ListView日常笔记

一.listView的简单用法
二.自定义适配器
三.listView的优化

1.listView的简单用法

在布局文件中加入listView空间,代码如下:

<ListView
android:id="@+id/list_view"
android:layout_width="match_parent"
android:layout_height="match_parent">

</ListView>

MainActivity中的代码

protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//数组中的数据是无法直接传递给ListView的，需要记住适配器来完成
//一个参数为上下文context对象,第一个参数是listview的子布局Id,这里我们使用的是内置的布局文件,
//可用于显示简单的文字,第三个参数是数据
ArrayAdapter<String> adapter = new ArrayAdapter<String>(MainActivity.this,
android.R.layout.simple_list_item_1, data);

ListView listView = (ListView) findViewById(R.id.list_view);
//将构建好的适配器对象传递进去,listview和数据之间的关联就建立好了
listView.setAdapter(adapter);

}

2.自定义适配器，定制listView的界面

1.定义一个实体类

package com.caobo.listviewtest;
public class Fruit {
private String name;
private int imageId;

public Fruit(String name, int imageId) {
this.name = name;
this.imageId = imageId;
}

public Str
4000
ing getName() {
return name;
}

public int getImageId() {
return imageId;
}
}

2.创建子布局

<?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"
/>
<!--只有其右边没有同级子控件的时候,设置layout_marginRight
* 才是相对于父控件的最右边而言的-->

<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.自定义适配器

package com.caobo.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;

public class FruitAdapter extends ArrayAdapter<Fruit> {
private int resourceId;

//重写构造函数，将上下文，子项布局Id,数据传递进来
public FruitAdapter(Context context,int textViewResourceId, List<Fruit> objects) {
super(context, textViewResourceId, objects);
resourceId=textViewResourceId;
}

//重写getview方法

@Override
public View getView(int position, View convertView, ViewGroup parent) {
//获取当前fruit实例
Fruit fruit = getItem(position);
//inflate的两个参数分别是要加载的布局文件的id，和添加一个父布局
//加一个判断，如果converView不为空，那么就直接使用，提高了运行效率，不用每一次都加载布局，convertView是缓存
View view;
ViewHolder viewHolder;

if (convertView==null) {
view = LayoutInflater.from(getContext()).inflate(resourceId,null);
viewHolder = new ViewHolder();
//将控件加载然后放到viewholder对象中
viewHolder.fruitImage = (ImageView) view.findViewById(R.id.fruit_image);
viewHolder.fruitName = (TextView) view.findViewById(R.id.fruit_name);
view.setTag(viewHolder);//将viewHolder对象存储在view中
} else {
view = convertView;
viewHolder = (ViewHolder) view.getTag();//重新获取viewholder
}
//优化
/*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());*/

viewHolder.fruitImage.setImageResource(fruit.getImageId());
viewHolder.fruitName.setText(fruit.getName());

return view;
}

//获取控件实例,自定义
class ViewHolder{
ImageView fruitImage;
TextView fruitName;
}

}

4.活动中代码怎么写

package com.caobo.listviewtest;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends Activity {
/* private String[] data = {"Apple","Banana","Orange","Watermelon","Pear",
"Grape","Pineapple","Strawberry","Cherry","Mango","caobo","mengmeng",
"caozhi","xiaohuo","zhangpeng","fahter","mother"};*/

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

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//数组中的数据是无法直接传递给ListView的，需要记住适配器来完成
//一个参数为上下文context对象,第一个参数是listview的子布局Id,这里我们使用的是内置的布局文件,
//可用于显示简单的文字,第三个参数是数据
/* ArrayAdapter<String> adapter = new ArrayAdapter<String>(MainActivity.this,
android.R.layout.simple_list_item_1, data);

ListView listView = (ListView) findViewById(R.id.list_view);
//将构建好的适配器对象传递进去,listview和数据之间的关联就建立好了
listView.setAdapter(adapter);*/

//自定义的listview
//初始化水果
initFruits();

FruitAdapter adapter = new FruitAdapter(MainActivity.this, R.layout.fruit_item, mFruitList);
ReFlashListView listView = (ReFlashListView) findViewById(R.id.list_view);
listView.setAdapter(adapter);
//创建一个监听器
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
//点击listview中的任何一个子项都会回调这个方法，同position获取到位置是哪一个子项
//我自定义的有一个Header，所以位置会错误.去掉即可
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) {
Fruit fruit = mFruitList.get(position);
Toast.makeText(MainActivity.this, fruit.getName(), Toast.LENGTH_SHORT).show();
}
});

}

private  void  initFruits(){
//Apple是显示在列表中的名字
Fruit apple = new Fruit("Apple", R.drawable.apple);
mFruitList.add(apple);
Fruit banana = new Fruit("Banana",R.drawable.banana);
mFruitList.add(banana);
Fruit orange = new Fruit("Orange",R.drawable.orange);
mFruitList.add(orange);
Fruit watermelon = new Fruit("Watermelon",R.drawable.watermelon);
mFruitList.add(watermelon);
Fruit pear = new Fruit("Pear",R.drawable.pear);
mFruitList.add(pear);
Fruit grape = new Fruit("Grape",R.drawable.grape);
mFruitList.add(grape);
Fruit pineapple = new Fruit("Pineapple",R.drawable.pine);
mFruitList.add(pineapple);
Fruit starwberry = new Fruit("Starwberry",R.drawable.star);
mFruitList.add(starwberry);
Fruit cherry = new Fruit("Cherry",R.drawable.erryy);
mFruitList.add(cherry);
/*Fruit mange = new Fruit("Mange",R.drawable.mango);
mFruitList.add(mange);*/
}
}

3.优化listView效率

重点看getView中和上面的自定义适配器的区别，数组不一样，没更改,子布局也是

public class msgAdapter extends ArrayAdapter<Msg> {

private int resourceId;

public msgAdapter(Context context,int textViewResourceId, List<Msg> objects) {
super(context, textViewResourceId, objects);
resourceId=textViewResourceId;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
//获取实例
Msg msg = getItem(position);
View view;
ViewHolder viewHolder;
if (convertView == null) {
//如果converView缓存为空则重新加载布局
view = LayoutInflater.from(getContext()).inflate(resourceId, null);
//将加载的布局全部放入viewHolder中
viewHolder = new ViewHolder();
viewHolder.leftLayout = (LinearLayout) view.findViewById(R.id.left_layout);
viewHolder.rightLayout = (LinearLayout) view.findViewById(R.id.right_layout);
viewHolder.leftMsg = (TextView) view.findViewById(R.id.left_msg);
viewHolder.rightMsg = (TextView) view.findViewById(R.id.right_msg);
//把holder对象放入view中
view.setTag(viewHolder);
} else {
//如果缓存不为空,直接使用,并去除viewholder
view=convertView;
viewHolder = (ViewHolder) view.getTag();
}
//增加对消息类型的判断
if (msg.getType()==Msg.TYPE_RECEVIED){
//如果是收到消息，则显示左边的消息布局，将右边的消息布局隐藏
viewHolder.leftLayout.setVisibility(View.VISIBLE);
viewHolder.rightLayout.setVisibility(View.GONE);
viewHolder.leftMsg.setText(msg.getContent());
}else {
viewHolder.rightLayout.setVisibility(View.VISIBLE);
viewHolder.leftLayout.setVisibility(View.GONE);
viewHolder.rightMsg.setText(msg.getContent());
}

return view;

}

class ViewHolder{
//这里是listview的子布局控件
LinearLayout leftLayout;

LinearLayout rightLayout;

TextView leftMsg;

TextView rightMsg;
}
}

运行图如下