一.适配器Adapter

public class BookAdapter extends BaseAdapter {
    private List<Book> bookList;
    private Context context;
    private LayoutInflater layoutInflater;

    /*
    1.Context是一个场景，作为一个抽象类，Activity，Service，Application是它的子类
    2.两个参数，一个传入数据，一个传入Context
     */
    public BookAdapter(List<Book> bookList, Context context) {
        this.bookList = bookList;
        this.context = context;
        layoutInflater=LayoutInflater.from(context);
    }

    @Override
    public int getCount() {
        return bookList.size();
    }

    @Override
    public Object getItem(int position) {
        return bookList.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if(convertView==null){
            convertView=layoutInflater.inflate(R.layout.item_book,null);
        }
        Holder holder= (Holder) convertView.getTag();
        if (holder==null){
            holder=new Holder();
            holder.bookImg=convertView.findViewById(R.id.bookImg);
            holder.bookNametxt=convertView.findViewById(R.id.bookNametxt);
            holder.authortxt=convertView.findViewById(R.id.authortxt);
            convertView.setTag(holder);
        }
        holder.bookImg.setImageAlpha(bookList.get(position).getPicture());
        holder.bookNametxt.setText("书名："+bookList.get(position).getName());
        holder.authortxt.setText("作者："+bookList.get(position).getAuthor());
        return convertView;
    }

    //起到缓存的效果
    class Holder{
        ImageView bookImg;
        TextView bookNametxt;
        TextView authortxt;
    }

}

二.ListView

public class BookListActivity extends AppCompatActivity {

    private ListView listView;
    private BookAdapter bookAdapter;
    private List<Book> bookList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_book_list);
        initView();
    }

    public void initView(){
        listView=findViewById(R.id.bookList);
        BookDao bookDao=new BookDao();
        bookList=bookDao.findAll();
        //bookDao.addBook();
        bookAdapter=new BookAdapter(bookList,BookListActivity.this);
        listView.setAdapter(bookAdapter);
    }
}