通过创建ListView控件并利用适配器将数据传入ListView以达到目标效果，使用ViewHolder对运行效率进行优化并添点击item产生的交互作用，增强实用性。
ListView
效果：
1. 添加ListView控件
1
2
3
4
| <ListView
android:id="@+id/list_view"
android:layout_width="match_parent"
android:layout_height="match_parent" />
|
2. 创建自定义ListView中每一item的布局
fruit_layout.xml
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
| <?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/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" />
</LinearLayout>
|
3. 创建数据源，封装数据
例如创建Fruit.java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
| 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;
}
}
|
使刚才创建的ListView布局中的数据与此类的对象一一对应
4. 创建自定义适配器
数据适配器建立了数据源与ListView之间的适配关系，将数据源转换为ListView能够显示的数据格式，从而将数据的来源与数据的显示进行解耦，降低程序的耦合性。
通常使用BaseAdapter，ArrayAdapter，SimpleAdapter三种适配器其一
这里用ArrayAdapter作为例子
创建FruitAdapter类作为ArrayAdapter的子类
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
| public class FruitAdapter extends ArrayAdapter<Fruit> {
private int resourceId;
public FruitAdapter(Context context, int textViewResourceId,
List<Fruit> objects) {
super(context, textViewResourceId, objects);
resourceId = textViewResourceId;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
Fruit fruit = getItem(position);
View view;
ViewHolder viewHolder;
if(convertView == null) {
view = LayoutInflater.from(getContext()).inflate(resourceId, parent,
false);
viewHolder = new ViewHolder();
viewHolder.fruitImage = (ImageView) view.findViewById(R.id.fruit_image);
viewHolder.fruitName = (TextView) view.findViewById(R.id.fruit_name);
view.setTag(viewHolder);
}else {
view = convertView;
viewHolder = (ViewHolder) view.getTag();
}
viewHolder.fruitImage.setImageResource(fruit.getImageId());
viewHolder.fruitName.setText(fruit.getName());
return view;
}
class ViewHolder{
ImageView fruitImage;
TextView fruitName;
}
}
|
先重写构造函数，将ListView布局id保存：
1
2
3
4
5
6
| private int resourceId;
public FruitAdapter(Context context, int textViewResourceId,
List<Fruit> objects) {
super(context, textViewResourceId, objects);
resourceId = textViewResourceId;
}
|
重写getView()方法，这个方法在每个子项被滚动到屏幕内的时候会被调用
1
2
3
| Fruit fruit = getItem(position);
view = LayoutInflater.from(getContext()).inflate(resourceId, parent,false);
|
使用ListView的缓存机制convertView和viewHolder优化加载过程（被称为“文艺式”）：
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
| public View getView(int position, View convertView, ViewGroup parent) {
Fruit fruit = getItem(position);
View view;
ViewHolder viewHolder;
if(convertView == null) {
view = LayoutInflater.from(getContext()).inflate(resourceId, parent,
false);
viewHolder = new ViewHolder();
viewHolder.fruitImage = (ImageView) view.findViewById(R.id.fruit_image);
viewHolder.fruitName = (TextView) view.findViewById(R.id.fruit_name);
view.setTag(viewHolder);
}else {
view = convertView;
viewHolder = (ViewHolder) view.getTag();
}
viewHolder.fruitImage.setImageResource(fruit.getImageId());
viewHolder.fruitName.setText(fruit.getName());
return view;
}
class ViewHolder{
ImageView fruitImage;
TextView fruitName;
}
|
如果检测到没有缓存，则将资源缓存到viewHolder中，并存入view中。有缓存时则直接调用viewHolder。
5. 在MainActivity中调用适配器
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
| 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();
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();
}
});
}
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);
fruitList.add(banana);
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);
}
}
}
|
将ListView中用到的数据用自定义的init方法逐个添加到数组中，然后将上下文、布局、数组用于创建的适配器对象中。
布局的样式也可以调用系统自带的一些样式:
1
2
3
4
5
6
7
8
9
| simple_list_item1//单独的一行文本框
simple_list_item2//有两个文本框组成
simple_list_item_checked//每项都是由一个已选中的列表项
simple_list_item_multiple_choice//都带有一个复选框
simple_list_item_single_choice//都带有一个单选框
|
然后调用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。
最后用setOnItemClickListener()对ListView注册监听器，当点击item时会回调onItemClick，position中有记录点击的哪一个item，然后进行相应操作。
效果：
