Android的ListView使用

2017-12-10 本文已影响0人 Mason_Xu

ListView

ListView 简单用法

width和height是match_parent
数据可以从数据库,网上下载.也可以是数组
数组中的数据是无法直接传递给ListView的,要借助适配器,其中ArrayAdapter最好用
ArrayAdapter可以用泛型指定数据类型,在构造函数中吧要适配的数据传入
ArrayAdapter有多个构造函数重载,要选择最适合的一种.因为传入数据是字符串,所以ArrayAdapter<String>
构造函数传入(上下文,ListView子项布局id,适配数据)

最后调用ListView的setAdapter()方法,将构建好的适配器对象传递进去 ,这样ListView和数据之间的关联就建立完成了

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

public class MainActivity extends AppCompatActivity {

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.activity_main);
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(
            MainActivity.this,android.R.layout.simple_list_item_1,data);
    ListView listView = (ListView) findViewById(R.id.list_view);
    listView.setAdapter(adapter);
   }
}

定制ListView的界面

定义一个实体类,作为ListView适配器的适配类型,新建Fruit

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 int getImageId() {
    return imageId;
}
}

自定义布局 LinearLayout 要 TextVIew垂直布局居中

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

 <TextView
  android:id="@+id/fruit_name"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_gravity="center_vertical"
  android:layout_marginLeft="10dp" />

创建适配器

继承自ArrayAdapter 泛型Fruit 新建类FruitAdapter
Fruit重写一组父类的构造函数,用于将上下文,ListView子项布局的id和数据传递进来
重写getView()方法,这个方法每个子项被滚动到屏幕内的时候会被调用.
在getView()方法中,首先通过getItem()方法得到当前项的Fruit实例,然后使用LayoutInflater 来为这个子项加载传入的布局
inflate()接收三个参数 ()

调用View的findViewById() 获取ImageView和TextView的实例,并分别调用他们的setImageResource()和setText()方法来设置显示的图片和文字,最后布局返回

public class FruitAdapter extends ArrayAdapter {
       private int resourceId;

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

@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
       Fruit fruit = (Fruit) getItem(position); // 获取当前项的Fruit实例
       View view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);
       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;

}
}

initFruit()方法初始化所有水果数据

onCreat() 方法中创建FruitAdapter对象,并将FruitAdapter作为适配器传递给ListVIew,这样定制ListView界面的任务就完成了

public class MainActivity extends AppCompatActivity {

private List<Fruit> fruitList = new ArrayList<>();

 @Override
 protected void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     setContentView(R.layout.activity_main);
     initFruits(); // 初始化水果数据
     FruitAdapter adapter = new FruitAdapter(MainActivity.this,R.layout.fruit_item,fruitList);
     ListView listView = (ListView) findViewById(R.id.list_view);
     listView.setAdapter(adapter);
 }

 private void initFruits() {
     for (int i = 0; i < 2; i++) {
         Fruit apple = new Fruit("Apple", R.drawable.apple_pic);
         fruitList.add(apple);
         Fruit banana = new Fruit("banana", R.drawable.banana_pic);
         Fruit orange = new Fruit("orange", R.drawable.orange_pic);
         fruitList.add(orange);
         Fruit watermelon = new Fruit("watermelon", R.drawable.watermelon_pic);
         fruitList.add(watermelon);
         Fruit pear = new Fruit("pear", R.drawable.pear_pic);
         fruitList.add(pear);
         Fruit grape = new Fruit("grape", R.drawable.grape_pic);
         fruitList.add(grape);
         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 cherry = new Fruit("cherry", R.drawable.cherry_pic);
         fruitList.add(cherry);
         Fruit mango = new Fruit("mango", R.drawable.mango_pic);
         fruitList.add(mango);
     }
 }
}

提升ListView运行效率修改FruitAdapter

在getView() 方法中还有 convertView参数,用于将之前加载好的布局进行缓存,以后可重用

对getView()方法进行判断,如果convertView为null,则使用LayoutInflater 加载布局,不为null则直接对convertView进行重用

public class FruitAdapter extends ArrayAdapter {
  ...
  @Override
  public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
      Fruit fruit = (Fruit) getItem(position); // 获取当前项的Fruit实例
      View view;
      if(convertView == null){
          view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);
      }else{
          view = convertView;
      }
      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;
  }
}

继续优化借助ViewHolder来对部分性能进行优化修改FruitAdapter 📖P120

新建一个内部类ViewHolder,用于对控件的实例进行缓存
当converView为null时,创建一个ViewHolder对象,并将控件的实例都存放在ViewHolder里
然后调用View的setTag() 方法,将ViewHolder对象存储在View中.
当convertView不为null时,则调用View的getTag()方法,吧ViewHolder重新取出.

这样所有空间的实例都缓存在了ViewHolder里,就没有必要每次都通过findViewById() 方法来获取控件实例

public class FruitAdapter extends ArrayAdapter {
  ...
  @Override
  public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
      Fruit fruit = (Fruit) getItem(position); // 获取当前项的Fruit实例
      View view;
      ViewHoler viewHolder;
      if(convertView == null){
          view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);
          viewHolder = new ViewHoler();
          viewHolder.fruitImage = (ImageView)   view.findViewById(R.id.fruit_image);
          viewHolder.fruitName = (TextView) view.findViewById(R.id.fruit_name);
          view.setTag(viewHolder); // 将ViewHolder存储在View中
      }else{
          view = convertView;
          viewHolder = (ViewHoler) view.getTag(); // 重新获取ViewHolder
      }
      viewHolder.fruitImage.setImageResource(fruit.getImageId());
      viewHolder.fruitName.setText(fruit.getName());
      return view;
  }
  class ViewHoler{
      ImageView fruitImage;
      TextView fruitName;
    }
}

为ListView添加点击事件

在MainActivity 添加点击事件 Toast

使用setOnItemClickListener() 方法为ListView 注册一个监听器
点击任何一个子项是,回调onItemClick() 方法
这个方法可以通过position 参数判断用户点击的是哪个子项,然后获取相应的水果

通过Toast将水果的名字显示出来

public class MainActivity extends AppCompatActivity {

  private List<Fruit> fruitList = new ArrayList<>();

  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      initFruits(); // 初始化水果数据
      FruitAdapter adapter = new FruitAdapter(MainActivity.this,R.layout.fruit_item,fruitList);
      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 = fruitList.get(position);
            Toast.makeText(MainActivity.this,fruit.getName(),Toast.LENGTH_SHORT).show();
        }
    });
  }

  ...
}

这是我学习Android的笔记,参考书<<第一行代码-第二版>>,感谢郭霖大神
如有不足之处,可以一起讨论
附上郭霖的blog http://blog.csdn.net/guolin_blog

Android的ListView使用

ListView

ListView 简单用法

定制ListView的界面

提升ListView运行效率修改FruitAdapter

在getView() 方法中还有 convertView参数,用于将之前加载好的布局进行缓存,以后可重用

继续优化借助ViewHolder来对部分性能进行优化修改FruitAdapter 📖P120

为ListView添加点击事件

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Android的ListView使用

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ListView 简单用法

定制ListView的界面

提升ListView运行效率 修改FruitAdapter

在getView() 方法中还有 convertView参数,用于将之前加载好的布局进行缓存,以后可重用

继续优化 借助ViewHolder来对部分性能进行优化 修改FruitAdapter 📖P120

为ListView添加点击事件

猜你喜欢

热点阅读

提升ListView运行效率修改FruitAdapter

继续优化借助ViewHolder来对部分性能进行优化修改FruitAdapter 📖P120