Adapter類的定義：
Adapter對象是AdapterView和底層數據見的橋梁。Adapter用于訪問數據項，并且負責為數據項生成視圖
AdapterView是一個抽象類，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時會調用Adapter的getView()方法創建并添加每個子條目的視圖。Adapter的getView()方法就是用來創建這些視圖的，Adapter并不會為每行數據都創建一個新視圖，而是提供了回收舊視圖的方法。運行機制簡單說就是當getView()方法被調用是，如果convertView參數不為null,就使用convertView，不用新建視圖，通過convertView.findViewById()方法獲取每個UI控件的引用，然后使用與當前項的位置綁定的數據來填充視圖
為了優化，使用ViewHolder模式，ViewHolder是一個靜態類，可以用于保存每行的視圖以避免每次調用getView時都會調用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>
以上代碼就基本實現了功能
不過每次都自定義ViewHolder比較繁瑣，在網上找了一個工具類，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優化適配器的實現方法(必看)就是小編分享給大家的全部內容了，希望能給大家一個參考，也希望大家多多支持億速云。
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