Android ListView 基礎入門 簡介以及深入優化

ListView 簡介

ListView 是安卓里常用的控件， 本文介紹一下常用用法，以及優化等方法

改寫 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>

新建一個 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 每個元素的視圖

<?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>

新建一個class IconAdapter 繼承自 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
這兒有了一個優化, convertView 將之前的布局進行緩存, 以便之后進行重用.

所以我們判斷convertView是否為空. 空的話就使用LayoutInflater去加載布局, 否則的話就直接復用convertView

關于 ArrayAdapter 可以參閱這篇博客
Android ArrayAdapter 源碼查看 深入了解

</blockquote>

測試listview

MainActivity里面加入下面代碼

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);
}



}</pre> 效果圖如下： 
 
 
   
 
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