ArrayAdapter详解：ArrayAdapter(Context context, int textViewResourceId, T[] objects)

ArrayAdapter详解

ArrayAdapter(Context context, int textViewResourceId, T[] objects)

1、定义：android.widget.ArrayAdapter<T>

ArrayAdapter常用6个构造方法：

ArrayAdapter(Context context, int textViewResourceId)

ArrayAdapter(Context context, int resource, inttextViewResourceId)

ArrayAdapter(Context context, inttextViewResourceId, T[] objects)

ArrayAdapter(Context context, int resource, inttextViewResourceId, T[] objects)

ArrayAdapter(Context context, inttextViewResourceId, List<T> objects)

ArrayAdapter(Contextcontext, intresource, inttextViewResourceId, List<T>objects)

2、参数说明：

（1）context ： The current context.（传递Context对象，一般为this）

（2）resource ： The id of the TextView within the layout resource to be populated：该布局资源在res/layout/Xxx.xml中定义后会自动在R.java文件中生成对应的ID，然后利用R.layout.Xxx调用即可，也可以使用系统已定义好的布局文件，比如：

android.R.layout.simple_list_item_1（前面必须加上android否则出错）

android.R.layout.simple_expandable_list_item_1等等。

注意：布局文件必须是关于TextView组件的XML文件（也可以TextView类的子类组件，如Button, CheckedTextView, Chronometer, DigitalClock, EditText, TextClock都是TextView的子类），列表项的每个条项都是按照这个TextView组件进行显示。

（3）textViewResourceId：对应的是resource布局文件中TextView组件的ID；

（4

）objects ：

The objects to represent in the ListView.数组或者List集合，用于为多个列表项提供数据

从中可知：textViewResourceId用于控制每个列表项的TextView组件（控制布局形式显示风格），而objects（数组或者List集合）为每个列表项的TextView组件提供显示数据。数组或者List集合有多少个元素，将会生成多少个列表项。

3、 resource和textViewResourceId参数区别：

resource对应的是布局XML资源文件，而textViewResourceId指的是XML资源文件中textView组件的ID。问题来了，为什么ArrayAdapter构造方法都需要传入TextViewResourceId，有时不需要传入resource参数。例如给构造方法ArrayAdapter<String>(Context context, int textViewResourceId, String[] objects)传入参数是这样的new ArrayAdapter<String>(this, R.layout.array_item, arr1);你会发现此时textViewResourceId传入的参数是R.layout.array_item不是组件textView的ID，而是布局文件的ID，Why？？？？？？？

先来看看ArrayAdapter源码先！！！！！！！！你回惊奇的发现，ArrayAdapter的6个构造方法都调用了一个init()方法：

/**
     * Constructor
     *
     * @param context The current context.
     * @param textViewResourceId The resource ID for a layout file containing a TextView to use when
     *                 instantiating views.
     */
    public ArrayAdapter(Context context, int textViewResourceId) {
        init(context, textViewResourceId, 0, new ArrayList<T>());
    }

    /**
     * Constructor
     *
     * @param context The current context.
     * @param resource The resource ID for a layout file containing a layout to use when
     *                 instantiating views.
     * @param textViewResourceId The id of the TextView within the layout resource to be populated
     */
    public ArrayAdapter(Context context, int resource, int textViewResourceId) {
        init(context, resource, textViewResourceId, new ArrayList<T>());
    }

    /**
     * Constructor
     *
     * @param context The current context.
     * @param textViewResourceId The resource ID for a layout file containing a TextView to use when
     *                 instantiating views.
     * @param objects The objects to represent in the ListView.
     */
    public ArrayAdapter(Context context, int textViewResourceId, T[] objects) {
        init(context, textViewResourceId, 0, Arrays.asList(objects));
    }

    /**
     * Constructor
     *
     * @param context The current context.
     * @param resource The resource ID for a layout file containing a layout to use when
     *                 instantiating views.
     * @param textViewResourceId The id of the TextView within the layout resource to be populated
     * @param objects The objects to represent in the ListView.
     */
    public ArrayAdapter(Context context, int resource, int textViewResourceId, T[] objects) {
        init(context, resource, textViewResourceId, Arrays.asList(objects));
    }

    /**
     * Constructor
     *
     * @param context The current context.
     * @param textViewResourceId The resource ID for a layout file containing a TextView to use when
     *                 instantiating views.
     * @param objects The objects to represent in the ListView.
     */
    public ArrayAdapter(Context context, int textViewResourceId, List<T> objects) {
        init(context, textViewResourceId, 0, objects);
    }

    /**
     * Constructor
     *
     * @param context The current context.
     * @param resource The resource ID for a layout file containing a layout to use when
     *                 instantiating views.
     * @param textViewResourceId The id of the TextView within the layout resource to be populated
     * @param objects The objects to represent in the ListView.
     */
    public ArrayAdapter(Context context, int resource, int textViewResourceId, List<T> objects) {
        init(context, resource, textViewResourceId, objects);
    }

init()方法源码：

private void init(Context context, int resource, int textViewResourceId, List<T> objects) {
        mContext = context;
        mInflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        mResource = mDropDownResource = resource;
        mObjects = objects;
        mFieldId = textViewResourceId;
    }

init()的参数，你会发现init()第二个参数是resource是必须要传入的，也就是布局资源文件不可省略，而textViewResourceId默认是0。当构造方法含有resource参数时，是布局资源文件的ID，且在实例化View时，该布局资源文件包含一个TextView 组件（The resource ID for a layout file containing a TextView to use when instantiating views.）；若省略resource参数时，此时构造方法调用init()传入的第三个参数默认设置为0。

ew ArrayAdapter<String>(this, R.layout.array_item, arr1);等于new ArrayAdapter<String>(this, R.layout.array_item,R.id.TextView ,arr1);，其中R.id.TextView是布局文件array_item中的组件TextView的ID

例子1：new ArrayAdapter<BookContent.Book>(getActivity(),android.R.layout.simple_list_item_activated_1,android.R.id.text1, arr))

这里第二个参数resource：android.R.layout.simple_list_item_activated_1，该布局文件是系统自定义好的TextView组件，其ID为@android:id/text1

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@android:id/text1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceListItemSmall"
    android:gravity="center_vertical"
    android:paddingStart="?android:attr/listPreferredItemPaddingStart"
    android:paddingEnd="?android:attr/listPreferredItemPaddingEnd"
    android:background="?android:attr/activatedBackgroundIndicator"
    android:minHeight="?android:attr/listPreferredItemHeightSmall"
/>

第三个参数

textViewResourceId：

android.R.id.text1，对应的是resource布局文件中TextView组件的ID，即text1

package org.crazyit.ui;

import android.app.ListActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;

/**
 * Description:
 * <br/>site: <a href="http://www.crazyit.org">crazyit.org</a>
 * <br/>Copyright (C), 2001-2014, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee [email protected]
 * @version  1.0
 */
public class ListActivityTest extends ListActivity
{
  @Override
  public void onCreate(Bundle savedInstanceState)
  {
    super.onCreate(savedInstanceState);
    // 无需使用布局文件
    String[] arr = { "孙悟空", "猪八戒", "唐僧" };
    // 创建ArrayAdapter对象
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
      android.R.layout.simple_list_item_multiple_choice, arr);
    // 设置该窗口显示列表
    setListAdapter(adapter);
  }
}

ArrayAdapter详解：ArrayAdapter(Context context, int textViewResourceId, T[] objects)