Android 通过ViewHolder优化适配器的实现方法(必看)

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;
  }
}

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;
 }
}

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;
 }
}

<?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>

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; 
  } 
} 

  @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; 
  }