Android 通過ViewHolder優(yōu)化適配器的實(shí)現(xiàn)方法(必看)

更新時(shí)間：2017年04月18日 09:52:00 投稿：jingxian

下面小編就為大家?guī)硪黄狝ndroid 通過ViewHolder優(yōu)化適配器的實(shí)現(xiàn)方法(必看)。小編覺得挺不錯(cuò)的，現(xiàn)在就分享給大家，也給大家做個(gè)參考。一起跟隨小編過來看看吧

Adapter類的定義：

Adapter對(duì)象是AdapterView和底層數(shù)據(jù)見的橋梁。Adapter用于訪問數(shù)據(jù)項(xiàng)，并且負(fù)責(zé)為數(shù)據(jù)項(xiàng)生成視圖

AdapterView是一個(gè)抽象類，用于那些需要通過Adapter填充自身的視圖，其常見子類是ListView。顯示AdapterView時(shí)會(huì)調(diào)用Adapter的getView()方法創(chuàng)建并添加每個(gè)子條目的視圖。Adapter的getView()方法就是用來創(chuàng)建這些視圖的，Adapter并不會(huì)為每行數(shù)據(jù)都創(chuàng)建一個(gè)新視圖，而是提供了回收舊視圖的方法。運(yùn)行機(jī)制簡單說就是當(dāng)getView()方法被調(diào)用是，如果convertView參數(shù)不為null,就使用convertView，不用新建視圖，通過convertView.findViewById()方法獲取每個(gè)UI控件的引用，然后使用與當(dāng)前項(xiàng)的位置綁定的數(shù)據(jù)來填充視圖

為了優(yōu)化，使用ViewHolder模式，ViewHolder是一個(gè)靜態(tài)類，可以用于保存每行的視圖以避免每次調(diào)用getView時(shí)都會(huì)調(diào)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>

以上代碼就基本實(shí)現(xiàn)了功能

不過每次都自定義ViewHolder比較繁瑣，在網(wǎng)上找了一個(gè)工具類，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; 
  }

以上這篇Android 通過ViewHolder優(yōu)化適配器的實(shí)現(xiàn)方法(必看)就是小編分享給大家的全部內(nèi)容了，希望能給大家一個(gè)參考，也希望大家多多支持腳本之家。

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