1 簡單使用ListView:
在布局文件中添加ListView控件
通過適配器將數(shù)據(jù)傳遞給ListView:
private String[] data={"zhangsan","lisi","wangwu","dengdeng"};
ArrayAdapter adapter=new ArrayAdapter (MainActivity.this,
android.R.layout.simple_list_item_1, data);
ListView listView=(ListView)findViewById(R.id.list_view);
listView.setAdapter(adapter);
其中android.R.layout.simple_list_item_1是為ListView指定的子項布局的id
2 定制ListView界面
通俗的說：將兩種原料（容器中裝的數(shù)據(jù)集和ListView的子項的布局文件）在加工器（適配器Adapter）的加工下一一匹配（布局文件中控件要顯示的內(nèi)容和數(shù)據(jù)集中的各個數(shù)據(jù)項一一對應(yīng)）澜薄。
本例中是將水果和對應(yīng)的名稱作為數(shù)據(jù)顯示在ListView中
2.1 數(shù)據(jù)集
自定義一個類暖侨，將要顯示的數(shù)據(jù)作為對象屬性封裝在類中
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;
}
}
2.2 子項布局文件
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal"
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_margin="10dp"/>
</LinearLayout>
2.3 自定義適配器
public class FruitAdapter extends ArrayAdapter<Fruit> {
private int resourceId;
public FruitAdapter(Context context, int resource, List<Fruit> objects) {
super(context, resource, objects);
resourceId=resource;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
Fruit fruit=getItem(position);
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;
}
}
2.4 為ListView設(shè)定適配器柜砾，顯示數(shù)據(jù)
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);
}
private void initFruits(){
for(int i=0;i<4;i++) {
Fruit apple = new Fruit("蘋果", R.drawable.apple);
fruitList.add(apple);
Fruit caomei = new Fruit("草莓", R.drawable.caomei);
fruitList.add(caomei);
Fruit migua = new Fruit("蜜瓜", R.drawable.migua);
fruitList.add(migua);
Fruit orange = new Fruit("橘子", R.drawable.orange);
fruitList.add(orange);
Fruit putao = new Fruit("葡萄", R.drawable.putao);
fruitList.add(putao);
Fruit qiyiguo = new Fruit("奇異果", R.drawable.qiyiguo);
fruitList.add(qiyiguo);
}
}
}
3 優(yōu)化，提升ListView效率
- 為避免快速滑動時重復(fù)加載布局重新加載，注意到自定義的適配器中g(shù)etView()方法中有一個參數(shù)convertView唬渗，這個參數(shù)用于將之前加載好的布局進行緩存堰酿，以便之后可以進行重用良狈，所以修改FruitAdapter中的代碼如下：
@Override
public View getView(int position, View convertView, ViewGroup parent) {
Fruit fruit=getItem(position);
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;
}
可以看到徒像，現(xiàn)在我們在getView()方法中進行了判斷黍特，如果convertView為null，則使用Layout工nflater去加載布局锯蛀，如果不為null則直接對convertView進行重用灭衷。這樣就大大提高了ListView的運行效率，在快速滾動的時候也可以表現(xiàn)出更好的性能旁涤。
- 不過翔曲，目前我們的這份代碼還是可以繼續(xù)優(yōu)化的，雖然現(xiàn)在已經(jīng)不會再重復(fù)去加載布局劈愚，但是每次在getView()方法中還是會調(diào)用View的findViewById()方法來獲取一次控件的實例瞳遍，我們可以借助一個ViewHolder來對這部分性能進行優(yōu)化，修改FruitAdapter中的代碼菌羽，如下所示:
@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);//將viewHolder存儲在view中
}
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;
}
我們新增了一個內(nèi)部類ViewHolder掠械，用于對控件的實例進行緩存。當(dāng)convertView為null 的時候注祖，創(chuàng)建一個ViewHolder對象猾蒂，并將控件的實例都存放在ViewHolder里，然后調(diào)用View 的setTag()方法是晨，將ViewHolder對象存儲在View中肚菠。當(dāng)convertView不為null的時候，
則調(diào)用View的getTag()方法罩缴，把ViewHolder重新取出案糙。這樣所有控件的實例都緩存在了 ViewHolder里，就沒有必要每次都通過findViewBy工do方法來獲取控件實例了靴庆。
通過這兩步優(yōu)化之后时捌，我們ListView的運行效率就已經(jīng)非常不錯了。
4 ListView的點擊事件
- 為ListView設(shè)置子項監(jiān)聽器炉抒，修改代碼如下：
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);
ActionBar actionBar=getSupportActionBar();
if(actionBar!=null){
actionBar.hide();
}
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<10;i++) {
Fruit apple = new Fruit("蘋果", R.drawable.apple);
fruitList.add(apple);
Fruit caomei = new Fruit("草莓", R.drawable.caomei);
fruitList.add(caomei);
Fruit migua = new Fruit("蜜瓜", R.drawable.migua);
fruitList.add(migua);
Fruit orange = new Fruit("橘子", R.drawable.orange);
fruitList.add(orange);
Fruit putao = new Fruit("葡萄", R.drawable.putao);
fruitList.add(putao);
Fruit qiyiguo = new Fruit("奇異果", R.drawable.qiyiguo);
fruitList.add(qiyiguo);
}
}
}
