第一行代码笔记之——ListView

1.ListView 是啥

ListView  就是一个能显示一排一排的东西View控件

 

2.使用ListView的步骤

1. 创建一个class，代表你每一行想放的东东
2. 给你每一行的东东一个布局文件，在activity的布局文件中加一个ListView  控件
3. New一个ArrayList，用来储存你想放的东东们
4. 在Activity中写一个初始化函数init()，初始化东东，然后把东东add到ArrayList中
5. 如果是创建复杂控件，要建一个继承于ArrayAdapter的类，再到里面添加复杂功能
6. New一个你的ArrayAdapter，把每一行的那个xml文件和已初始化完毕的ArrayList给它
7. New一个ListView  ，并findViewById，把ArrayAdapter给它。

 

3.最简单的ListView

     1.在XML文件中添加一个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>

      2.

          （1）在MainActivity中用一个Sting[]储存每行数据

          （2）把数据给ArrayAdapter

          （3）把ArrayAdapter给ListView 

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

    }

 

效果图：

 

 

4.ListView的事件监听器

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();

            }

        });

 

5.复杂的ListView

1.新建一个Fruit类

   作用：帮助我们储存与获得“水果名称”，与“图片ID”

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.新建一个XML文件

   作用：来作为每行内容的布局文件

<?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>

 

3.初始化数据

    步骤：

           ①new一个ArrayList<Fruit>

           ②在MainActivity中写一个函数init()。

 

    作用：初始化数据，并将数据add到ArrayList<Fruit>中

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);

    }

 

4.新建一个继承于ArrayAdapter<Fruit>的FruitAdapter类

   作用：用来设定水果名称与水果图片

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;

    }

}

 

5把R.layout.fruit_item和初始化完毕的ArrayList<Fruit>给FruitAdapter，然后把FruitAdapter给ListView

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);

    }

}

 

效果图：