UnderlinePageIndicator.java 文件源码

@Override
public void setViewPager(ViewPager viewPager) {
    if (mViewPager == viewPager) {
        return;
    }
    if (mViewPager != null) {
        //Clear us from the old pager.
        mViewPager.setOnPageChangeListener(null);
    }
    if (viewPager.getAdapter() == null) {
        throw new IllegalStateException("ViewPager does not have adapter instance.");
    }
    mViewPager = viewPager;
    mViewPager.setOnPageChangeListener(this);
    invalidate();
    post(new Runnable() {
        @Override public void run() {
            if (mFades) {
                post(mFadeRunnable);
            }
        }
    });
}