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脚本之家。