[android笔记]ListView的简单使用

ListView是android中最常用的控件之一,几乎所有的应用程序都会用它. ListView允许用户通过手指上下滑动的方式将屏幕外的数据滚动到屏幕内,同时屏幕上原有的数据会滚动出屏幕外,比如手机联系人、微博等.

定制ListView界面

定义实体类Fruit作为ListView的适配器类型。

public class Fruit {
    private String name;
    private int imageId;

    public Fruit(String name,int imageId) {
        this.name = name;
        this.imageId = imageId;
    }



    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getImageId() {
        return imageId;
    }

    public void setImageId(int imageId) {
        this.imageId = imageId;
    }
}

然后为ListView的子项新建一个我们自定义的布局，在layout下新建fruit_item.xml文件，如下：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.test.l.MainActivity">

    <ImageView
        android:id="@+id/fruit_image"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
    <TextView
        android:id="@+id/fruit_name"
        android:layout_gravity="center"
        android:layout_marginLeft="10dip"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
LinearLayout>

上述布局中ImageView用于显示水果的图片，TextView用于显示水果的名称。

接下来创建自定义的适配器，这个适配器FruitAdapter继承自ArrayAdapter，并将泛型指定为我们定义的Fruit类，如下：

public class FruitAdapter extends ArrayAdapter<Fruit> {
    private  int resourceId;
    public FruitAdapter(Context context, int textViewResourceId, List objects){
        super(context,textViewResourceId,objects);
        resourceId =textViewResourceId;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        Fruit fruit = getItem(position);
        View view = LayoutInflater.from(getContext()).inflate(resourceId,null);
        ImageView fruitImage= (ImageView)view.findViewById(R.id.fruit_image);
        TextView fruitName = (TextView)view.findViewById(R.id.fruit_name);
        fruitImage.setImageResource(fruit.getImageId());
        fruitName.setText(fruit.getName());
        return view;
    }
}

FruitAdapter重写了父类的构造方法，又重写了getView方法，该方法在每个子项被滚动到屏幕内的时候会被调用，该方法中首先通过getItem方法得到当前的Fruit实例，然后使用LayoutInflater来为这个子项加载我们传入的布局，然后就是获得ImageView和TextView的实例，分别用于显示水果图片和名称。

然后就是MainActivity的修改，如下：

public class MainActivity extends AppCompatActivity {

    private List fruits = new ArrayList();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        initfruits();
        FruitAdapter adapter = new FruitAdapter(MainActivity.this,R.layout.fruit_item,fruits);

        ListView listView = (ListView)findViewById(R.id.list_view);
        listView.setAdapter(adapter);
    }

    private  void initfruits(){
        Fruit apple = new Fruit("苹果",R.mipmap.ic_launcher);
        fruits.add(apple);

        Fruit banana = new Fruit("香蕉",R.mipmap.ic_launcher);
        fruits.add(banana);

        Fruit taozi = new Fruit("桃子",R.mipmap.ic_launcher);
        fruits.add(taozi);

        Fruit putao = new Fruit("葡萄",R.mipmap.ic_launcher);
        fruits.add(putao);

        Fruit chengzi = new Fruit("橙子",R.mipmap.ic_launcher);
        fruits.add(chengzi);

        Fruit boluo = new Fruit("菠萝",R.mipmap.ic_launcher);
        fruits.add(boluo);

        Fruit pingguo = new Fruit("苹果",R.mipmap.ic_launcher);
        fruits.add(pingguo);

        Fruit caomei = new Fruit("草莓",R.mipmap.ic_launcher);
        fruits.add(caomei);
    }
}

这里添加的initFruits方法用于初始化水果数据。最后运行效果如下：

ListView的点击事件

ListView如何响应用户的点击事件？

public class MainActivity extends AppCompatActivity {

    private List fruits = new ArrayList();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        initfruits();
        FruitAdapter adapter = new FruitAdapter(MainActivity.this,R.layout.fruit_item,fruits);

        ListView listView = (ListView)findViewById(R.id.list_view);
        listView.setAdapter(adapter);
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView parent, View view, int position, long id) {
                Fruit fruit = fruits.get(position);
                Toast.makeText(MainActivity.this,fruit.getName(),Toast.LENGTH_SHORT).show();
            }
        });
    }

    private  void initfruits(){
        Fruit apple = new Fruit("苹果",R.mipmap.ic_launcher);
        fruits.add(apple);

        Fruit banana = new Fruit("香蕉",R.mipmap.ic_launcher);
        fruits.add(banana);

        Fruit taozi = new Fruit("桃子",R.mipmap.ic_launcher);
        fruits.add(taozi);

        Fruit putao = new Fruit("葡萄",R.mipmap.ic_launcher);
        fruits.add(putao);

        Fruit chengzi = new Fruit("橙子",R.mipmap.ic_launcher);
        fruits.add(chengzi);

        Fruit boluo = new Fruit("菠萝",R.mipmap.ic_launcher);
        fruits.add(boluo);

        Fruit pingguo = new Fruit("苹果",R.mipmap.ic_launcher);
        fruits.add(pingguo);

        Fruit caomei = new Fruit("草莓",R.mipmap.ic_launcher);
        fruits.add(caomei);
    }
}

这里使用了setOnItemClickListener方法为ListView注册了一个监听器，用户点击了ListView的任何一项时就会调用onItemClick方法在该方法中可以通过position参数来判断是点击了哪一项。