Android控件开发之四----ListView(4)
16lz
2021-01-24
下面介绍下baseAdapter这个迭代器的基类,可以任由自己发挥,实现自己的迭代器。。。。
继承图如下:
public abstract class BaseAdapter extends Object implements ListAdapter SpinnerAdapter java.lang.Object ↳android.widget.BaseAdapterKnown Direct Subclasses ArrayAdapter<T>, CursorAdapter, SimpleAdapter Known Indirect Subclasses ResourceCursorAdapter, SimpleCursorAdapter
官网上对她的解释:
Common base class of common implementation for an Adapter that can be used in both ListView (by implementing the specialized ListAdapter interface} and Spinner (by implementing the specialized SpinnerAdapter interface.(实现adapter基类被用于listview和spinner)
实现这个抽象类必须实现四个接口:
public int getCount()public View getView(int position, View convertView, ViewGroup parent) //这个最重要,显示Item中的View,只要更新了ui,这个接口一定会被调用public long getItemId(int position)public Object getItem(int position)
下面直接上代码,介绍一些BaseAdapter的技巧package com.potato;import java.util.ArrayList;import java.util.HashMap;import java.util.Map;import android.app.ListActivity;import android.os.Bundle;import android.view.View;import android.widget.ListView;import android.widget.Toast;public class ListViewBaseAdapterDemoActivity extends ListActivity {// 展示的文字private final static String[] texts = new String[] { "Aries", "Taurus","Gemini", "Cancer", "Leo", "Virgo", "Gemini Libra ", "Scorpio","Sagittarius", "Capricorn", "Aquarius", "Pisces" };private ArrayList<Map<String, Object>> mData = new ArrayList<Map<String, Object>>();/** Called when the activity is first created. */@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);for (int i = 0; i < texts.length; i++) {Map<String, Object> map = new HashMap<String, Object>();map.put("text", texts[i]);map.put("image", R.drawable.ic_launcher);mData.add(map);}// 设置一个Adapter,使用自定义的AdaptersetListAdapter(new TextImageAdapter(this, mData));}@Overrideprotected void onListItemClick(ListView l, View v, int position, long id) {Toast.makeText(this, "您单击了" + texts[position], Toast.LENGTH_SHORT).show();}}
TextImageAdapter.java
package com.potato;import java.util.ArrayList;import java.util.Map;import android.content.Context;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.ImageView;import android.widget.TextView;public class TextImageAdapter extends BaseAdapter {private ContextmContext = null;private ArrayList<Map<String, Object>> mData = null;public TextImageAdapter(Context context, ArrayList<Map<String, Object>> data){this.mContext = context;this.mData = data;}/** * 元素的个数 */public int getCount(){return mData.size();}/** * 获取对应的对象 */public Object getItem(int position){return mData.get(position);}/** * 获取id */public long getItemId(int position){return position;}// 用以生成在ListView中展示的一个个元素Viewpublic View getView(int position, View convertView, ViewGroup parent) // 注4{ItemViewCache cache = null;// 优化ListView注1if (convertView == null){convertView = LayoutInflater.from(mContext).inflate( // 注5R.layout.list_item, null);cache = new ItemViewCache();cache.mTextView = (TextView) convertView.findViewById(R.id.text);cache.mImageView = (ImageView) convertView.findViewById(R.id.image);convertView.setTag(cache); // 注6} else{cache = (ItemViewCache) convertView.getTag(); // 注6}// 设置文本和图片,然后返回这个View,用于ListView的Item的展示cache.mTextView.setText((String)mData.get(position).get("text"));cache.mImageView.setImageResource((Integer)mData.get(position).get("image"));return convertView;}// 元素的缓冲类,用于优化ListView 注2public static class ItemViewCache{public TextViewmTextView;public ImageViewmImageView;}}注1:
注2:
注4:
这里说下几个技巧,提高效率
由于listitem的UI一更新就会调用getview,而在listview中有一些数据已经有了,无需增加,只要重新利用就可以了
所以增加了判断,
if (convertView == null)这样就会过滤掉那些已经有的view;
注6:
convertView.setTag(cache);cache = (ItemViewCache) convertView.getTag();这里getTag,setTag类似于控件的Id,分辨各个view用的,这样才能实现过滤;注5:
convertView = LayoutInflater.from(mContext).inflate( R.layout.list_item, null);先生成LayoutInflater(作用:把xml的布局转换成view对象,详细的后文会叙说)的一个对象,LayoutInflater.from(mContext)接着就是布局自己的文件,生成view
list_item.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" android:background="#FFFFFF"> <TextView android:id="@+id/text" android:layout_alignParentLeft="true" android:layout_width="wrap_content" android:layout_height="wrap_content"/> <ImageView android:id="@+id/image" android:layout_alignParentRight="true" android:layout_width="wrap_content" android:layout_height="wrap_content"/></RelativeLayout>
更多相关文章
- Android(安卓)使用RecyclerView的方法
- [置顶] Android(安卓)IPC 通讯机制源码分析【下】
- Android(安卓)Wifi --自动连接指定SSID(各种加密方式均可)
- android4.4.2 bluetooth解析(二)
- 使用ViewSwitcher和ViewFlipper在不同布局中切换
- strut2服务器与android交互数据
- android 底部弹出提示框的实现方式
- Android中LayoutInflater实例
- Android中实现短信发送的一种方式