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());
}
}
});