安卓Textview的getLineCount返回0

ViewTreeObserver observer = tv.getViewTreeObserver(); // textAbstract为TextView控件
            observer.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {  

                @Override
                public void onGlobalLayout() {
                    ViewTreeObserver obs = tv.getViewTreeObserver();
                    obs.removeGlobalOnLayoutListener(this);
                    if (tv.getLineCount() >= 2) {
                        System.out.println("行数" + tv.getLineCount());
                    }
                }
            });