这里有新鲜出炉的精品教程,程序狗速度看过来!
Android是一种基于Linux的自由及开放源代码的操作系统,主要使用于移动设备,如智能手机和平板电脑,由Google公司和开放手机联盟领导及开发。尚未有统一中文名称,中国大陆地区较多人使用“安卓”或“安致”。
这篇文章主要介绍了Android ListView之EfficientAdapte的使用详解的相关资料,这里介绍EfficientAdapter 的使用方法,需要的朋友可以参考下
Android ListView之EfficientAdapte的使用详解
在做Android手机应用开发时, ListView是一个非常常用的控件。如何更新的使用它呢?其实SDK中的例子已经非常的完整了,并且能满足大多数的需要。
如果大家刚开始学习ListView,我建议大家还是直接先看官方的例子好了,这样大家会学到更好的写法以及养成更好的习惯。
下面就以EfficientAdapter为例,看看官网例子是如何使用ListView的:
请大家格外注意getView的书写方法,大家可能从网上也能找到过一些其它的例子,但是网上的写法和官网不同,建议大家采用官网例子的写法。
简要说明:要实现高效的Adapter,需要做两件事:
1. 重用getView()中的convertView,避免在不必要的时候inflating View。
2. 使用ViewHolder模式,避免在不必要的时候调用findViewById()。
顺便再提一句:若继承的是ListActivity,如果在layout xml里定义了ListView,那么该ListView的ID必须是"@id/android:list",最好再包含一个ID是"@id/android:empty"的TextView,供ListView中没有数据时,显示提示文字用。如下所示:
Xml代码
- <?xml version="1.0" encoding="utf-8"?>
- <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
- android:orientation="vertical"
- android:layout_width="match_parent"
- android:layout_height="match_parent"
- android:paddingLeft="8dp"
- android:paddingRight="8dp">
- <ListView android:id="@id/android:list"
- android:layout_width="match_parent"
- android:layout_height="match_parent"
- android:background="#00FF00"
- android:layout_weight="1"
- android:drawSelectorOnTop="false"/>
- <TextView android:id="@id/android:empty"
- android:layout_width="match_parent"
- android:layout_height="match_parent"
- android:background="#FF0000"
- android:text="No data"/>
- </LinearLayout>
官网EfficientAdapter例子如下:
Java代码
- /**
- * Demonstrates how to write an efficient list adapter. The adapter used in this example binds
- * to an ImageView and to a TextView for each row in the list.
- *
- * To work efficiently the adapter implemented here uses two techniques:
- * - It reuses the convertView passed to getView() to avoid inflating View when it is not necessary
- * - It uses the ViewHolder pattern to avoid calling findViewById() when it is not necessary
- *
- * The ViewHolder pattern consists in storing a data structure in the tag of the view returned by
- * getView(). This data structures contains references to the views we want to bind data to, thus
- * avoiding calls to findViewById() every time getView() is invoked.
- */
- public class List14 extends ListActivity {
- private static class EfficientAdapter extends BaseAdapter {
- private LayoutInflater mInflater;
- private Bitmap mIcon1;
- private Bitmap mIcon2;
- public EfficientAdapter(Context context) {
- // Cache the LayoutInflate to avoid asking for a new one each time.
- mInflater = LayoutInflater.from(context);
- // Icons bound to the rows.
- mIcon1 = BitmapFactory.decodeResource(context.getResources(), R.drawable.icon48x48_1);
- mIcon2 = BitmapFactory.decodeResource(context.getResources(), R.drawable.icon48x48_2);
- }
- /**
- * The number of items in the list is determined by the number of speeches
- * in our array.
- *
- * @see android.widget.ListAdapter#getCount()
- */
- public int getCount() {
- return DATA.length;
- }
- /**
- * Since the data comes from an array, just returning the index is
- * sufficent to get at the data. If we were using a more complex data
- * structure, we would return whatever object represents one row in the
- * list.
- *
- * @see android.widget.ListAdapter#getItem(int)
- */
- public Object getItem(int position) {
- return position;
- }
- /**
- * Use the array index as a unique id.
- *
- * @see android.widget.ListAdapter#getItemId(int)
- */
- public long getItemId(int position) {
- return position;
- }
- /**
- * Make a view to hold each row.
- *
- * @see android.widget.ListAdapter#getView(int, android.view.View,
- * android.view.ViewGroup)
- */
- public View getView(int position, View convertView, ViewGroup parent) {
- // A ViewHolder keeps references to children views to avoid unneccessary calls
- // to findViewById() on each row.
- ViewHolder holder;
- // When convertView is not null, we can reuse it directly, there is no need
- // to reinflate it. We only inflate a new View when the convertView supplied
- // by ListView is null.
- if (convertView == null) {
- convertView = mInflater.inflate(R.layout.list_item_icon_text, null);
- // Creates a ViewHolder and store references to the two children views
- // we want to bind data to.
- holder = new ViewHolder();
- holder.text = (TextView) convertView.findViewById(R.id.text);
- holder.icon = (ImageView) convertView.findViewById(R.id.icon);
- convertView.setTag(holder);
- } else {
- // Get the ViewHolder back to get fast access to the TextView
- // and the ImageView.
- holder = (ViewHolder) convertView.getTag();
- }
- // Bind the data efficiently with the holder.
- holder.text.setText(DATA[position]);
- holder.icon.setImageBitmap((position & 1) == 1 ? mIcon1: mIcon2);
- return convertView;
- }
- static class ViewHolder {
- TextView text;
- ImageView icon;
- }
- }
- @Override public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setListAdapter(new EfficientAdapter(this));
- }
- private static final String[] DATA = {
- "Abbaye de Belloc",
- "Abbaye du Mont des Cats",
- "Abertam"
- };
- }
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来源: http://www.phperz.com/article/17/0912/345908.html