Android ListView之EfficientAdapte的使用详解

概述AndroidListView之EfficientAdapte的使用详解在做Android手机应用开发时，ListView是一个非常常用的控件。如何更新的使用它呢？其实SDK中的例子已经非常的完整了，并且能满足大多数的需要。

AndroID ListVIEw之EfficIEntAdapte的使用详解

在做AndroID手机应用开发时， ListVIEw是一个非常常用的控件。如何更新的使用它呢？其实SDK中的例子已经非常的完整了，并且能满足大多数的需要。

    如果大家刚开始学习ListVIEw，我建议大家还是直接先看官方的例子好了，这样大家会学到更好的写法以及养成更好的习惯。

    下面就以EfficIEntAdapter为例，看看官网例子是如何使用ListVIEw的：

    请大家格外注意getVIEw的书写方法，大家可能从网上也能找到过一些其它的例子，但是网上的写法和官网不同，建议大家采用官网例子的写法。

    简要说明：要实现高效的Adapter，需要做两件事： 

    1. 重用getVIEw()中的convertVIEw，避免在不必要的时候inflating VIEw。 

    2. 使用VIEwHolder模式，避免在不必要的时候调用findVIEwByID()。

    顺便再提一句：若继承的是ListActivity，如果在layout xml里定义了ListVIEw，那么该ListVIEw的ID必须是"@ID/androID:List"，最好再包含一个ID是"@ID/androID:empty"的TextVIEw，供ListVIEw中没有数据时，显示提示文字用。如下所示：

Xml代码 

<?xml version="1.0" enCoding="utf-8"?>  <linearLayout xmlns:androID="http://schemas.androID.com/apk/res/androID"      androID:orIEntation="vertical"      androID:layout_wIDth="match_parent"      androID:layout_height="match_parent"      androID:paddingleft="8dp"      androID:paddingRight="8dp">     <ListVIEw androID:ID="@ID/androID:List"         androID:layout_wIDth="match_parent"         androID:layout_height="match_parent"         androID:background="#00FF00"         androID:layout_weight="1"         androID:drawSelectorOntop="false"/>     <TextVIEw androID:ID="@ID/androID:empty"         androID:layout_wIDth="match_parent"         androID:layout_height="match_parent"         androID:background="#FF0000"         androID:text="No data"/>  </linearLayout> 

    官网EfficIEntAdapter例子如下：

Java代码 

/**  * Demonstrates how to write an efficIEnt List adapter. The adapter used in this example binds  * to an ImageVIEw and to a TextVIEw for each row in the List.  *  * To work efficIEntly the adapter implemented here uses two techniques:  * - It reuses the convertVIEw passed to getVIEw() to avoID inflating VIEw when it is not necessary  * - It uses the VIEwHolder pattern to avoID calling findVIEwByID() when it is not necessary  *  * The VIEwHolder pattern consists in storing a data structure in the tag of the vIEw returned by  * getVIEw(). This data structures contains references to the vIEws we want to bind data to,thus  * avoIDing calls to findVIEwByID() every time getVIEw() is invoked.  */ public class List14 extends ListActivity {    private static class EfficIEntAdapter extends BaseAdapter {     private LayoutInflater mInflater;     private Bitmap mIcon1;     private Bitmap mIcon2;      public EfficIEntAdapter(Context context) {       // Cache the LayoutInflate to avoID asking for a new one each time.       mInflater = LayoutInflater.from(context);        // Icons bound to the rows.       mIcon1 = BitmapFactory.decodeResource(context.getResources(),R.drawable.icon48x48_1);       mIcon2 = BitmapFactory.decodeResource(context.getResources(),R.drawable.icon48x48_2);     }      /**      * The number of items in the List is determined by the number of speeches      * in our array.      *      * @see androID.Widget.listadapter#getCount()      */     public int getCount() {       return DATA.length;     }      /**      * Since the data comes from an array,just returning the index is      * sufficent to get at the data. If we were using a more complex data      * structure,we would return whatever object represents one row in the      * List.      *      * @see androID.Widget.listadapter#getItem(int)      */     public Object getItem(int position) {       return position;     }      /**      * Use the array index as a unique ID.      *      * @see androID.Widget.listadapter#getItemID(int)      */     public long getItemID(int position) {       return position;     }      /**      * Make a vIEw to hold each row.      *      * @see androID.Widget.listadapter#getVIEw(int,androID.vIEw.VIEw,*   androID.vIEw.VIEwGroup)      */     public VIEw getVIEw(int position,VIEw convertVIEw,VIEwGroup parent) {       // A VIEwHolder keeps references to children vIEws to avoID unneccessary calls       // to findVIEwByID() on each row.       VIEwHolder holder;        // When convertVIEw is not null,we can reuse it directly,there is no need       // to reinflate it. We only inflate a new VIEw when the convertVIEw supplIEd       // by ListVIEw is null.       if (convertVIEw == null) {         convertVIEw = mInflater.inflate(R.layout.List_item_icon_text,null);          // Creates a VIEwHolder and store references to the two children vIEws         // we want to bind data to.         holder = new VIEwHolder();         holder.text = (TextVIEw) convertVIEw.findVIEwByID(R.ID.text);         holder.icon = (ImageVIEw) convertVIEw.findVIEwByID(R.ID.icon);          convertVIEw.setTag(holder);       } else {         // Get the VIEwHolder back to get fast access to the TextVIEw         // and the ImageVIEw.         holder = (VIEwHolder) convertVIEw.getTag();       }        // Bind the data efficIEntly with the holder.       holder.text.setText(DATA[position]);       holder.icon.setimageBitmap((position & 1) == 1 ? mIcon1 : mIcon2);        return convertVIEw;     }      static class VIEwHolder {       TextVIEw text;       ImageVIEw icon;     }   }    @OverrIDe   public voID onCreate(Bundle savedInstanceState) {     super.onCreate(savedInstanceState);     setlistadapter(new EfficIEntAdapter(this));   }    private static final String[] DATA = {       "Abbaye de Belloc","Abbaye du Mont des Cats","Abertam"}; } 

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