Android 使用Listview的优化

Listview是Android中很重要的一个组件，在开发过程中使用到的Listview能站到30%，在新手开发过程中，往往会忽略对Listview的优化，在上一个项目的开发中，确实用到了很多Listview，但是没有这些Listview做过优化，软件在运行过程中会很占内存，肯定也包括这部分的原因了。所以在开发过程中要注重对Listview的优化。

现在测试一个BaseAdapter这个适配器下的优化。在主布局里面放置一个Listview。每一个item的布局文件如下

<?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:padding="10dp"
    android:orientation="horizontal" >
    <ImageView 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/ic_launcher"/>
    <LinearLayout 
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginLeft="5dp"
        android:orientation="vertical">
        <TextView 
            android:id="@+id/tv_name"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="张三"/>
        <TextView 
            android:id="@+id/tv_age"
            android:layout_marginTop="5dp"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textColor="#ff0000"
            android:text="28"/>
    </LinearLayout>

</LinearLayout>

<pre name="code" class="java">package com.example.baseadaptertest;

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

public class MainActivity extends Activity {
    private ListView listview;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        listview = (ListView) findViewById(R.id.listview);
        listview.setAdapter(new MyBaseAdapter());
    }

    class MyBaseAdapter extends BaseAdapter{

        /**
         * 返回有多少列表项
         * */
        @Override
        public int getCount() {
            // TODO Auto-generated method stub
            return 20;
        }

        @Override
        public Object getItem(int pasition) {
            // TODO Auto-generated method stub
            return null;
        }

        @Override
        public long getItemId(int position) {
            // TODO Auto-generated method stub
            return 0;
        }

        @Override
        public View getView(int position, View view, ViewGroup parent){
            LayoutInflater inflater = MainActivity.this.getLayoutInflater();
            view = inflater.inflate(R.layout.listview_item, null);
            tvName = (TextView) view.findViewById(R.id.tv_name);
            tvAge = (TextView) view.findViewById(R.id.tv_age);
            tvName.setText("zhangsan" + position);
            tvAge.setText(String.valueOf(position + 28));
            return view;
        }

    }
}

<pre name="code" class="java">if(view == null) {
    // 布局填充器对象, 用于把xml布局转换成view对象
    LayoutInflater inflater = MainActivity2.this.getLayoutInflater();
    view = inflater.inflate(R.layout.listview_item, null);
    tvName= (TextView) view.findViewById(R.id.tv_name);
    tvAge = (TextView) view.findViewById(R.id.tv_age);
    } else {
        view = view;
    }
        tvName.setText("zhangsan" + position);
        tvAge.setText(String.valueOf(position + 28));
        return view;

@Override
        public View getView(int position, View view, ViewGroup parent) {

            ViewHolder holder = null;
            //复用，可以提升效率
            if (view == null) {
                LayoutInflater inflater = MainActivity.this.getLayoutInflater();
                view = inflater.inflate(R.layout.listview_item, null);
                holder = new ViewHolder();
                holder.tvName = (TextView) view.findViewById(R.id.tv_name);
                holder.tvAge = (TextView) view.findViewById(R.id.tv_age);
                view.setTag(holder);
            }else {
                holder = (ViewHolder)view.getTag();
            }
            holder.tvName.setText("zhangsan" + position);
            holder.tvAge.setText(String.valueOf(position + 28));
            return view;
        }

    }

    static class ViewHolder {
        TextView tvName;
        TextView tvAge;
    }