android体系结构组件AndroidViewModel实例无法创建。尝试制作一个简单的Room DB

Question

这里是我的类，在其中扩展AndroidViewModel的地方，试图通过应用程序构造函数获取数据库上下文，但是当我从MainActivity调用它时，抛出了一个错误，说java.lang.RuntimeException：无法创建类的实例com.example.roomdb33.BookViewModel

public class BookViewModel extends AndroidViewModel {

 final BookDAO bookDAO;





public BookViewModel(@NonNull Application application) {
    super(application);
   BookRoomDB bookDB = BookRoomDB.getDatabse(application);
    bookDAO = bookDB.bookDAO();

}



//For Inserting
void insert(BookEntity book){

    InsertAsyncTask insertAsyncTask = new InsertAsyncTask(bookDAO);

    insertAsyncTask.execute(book);
     static class InsertAsyncTask extends AsyncTask<BookEntity,Void,Void>{

    final BookDAO bookDAO;

InsertAsyncTask(BookDAO bookDAO) {
    this.bookDAO = bookDAO;
}

@Override
protected Void doInBackground(BookEntity... bookEntities) {
    bookDAO.insert(bookEntities[0]);
    return null;
     }
   }
  }

我的BookRoomDB有一个getDatabase方法，位于

下

static BookRoomDB getDatabse(Context context){
    if (bookRoomDB == null){
        synchronized (BookRoomDB.class){
            if (bookRoomDB == null){
                bookRoomDB = Room.databaseBuilder(context.getApplicationContext(),BookRoomDB.class,"book_database")
                        .build();
            }
        }
    }

这是我在MainActivity中打电话的方式

 BookViewModel bookViewModel;
 bookViewModel = ViewModelProviders.of(this).get(BookViewModel.class);