深入浅出学习Android ListView基础

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

1、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>

2、新建一个javabean

package com.example.tomchen.testlistview;
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;
  }
}

3、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>

4、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;
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

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：

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