Android中EfficientAdapte如何使用
今天就跟大家聊聊有关Android中EfficientAdapte如何使用,可能很多人都不太了解,为了让大家更加了解,小编给大家总结了以下内容,希望大家根据这篇文章可以有所收获。
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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:
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
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"}; }
看完上述内容,你们对Android中EfficientAdapte如何使用有进一步的了解吗?如果还想了解更多知识或者相关内容,请关注创新互联行业资讯频道,感谢大家的支持。
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