Android 通过ViewHolder优化适配器的实现方法(必看)

adapter类的定义：

adapter对象是adapterview和底层数据见的桥梁。adapter用于访问数据项，并且负责为数据项生成视图

adapterview是一个抽象类，用于那些需要通过adapter填充自身的视图，其常见子类是listview。显示adapterview时会调用adapter的getview()方法创建并添加每个子条目的视图。adapter的getview()方法就是用来创建这些视图的，adapter并不会为每行数据都创建一个新视图，而是提供了回收旧视图的方法。运行机制简单说就是当getview()方法被调用是，如果convertview参数不为null,就使用convertview，不用新建视图，通过convertview.findviewbyid()方法获取每个ui控件的引用，然后使用与当前项的位置绑定的数据来填充视图

为了优化，使用viewholder模式，viewholder是一个静态类，可以用于保存每行的视图以避免每次调用getview时都会调用findviewbyid()

public class hack25activity extends listactivity {
  private static final int model_count = 30;
  @override
  protected void oncreate(bundle savedinstancestate) {
    super.oncreate(savedinstancestate);
    setlistadapter(new modeladapter(this, 0, buildmodels()));
  }

  private list<model> buildmodels() {
    final arraylist<model> ret = new arraylist<model>(model_count);
    for (int i = 0; i < model_count; i++) {
      final model model = new model();
      model.setimage(r.mipmap.ic_launcher);
      model.settext1("name " + i);
      model.settext2("description " + i);
      ret.add(model);
    }
    return ret;
  }
}

model.java

public class model {

 private string mtext1;
 private string mtext2;
 private int mimageresid;

 public string gettext1() {
  return mtext1;
 }

 public void settext1(string text1) {
  mtext1 = text1;
 }

 public string gettext2() {
  return mtext2;
 }

 public void settext2(string text2) {
  mtext2 = text2;
 }

 public int getimage() {
  return mimageresid;
 }

 public void setimage(int imageresid) {
  mimageresid = imageresid;
 }
}

modeladapter.java

public class modeladapter extends arrayadapter<model> {

 private layoutinflater minflater;

 public modeladapter(context context, int textviewresourceid,
   list<model> objects) {
  super(context, textviewresourceid, objects);
  minflater = layoutinflater.from(context);
 }

 @override
 public view getview(int position, view convertview, viewgroup parent) {
  final viewholder viewholder;

  if (convertview == null) {
   convertview = minflater.inflate(r.layout.row_layout, parent,
     false);

   viewholder = new viewholder();
   viewholder.imageview = (imageview) convertview
     .findviewbyid(r.id.image);
   viewholder.text1 = (textview) convertview
     .findviewbyid(r.id.text1);
   viewholder.text2 = (textview) convertview
     .findviewbyid(r.id.text2);

   convertview.settag(viewholder);

  } else {
   viewholder = (viewholder) convertview.gettag();
  }

  model model = getitem(position);
  viewholder.imageview.setimageresource(model.getimage());
  viewholder.text1.settext(model.gettext1());
  viewholder.text2.settext(model.gettext2());

  return convertview;
 }

 private static class viewholder {
  public imageview imageview;
  public textview text1;
  public textview text2;
 }
}

row_layout.xml

<?xml version="1.0" encoding="utf-8"?>

<relativelayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent"
  android:layout_height="wrap_content" >

  <imageview
    android:id="@+id/image"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignparentleft="true"
    android:layout_centervertical="true" />

  <linearlayout
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_centervertical="true"
    android:layout_torightof="@id/image"
    android:orientation="vertical" >

    <textview
      android:id="@+id/text1"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content" />

    <textview
      android:id="@+id/text2"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content" />
  </linearlayout>

</relativelayout>

以上代码就基本实现了功能

不过每次都自定义viewholder比较繁琐，在网上找了一个工具类，共享一下

viewholder.java

public class viewholder {
  public static <t extends view> t get(view view, int id) {
    sparsearray<view> viewholder = (sparsearray<view>) view.gettag();
    if (viewholder == null) { 
      viewholder = new sparsearray<view>(); 
      view.settag(viewholder); 
    } 
    view childview = viewholder.get(id); 
    if (childview == null) { 
      childview = view.findviewbyid(id); 
      viewholder.put(id, childview); 
    } 
    return (t) childview; 
  } 
} 

使用方法：

  @override 
  public view getview(int position, view convertview, viewgroup parent) { 

    if (convertview == null) { 
      convertview = layoutinflater.from(context) 
       .inflate(r.layout.banana_phone, parent, false); 
    } 

    imageview bananaview = viewholder.get(convertview, r.id.banana); 
    textview phoneview = viewholder.get(convertview, r.id.phone); 

    bananaphone bananaphone = getitem(position); 
    phoneview.settext(bananaphone.getphone()); 
    bananaview.setimageresource(bananaphone.getbanana()); 

    return convertview; 
  } 

以上这篇android 通过viewholder优化适配器的实现方法(必看)就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持。