Android ListView 基础入门 简介以及深入优化

ListView 简介

ListView 是安卓里常用的控件， 本文介绍一下常用用法，以及优化等方法

本文地址 http://blog.csdn.net/never_cxb/article/details/48159717。转载请注明出处

改写 activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

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

</LinearLayout>

新建一个 javabean

package com.example.tomchen.testlistview;

/**
 * Created by tomchen on 9/1/15.
 */
public class Icon {
    private int imageId;
    private String name;

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

    public String getName() {
        return name;
    }

    public int getImageId() {
        return imageId;
    }
}

新建icon_item.xml 用于 listview 每个元素的视图

<?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"
    android:orientation="horizontal">

    <TextView
        android:id="@+id/text"
        android:layout_width="wrap_content"
        android:layout_height="match_parent" />

    <ImageView
        android:id="@+id/icon"
        android:layout_width="wrap_content"
        android:layout_height="match_parent" />

</LinearLayout>

新建一个class IconAdapter 继承自 ArrayAdapter

package com.example.tomchen.testlistview;

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 tomchen on 9/1/15.
 */
public class IconAdapter extends ArrayAdapter<Icon> {
    private int resourceId;


    public IconAdapter(Context context, int resource, List<Icon> icons) {
        super(context, resource, icons);
        this.resourceId = resource;
    }


    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        Icon icon = getItem(position);
        View view;
        if (convertView == null) {
            view = LayoutInflater.from(getContext()).inflate(resourceId, null);
        } else {
            view = convertView;
        }
        ImageView image = (ImageView) view.findViewById(R.id.icon);
        image.setImageResource(icon.getImageId());
        TextView text = (TextView) view.findViewById(R.id.text);
        text.setText(icon.getName());
        return view;
    }
}

Note
这儿有了一个优化, convertView 将之前的布局进行缓存, 以便之后进行重用.

所以我们判断convertView是否为空. 空的话就使用LayoutInflater去加载布局, 否则的话就直接复用convertView

关于 ArrayAdapter 可以参阅这篇博客
Android ArrayAdapter 源码查看 深入了解

测试listview

MainActivity里面加入下面代码

package com.example.tomchen.testlistview;


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

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

public class MainActivity extends AppCompatActivity {
    private ListView listView;
    private List<Icon> icons = new ArrayList<Icon>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listView = (ListView) findViewById(R.id.listview);
        icons.add(new Icon("Icon_01", R.drawable.ic_01));
        icons.add(new Icon("Icon_02", R.drawable.ic_02));
        icons.add(new Icon("Icon_03", R.drawable.ic_03));
        icons.add(new Icon("Icon_04", R.drawable.ic_04));
        icons.add(new Icon("Icon_05", R.drawable.ic_05));
        icons.add(new Icon("Icon_06", R.drawable.ic_06));
        icons.add(new Icon("Icon_07", R.drawable.ic_07));
        icons.add(new Icon("Icon_08", R.drawable.ic_08));
        icons.add(new Icon("Icon_09", R.drawable.ic_09));
        IconAdapter adapter = new IconAdapter(this, R.layout.icon_item, icons);
        listView.setAdapter(adapter);
    }


}

效果图如下：