Adapter類的定義:
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Adapter對象是AdapterView和底層數(shù)據(jù)見的橋梁。Adapter用于訪問數(shù)據(jù)項,并且負(fù)責(zé)為數(shù)據(jù)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(diào)用Adapter的getView()方法創(chuàng)建并添加每個子條目的視圖。Adapter的getView()方法就是用來創(chuàng)建這些視圖的,Adapter并不會為每行數(shù)據(jù)都創(chuàng)建一個新視圖,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UI控件的引用,然后使用與當(dāng)前項的位置綁定的數(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時都會調(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,希望能給大家一個參考,也希望大家多多支持創(chuàng)新互聯(lián)。
網(wǎng)站標(biāo)題:Android通過ViewHolder優(yōu)化適配器的實現(xiàn)方法(必看)
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