十、高级控件之ListView

上课视频：
链接:https://pan.baidu.com/s/1xR5jJBiU2vwiW2pE6AD5nA 密码:eg01

一、ListView 的使用场景

展示一些重复格式数据的列表，如消息列表，音乐列表。

二、ListView所用的设计模式介绍

ListView所用的设计模式是适配器模式，更多适配器想关设计模式介绍看下面地址：
http://www.runoob.com/design-pattern/adapter-pattern.html

三、ListView的使用。

使用ListView控件需要三个类
1.ListView本身控件
2.ListView的适配器，适配器要依赖数据集和Activity本身
3.数据集。

上课代码：
Activity中的代码

package com.joychen.www.a11listviewdemo;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ListView;

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

public class MainActivity extends AppCompatActivity {

    private ListView listView;
    private MessageAdapter myadapter;

    private List<MessageBean> msgList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listView = findViewById(R.id.mylistv);
        msgList = getMessageList();
        myadapter = new MessageAdapter(msgList,this);
        listView.setAdapter(myadapter);

    }


    private List<MessageBean> getMessageList(){
        List<MessageBean> list = new ArrayList<>();
        for (int i=0;i<30;i++){
            MessageBean mb = new MessageBean(i+"","","小明"+i,"最后一条消息"+i);
            list.add(mb);
        }

        return list;
    }

}

Activity中依赖的布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:orientation="vertical"
    android:layout_height="match_parent">
    <TextView
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:gravity="center"
        android:textColor="#fff"
        android:background="@color/colorPrimary"
        android:text="ListView控件使用"
        />

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

</LinearLayout>

适配器MessageAdapter代码

package com.joychen.www.a11listviewdemo;

import android.app.Activity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.List;

/**
 * Created by joychen on 2018/5/2.
 */

public class MessageAdapter extends BaseAdapter {

    private List<MessageBean> data;
    private Activity activity;

    public MessageAdapter(List<MessageBean> data,Activity activity){
        this.data = data;
        this.activity = activity;
    }


    @Override
    public int getCount() {
        return data.size();
    }

    @Override
    public Object getItem(int position) {
        return data.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View view =  LayoutInflater.from(activity).inflate(R.layout.item_message_lv,null);
        TextView name = view.findViewById(R.id.firend_name_txt);
        TextView message = view.findViewById(R.id.last_message_txt);
        TextView time = view.findViewById(R.id.time_txt);

        MessageBean mb = data.get(position);
        name.setText(mb.getName());
        message.setText(mb.getLastMessage());
        time.setText(getTime(mb.getTime()));
        return view;
    }

    private String getTime(long t){
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
        return format.format(new Date(t));
    }
}

实体MessageBean

package com.joychen.www.a11listviewdemo;

import java.util.Date;

/**
 * Created by joychen on 2018/5/2.
 */

public class MessageBean {
    private String id;
    private String head;
    private String name;
    private String lastMessage;
    private long time = new Date().getTime();

    public MessageBean() {

    }

    /**
     *
     * @param id
     * @param head
     * @param name
     * @param lastMessage
     */
    public MessageBean(String id, String head, String name, String lastMessage) {
        this.id = id;
        this.head = head;
        this.name = name;
        this.lastMessage = lastMessage;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getHead() {
        return head;
    }

    public void setHead(String head) {
        this.head = head;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getLastMessage() {
        return lastMessage;
    }

    public void setLastMessage(String lastMessage) {
        this.lastMessage = lastMessage;
    }

    public long getTime() {
        return time;
    }

    public void setTime(long time) {
        this.time = time;
    }
}

四、ListView的内存优化