new Rect(0, 0, iconBitmap.getWidth(), iconBitmap.getHeight());   Rect dst = new Rect(0, 0, iconBitmap.getWidth(), iconBitmap.getHeight());   canvas.drawBitmap(iconBitmap, src, dst, iconPaint);   // 启用抗锯齿和使用设备的文本字距   Paint countPaint = new Paint(Paint.ANTI_ALIAS_FLAG     | Paint.DEV_KERN_TEXT_FLAG);   countPaint.setColor(Color.RED);   canvas.drawCircle(iconSize - 13, 20, 10, countPaint);   Paint textPaint = new Paint();   textPaint.setColor(Color.WHITE);   // textPaint.setTypeface(Typeface.DEFAULT_BOLD);   textPaint.setTextSize(19f);   canvas.drawText(String.valueOf(news), iconSize - 18, 27, textPaint);   return new BitmapDrawable(iconBitmap);  }