第一行代码札记之——ListView

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"    android:paddingRight="@dimen/activity_horizontal_margin"    android:paddingTop="@dimen/activity_vertical_margin"    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">    <ListView        android:id="@+id/list_view"        android:layout_width="match_parent"        android:layout_height="match_parent"/></RelativeLayout>

public class MainActivity extends Activity {    private String[] data={"Apple","Banana","Orange","Watermelon","Pear","Grape","Pineapple","Strawberry","Cherry","Mango"};//要储存的数据    @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);//把每一行内容的XML文件与数据给ArrayAdapter        ListView listView=(ListView)findViewById(R.id.list_view);        listView.setAdapter(adapter);//把ArrayAdapter给ListView    }

listView.setOnItemClickListener(new OnItemClickListener() {            @Override            public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) {                Fruit fruit=fruitList.get(position);                Toast.makeText(MainActivity.this,fruit.getName(),Toast.LENGTH_LONG).show();            }        });

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;    }}

<?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"        android:layout_marginLeft="10dip"/></LinearLayout>

public class MainActivity extends Activity {    private List<Fruit> fruitList=new ArrayList<Fruit>();//①new一个ArrayList<Fruit>    @Override    protected void onCreate(Bundle savedInstanceState)     {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        init();//初始化数据    }    private void init()    {        Fruit apple=new Fruit("Apple",R.drawable.apple);fruitList.add(apple);//将数据add到ArrayList<Fruit>中        Fruit banana=new Fruit("Banana",R.drawable.banana);fruitList.add(banana);        Fruit orange=new Fruit("Orange",R.drawable.orange);fruitList.add(orange);        Fruit watermelon=new Fruit("Watermelon",R.drawable.watermelon);fruitList.add(watermelon);        Fruit pear=new Fruit("Pear",R.drawable.pear);fruitList.add(pear);        Fruit grape=new Fruit("Grape",R.drawable.grape);fruitList.add(grape);        Fruit pineapple=new Fruit("Pineapple",R.drawable.pineapple);fruitList.add(pineapple);        Fruit strawberry=new Fruit("Strawberry",R.drawable.strawberry);fruitList.add(strawberry);        Fruit cherry=new Fruit("Cherry",R.drawable.cherry);fruitList.add(cherry);        Fruit mango=new Fruit("Mango",R.drawable.mango);fruitList.add(mango);    }

public class FruitAdapter extends ArrayAdapter<Fruit>{    private int resourceId;//等会要把R.layout.fruit_item的值赋给resourceId        class ViewHolder//用来暂存“水果名称”的TextView控件与“水果图片”的ImageView控件，避免每次都重新加载布局，优化程序的流畅度    {        ImageView fruitImage;        TextView fruitName;    }        public FruitAdapter(Context context,int textViewResourceId,List<Fruit> objects)    {        super(context,textViewResourceId,objects);        resourceId=textViewResourceId;//把R.layout.fruit_item的值赋给resourceId    }    public View getView(int position,View convertView,ViewGroup parent)//这个函数不是太清楚，大概是用来createView的，对于每一个添加进ArrayList<Fruit>的Fruit对象，都会执行一边    {        Fruit fruit=getItem(position);//实例化在ArrayList<Fruit>中第“position”个当前Fruit对象        View view;        ViewHolder viewHolder;        if (convertView==null)//如果布局从来没有被加载过        {            view=LayoutInflater.from(getContext()).inflate(resourceId,null);//使用布局填充器来把fruit_item布局文件转为View            viewHolder=new ViewHolder();//新建一个ViewHolder            viewHolder.fruitImage=(ImageView)view.findViewById(R.id.fruit_image);//从View中获取ImageView，并暂存新建的ViewHolder中            viewHolder.fruitName=(TextView)view.findViewById(R.id.fruit_name);//从View中获取TextView，并暂存新建的ViewHolder中            view.setTag(viewHolder);//使用setTag把查找的view缓存起来方便多次重用        }        else//布局被加载过        {            view=convertView;            viewHolder=(ViewHolder)view.getTag();//把之前暂存的ViewHolder赋给viewHolder        }        viewHolder.fruitImage.setImageResource(fruit.getImageId());//设定水果图片        viewHolder.fruitName.setText(fruit.getName());//设定水果名称        return view;    }}

public class MainActivity extends Activity{    private List<Fruit> fruitList=new ArrayList<Fruit>();//①new一个ArrayList<Fruit>    @Override    protected void onCreate(Bundle savedInstanceState)    {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        init();//初始化数据        FruitAdapter adapter=new FruitAdapter(MainActivity.this,R.layout.fruit_item,fruitList);//把R.layout.fruit_item和初始化完毕的ArrayList<Fruit>给FruitAdapter        ListView listView=(ListView)findViewById(R.id.list_view);        listView.setAdapter(adapter);//把FruitAdapter给ListView    }    private void init()    {        Fruit apple=new Fruit("Apple",R.drawable.apple);fruitList.add(apple);//将数据add到ArrayList<Fruit>中        Fruit banana=new Fruit("Banana",R.drawable.banana);fruitList.add(banana);        Fruit orange=new Fruit("Orange",R.drawable.orange);fruitList.add(orange);        Fruit watermelon=new Fruit("Watermelon",R.drawable.watermelon);fruitList.add(watermelon);        Fruit pear=new Fruit("Pear",R.drawable.pear);fruitList.add(pear);        Fruit grape=new Fruit("Grape",R.drawable.grape);fruitList.add(grape);        Fruit pineapple=new Fruit("Pineapple",R.drawable.pineapple);fruitList.add(pineapple);        Fruit strawberry=new Fruit("Strawberry",R.drawable.strawberry);fruitList.add(strawberry);        Fruit cherry=new Fruit("Cherry",R.drawable.cherry);fruitList.add(cherry);        Fruit mango=new Fruit("Mango",R.drawable.mango);fruitList.add(mango);    }}