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

创建一个class，代表你每一行想放的东东

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

New一个ArrayList，用来储存你想放的东东们

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

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

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

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：