今天犯了一个简单的错：
List<Book> books = adapter.data;
for(Book book: books){
if(book.id == bookId){
books.remove(book);
}
}
结果遇到java.util.ConcurrentModificationException,起初以为是Android里操作不在同一线程的UI的问题，其实没那么复杂，只是犯了一个常见的Java错误。改为下面即可：
List<Book> books = .;
Book deletedBook = ;
(Book book: books){
(book.== bookId){
deletedBook = book;
;
}
}
books.remove(deletedBook);