fragment是怎么和activity绑定的？

问题遇到的现象和发生背景

阅读（开源阅读）源码时产生的疑问

问题相关代码

在开源阅读的MainActivity::createTabFragments()方法中，创建了两个自定义Fragment

protected List<Fragment> createTabFragments() {
       ......
        if (bookListFragment == null)
            bookListFragment = new BookListFragment();
        if (findBookFragment == null)
            findBookFragment = new FindBookFragment();
        return Arrays.asList(bookListFragment, findBookFragment);
    }

但是并未显式地传入activity，那么Fragment是怎么和Activity绑定的？
之后的布局函数

private void setUpTabLayout() {
        mFragmentList = createTabFragments();
        mTitleList = createTabTitles();
        checkParamsIsRight();
        tabFragmentPageAdapter = new TabFragmentPageAdapter(getSupportFragmentManager());
        mVp.setAdapter(tabFragmentPageAdapter);
        mVp.setOffscreenPageLimit(3);
        mTlIndicator.setupWithViewPager(mVp);
    }

肯定是 TabFragmentPageAdapter 里做的操作啊