懒加载

public boolean isCreate;
public boolean isVisible;

//mian里
if (isCreate && isVisible) {
lazyData();
}
//声明方法
private void lazyData() {

}
//结尾
   @Override
public void setUserVisibleHint(boolean isVisibleToUser) {
    super.setUserVisibleHint(isVisibleToUser);
    this.isVisible = isVisibleToUser;
    if (isVisibleToUser) {
        if (isCreate && isVisible) {
            lazyData();
        }
    }
}

//预加载
viewPager.setOffscreenPageLimit(3);