UI控件之ListView

一，一个简单的TextView列表

public class FirstActivity extends Activity {
    private String[] data = {"Apple", "Banana", "Orange", "Watermelon",
            "Pear", "Grape", "Pineapple", "Strawberry", "Cherry", "Mango","Apple", "Banana", "Orange", "Watermelon","Pear", "Grape", "Pineapple", "Strawberry", "Cherry", "Mango"};

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.first_layout);
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(         //ArrayAdapter数组适配器
                FirstActivity.this, android.R.layout.simple_list_item_1, data);
      //第一个参数，上下文对象；第二个参数，一个官方的内置布局的id（这是一个TexView）;第三个参数，传入的数据
        ListView listView = (ListView) findViewById(R.id.ListView);
        listView.setAdapter(adapter);
    }
}

二，好玩的东西怎么可以只有Text View呢（来点复杂的）

1.新建一个用于存放水果的类

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

    //构造器初始化
    public Fruit(String name, int imageId) {
        this.name = name;
        this.imageId = imageId;
    }

    public String getName() {
        return name;
    }

    public int getImageId() {
        return imageId;
    }
}

2.新建一个自定义的布局文件

用于描述布局方式，等待被调用

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal">

    <ImageView
        android:id="@+id/fruit_image"
        android:layout_width="50dp"
        android:layout_height="50dp" />

    <TextView
        android:id="@+id/fruit_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</LinearLayout>

3.自定义适配器，继承于ArrayAdapter，并重写getView方法

public class FruitAdapter extends ArrayAdapter<Fruit> {      //泛型指定为Fruit类，就像String也是一个类
    private int resourceId;
    //新建FruitAdapter（）方法，参数一：上下文对象；参数二：布局文件的ID；参数三：传入的数据
    public FruitAdapter(Context context, int textViewResourceId, List<Fruit> objects){
        super(context,textViewResourceId,objects);
        resourceId = textViewResourceId;
    }

    @NonNull
    @Override
    //重写getView() 方法，这个方法在内容被加载之前会执行
    public View getView(int position, View convertView, ViewGroup parent) {
        Fruit fruit = getItem(position);//得到方法传入的Fruit实例
        View view = LayoutInflater.from(getContext()).inflate(resourceId,null);//把构造器获取的id值传入view

        /*ListView的赋值*/
        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;
    }
}

注：在setText的时候不能用int类型数据。

4.在Activity引用的layout中添加<ListView>

    <ListView
        android:id="@+id/ListView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

    </ListView>

5.在Activity中初始化数据并引用ListView

public class FirstActivity extends Activity {
    private List<Fruit> fruitList = new ArrayList<Fruit>();         //创建数组适配器的对象fruitList，范型为<Fruit类>
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.first_layout);
        initFruits();                                           //调用数据初始化函数
        FruitAdapter adapter = new FruitAdapter(FirstActivity.this,R.layout.fruit_item,fruitList);
        //对应的三个参数，上下文，id，适配器数据

        /*对ListView设置自定义适配器的值*/
        ListView listView = (ListView) findViewById(R.id.ListView);
        listView.setAdapter(adapter);
    }

    /*列表参数的值的传入和列表的添加*/
    private void initFruits(){
        Fruit apple = new Fruit("Apple",R.drawable.apple);
        fruitList.add(apple);//一定记得要把对象添加进列表中
        Fruit banana = new Fruit("banana",R.drawable.banane);
        fruitList.add(banana);
        Fruit grape = new Fruit("grape",R.drawable.grape);
        fruitList.add(grape);
        Fruit pear = new Fruit("pear",R.drawable.pear);
        fruitList.add(pear);
        Fruit watermelon = new Fruit("watermelon",R.drawable.watermelon);
        fruitList.add(watermelon);
        Fruit orange = new Fruit("orange",R.drawable.orange);
        fruitList.add(orange);
    }
}

二，ListView之优化

1：控件重用，减少重复加载

public View getView(int position, View convertView, ViewGroup parent) {
        Music music = getItem(position);
        View view;
        if (convertView == null) {
            //对应getView中的参数coverView,一个加载缓存布局的参数。如果没有加载好的布局，则使用LayoutInflater进行布局加载
            view = LayoutInflater.from(getContext()).inflate(ResourceId, null);
        }else {
            view = convertView;//存在布局，则重载布局
        }

2：虽然解决了加载次数，但仍旧每次加载都findViewById

ViewHolder在As加载中出现问题，暂未解决，后续更新优化问题，再研究研究。

三，添加点击事件，为ListView 添加setOnItemClickListener

listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                MainList APP = mainList.get(position);//确定点击位置，返回值为点击类的的对象
                if (APP.getImageId() == R.drawable.list_view_icon) {
                    Intent intent = new Intent(MainActivity.this,MyListView.class);
                    startActivity(intent);
                }
            }
        });