ListView

Android 第一行程式碼 第二版 第三章ListView
- activity_main.xml檔案中寫入listView

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent"
 
>

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

    </ListView>
</LinearLayout>

• 定義一個實體類Fruit

public class Fruit {
    private String name;    //水果名稱
    private int imageId;    //影象id

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

    public String getName() {

        return name;
    }

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

• 指定子項的自定義佈局fruit_item

<?xml version="1.0" encoding="utf-8"?>
 

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

    <ImageView
        android:id="@+id/image"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
    <TextView
        android:id="@+id/text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:layout_marginLeft="10dp"/>
    <!--文字水平方向上居中顯示，距離左側10dp-->
</LinearLayout>

• 自定義介面卡FruitAdapter繼承自ArrayAdapter
  
  1. 重寫建構函式，分別傳遞上下文，子項佈局id和資料
  2. 重寫getView()方法
  3. 利用convertView來提升執行效率
  4. 建立ViewHolder類，優化findViewByID()
  5. 利用getTag(),setTag()儲存ViewHolder

public class FruitAdapter extends ArrayAdapter<Fruit> {

    private int resourceId;
    //1.建構函式重寫
    public FruitAdapter(Context context, int resource, List<Fruit> objects) {
        super(context, resource, objects);
        //上下文，子項佈局id，資料
        resourceId = resource;
    }

    //ctrl + O重寫getView方法，每個子項被滾動到螢幕內呼叫
    //position第幾個子項,convertView將之前載入好的佈局進行快取
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        View view;
        Fruit fruit = getItem(position);    // 獲取到當前Fruit例項
        ViewHolder viewHolder;
        //優化listView的執行效率
        if(convertView !=null){
            view = convertView;
            viewHolder = (ViewHolder) view.getTag();
        } else {
            //resourceId將要載入的layout佈局檔案；parent層次結構的父類;false標準寫法
            view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);
            viewHolder = new ViewHolder();
            viewHolder.imageView = (ImageView) view.findViewById(R.id.image);
            viewHolder.textView = (TextView) view.findViewById(R.id.text);
            view.setTag(viewHolder);    //將viewHolder儲存到view中
        }

        viewHolder.imageView.setImageResource(fruit.getImageId());     //設定image影象
        viewHolder.textView.setText(fruit.getName());

        return view;
    }
    class ViewHolder{
        ImageView imageView;
        TextView textView;
    }
}

• 修改MainActivity中的方法
  
  1. 初始化adapter
  2. 獲取listView
  3. 裝載adapter
  4. 設定item點選事件

public class MainActivity extends AppCompatActivity {

    private List<Fruit> fruitList = new ArrayList<>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        //隱藏標題欄
        ActionBar actionBar = getSupportActionBar();
        if(actionBar!=null) {
            actionBar.hide();
        }
        initFruit();    // 初始化fruitList
        //1.初始化adpater
        FruitAdapter fruitAdapter = new FruitAdapter(MainActivity.this,R.layout.fruit_item,
                fruitList);
        //2.獲取listView
        ListView listView = (ListView) findViewById(R.id.list_view);
        //3.裝載adapter
        listView.setAdapter(fruitAdapter);
        //設定item項點選事件
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Fruit fruit = fruitList.get(position);
                Toast.makeText(MainActivity.this,fruit.getName(),Toast.LENGTH_LONG).show();
            }
        });
    }

    private void initFruit() {
        //利用迴圈將資料傳入2次，以實現ListView將螢幕充滿
        for( int i = 0 ; i < 2 ; i++){
            Fruit apple = new Fruit("apple",R.drawable.apple_pic);  //利用建構函式定義apple物件
            fruitList.add(apple);   //裝載apple到fruitList
            Fruit banana = new Fruit("banana",R.drawable.banana_pic);
            fruitList.add(banana);
            Fruit cherry = new Fruit("cherry",R.drawable.cherry_pic);
            fruitList.add(cherry);
            Fruit grape = new Fruit("grape",R.drawable.grape_pic);
            fruitList.add(grape);
            Fruit mango = new Fruit("mango",R.drawable.mango_pic);
            fruitList.add(mango);
            Fruit orange = new Fruit("orange",R.drawable.orange_pic);
            fruitList.add(orange);
            Fruit pear = new Fruit("pear",R.drawable.pear_pic);
            fruitList.add(pear);
            Fruit pineapple = new Fruit("pineapple",R.drawable.pineapple_pic);
            fruitList.add(pineapple);
            Fruit strawberry = new Fruit("strawberry",R.drawable.strawberry_pic);
            fruitList.add(strawberry);
            Fruit watermelon = new Fruit("watermelon",R.drawable.watermelon_pic);
            fruitList.add(watermelon);
        }
    }
}