问通知图标在Nougat中显示为正方形

EN

Uri defaultSoundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
            NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this)
                    .setSmallIcon(R.mipmap.app_icon)
                    .setColor(ContextCompat.getColor(getApplicationContext(),R.color.white))
                    .setContentTitle(strTitle)
                    .setContentText(messageBody)
                    .setAutoCancel(true)
                    .setSound(defaultSoundUri)
                    .setContentIntent(pendingIntent);

            NotificationManager notificationManager =
                    (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

            notificationManager.notify(++NOTIFICATION_ID /* ID of notification */, notificationBuilder.build());