最常用和最难用的控件——ListView

ListView允许用户通过手指上下滑动的方式将屏幕外的数据滚动到屏幕内，同时屏幕上原有的数据也会滚动出屏幕

新建ListViewTest项目 

在activity_main.xml中添加如下代码定义ViewList控件

<ListView

android:id="@+id/list_view"

android:layout_width="match_parent"

android:layout_height="match_parent">

</ListView>

修改MainActivity中代码如下

public class MainActivity extends Activity {

private String[] data = {"Apple", "Banana", "Orange", "Watermelon",

"Pear", "Grape", "Pineapple", "Strawberry", "Cherry",

"Apple", "Banana", "Orange", "Watermelon",

"Pear", "Grape", "Pineapple", "Strawberry", "Cherry"};

@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);

ListView listView = (ListView) findViewById(R.id.list_view);

listView.setAdapter(adapter);

}

}

3.5.2 定制ListView的界面

首先准备好一组图片分别对应每一种水果

接着定义一个实体类 作为L istView适配器 新建类Fruit代码如下

package com.example.listviewtest;

/**

* Created by 孙伟 on 2016/3/18.

*/

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;

}

}

Fruit类中只有两个字符 name表示水果名字，imageId表示水果对应图片的资源id

<?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>

接下来创建一个自定义的适配器 这个适配器继承自ArrayAdapter 并将泛型指定为Fruit类。新建类FruitAdapter

package com.example.listviewtest;

import android.content.Context;

import android.view.LayoutInflater;

import android.view.View;

import android.view.ViewGroup;

import android.widget.ArrayAdapter;

import android.widget.ImageView;

import android.widget.TextView;

import java.util.List;

/**

* Created by 孙伟 on 2016/3/18.

*/

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);//获取当前项的Fruit实例

View view;

if (convertView == null) {

view = LayoutInflater.from(getContext()).inflate(resourceId,null);

} 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;

}

}

最后在MainActivity中修改为

package com.example.listviewtest;

import android.app.Activity;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.widget.ArrayAdapter;

import android.widget.ListView;

import java.util.ArrayList;

import java.util.List;

public class MainActivity extends Activity {

private List<Fruit> fruitList = new ArrayList<Fruit>();

@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_activity,fruitList);

ListView listView = (ListView) findViewById(R.id.list_view);

listView.setAdapter(adapter);

}

private void initFruits() {

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);

}

}

3.5.3 提升ListView效率