Android ListView 的简单用法

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参考 API 和《第一行代码》

1. ListView is a view group that displays a list of scrollable items. The list items are automatically inserted to the list using an Adapter that pulls content from a source such as an array or database query and converts each item result into a view that’s placed into the list.
2. When the content for your layout is dynamic or not pre-determined, you can use a layout that subclasses AdapterView to populate the layout with views at runtime. A subclass of the AdapterView class uses an Adapter to bind data to its layout. The Adapter behaves as a middleman between the data source and the AdapterView layout—the Adapter retrieves the data (from a source such as an array or a database query) and converts each entry into a view that can be added into the AdapterView layout.

ListView 用来显示一个可以垂直滚动的列表,其中列表的每一项由其相关联的适配器提供,适配器起到一个中间人的作用,即连接列表数据和ListView布局

使用默认 ListView, 先定义一个数组(ArrayList)保存要在ListView里显示的数据,然后新建一个适配器,构造函数传入系统默认的子项目布局( android.R.layout.simple_list_item_1 )–(显示一个 TextView )和数据存在的数组,再直接调用 ListView 的 setAdapter() 方法,传入新建好的适配器,即可显示数据.

使用自定义的 ListView, 可以在子项目中不只显示一个 TextView, 而是可以显示其他自己定义的布局,所以要

1. 先新建一个子项目布局,里面可以添加 TextView, Button, ImageView 等控件;
2. 后新建一个类 Item 与子项目布局里的控件对应,用作 List<\T> 的范型和要继承的 ArrayAdapter<\T> 的范型,也是要显示的数据类型;
3. 自定义 Adapter 类扩展自 ArrayAdapter<\T>, 重写 getView() 方法,先 getItem(position) 获取当前 Item 实例,然后 LayoutInflater.from(getContext()).inflate(resourceId,parent,false) 获取子项目布局 View 实例,再通过 View.findViewById() 获取子项目布局里的控件实例,最后调用 setText() 等控件方法完成控件的操作,返回 View.
4. 然后和使用默认 ListView 一样,新建一个自定义的适配器,传入自定义的子项目布局和要显示的数据,再直接调用 ListView 的 setAdapter() 方法,传入新建好的适配器,即可显示数据.
5. 要增加新的数据,只需要调用 Adapter.add(Item) 即可.

例 :

public class Item { 
   
    private String text;
    private int button;
    
    public Item(String text,int button){ 
   
        this.text=text;
        this.button=button;
    }
    public String getText(){ 
   
        return text;
    }
    public int getButton(){ 
   
        return button;
    }
}

public class ItemAdapter extends ArrayAdapter<Item> { 
   
    private int resourceId;
    public ItemAdapter(Context context,int resource,List<Item> data){ 
   
        super(context,resource,data);
        resourceId=resource;
    }
    @Override
    public View getView(int position, View convertView, ViewGroup parent){ 
   
        final Item item=getItem(position);
        View view;
        ViewHolder holder=new ViewHolder();  // viewHolder 是提升 ListView 运行效率
        if(convertView==null){ 
   
            view = LayoutInflater.from(getContext()).inflate(resourceId,parent,false);
            holder.tv=view.findViewById(R.id.text_view);
            holder.bn=view.findViewById(R.id.button);
            view.setTag(holder);
        } else { 
   
            view = convertView;
            holder=(ViewHolder) view.getTag();
        }
        holder.tv.setText(item.getText());
        holder.bn.setOnClickListener(new View.OnClickListener() { 
   
            @Override
            public void onClick(View v) { 
   
                Toast.makeText(getContext(),"you clicked button"+item.getButton(),Toast.LENGTH_SHORT).show();
            }
        });
        return view;
    }
    class ViewHolder{ 
   
        TextView tv;
        Button bn;
    }
}

public class MainActivity extends AppCompatActivity { 
   

    private ArrayList<Item> data=new ArrayList<>();
    @Override
    protected void onCreate(Bundle savedInstanceState) { 
   
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initData();
        ItemAdapter adapter=new ItemAdapter(this,R.layout.list_view_item,data);
        ListView listView=(ListView) findViewById(R.id.list_view);
        listView.setAdapter(adapter);
    }

    private void initData(){ 
   
        for(int i=0;i<20;++i){ 
   
            Item a=new Item("list view test. no "+i,i);
            data.add(a);
        }
    }
}

运行效果 :