【正文】
【引入】
我们一般编写listView的时候顺序是这样的：
- 需要展示的数据集List<T>
- 为这个数据集编写一个ListView
- 为这个ListView编写一个Adapter，一般继承自BaseAdapter
- 在BaseAdapter内部编写一个ViewHolder类，对应ListView里面的item控件，提高控件的查询效率
分析：
List<T>:ListView --> Adapter extends BaseAdapter --> ViewHolder
一般情况下，一个ListView对应一个Adapter类，对应一个ViewHolder类，那如果一个app中有20个ListView，我们岂不是要写20遍？所以的做法是：
- 抽取ViewHolder，作为公共的类。
- 将Adapter封装成CommonAdapter，作为公共的类。
一、传统方式编写适配器：
（1）activity_main.xml:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent"> <ListView android:id="@+id/listView" android:layout_width="match_parent" android:layout_height="match_parent"></ListView> </RelativeLayout>
(2)item_listview.xml:单个item的布局文件
1 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 2 xmlns:tools="http://schemas.android.com/tools" 3 android:layout_width="match_parent" 4 android:layout_height="match_parent" 5 android:padding="10dp"> 6 7 <TextView 8 android:id="@+id/titleTv" 9 android:layout_width="wrap_content" 10 android:layout_height="wrap_content" 11 android:singleLine="true" 12 android:text="Android新技能" 13 android:textColor="#444" 14 android:textSize="16sp" /> 15 16 <TextView 17 android:id="@+id/descTv" 18 android:layout_width="match_parent" 19 android:layout_height="wrap_content" 20 android:layout_below="@+id/titleTv" 21 android:layout_marginTop="10dp" 22 android:maxLines="2" 23 android:minLines="1" 24 android:text="Android为ListView和GridView打造万能适配器" 25 android:textColor="#898989" 26 android:textSize="16sp" /> 27 28 <TextView 29 android:id="@+id/timeTv" 30 android:paddingTop="3dp" 31 android:layout_width="wrap_content" 32 android:layout_height="wrap_content" 33 android:layout_below="@+id/descTv" 34 android:layout_marginTop="10dp" 35 android:text="2015-05-04" 36 android:textColor="#898989" 37 android:textSize="12sp" /> 38 39 <TextView 40 android:padding="2dp" 41 android:id="@+id/phoneTv" 42 android:gravity="center" 43 android:layout_width="wrap_content" 44 android:layout_height="wrap_content" 45 android:layout_below="@+id/descTv" 46 android:layout_marginTop="10dp" 47 android:background="#2ED667" 48 android:drawableLeft="@mipmap/phone" 49 android:drawablePadding="5dp" 50 android:text="10086" 51 android:textColor="#ffffff" 52 android:textSize="12sp" 53 android:layout_alignParentRight="true" /> 54 55 56 </RelativeLayout>
其对应的布局效果如下：
（3）Bean.java:ListView的数据集
1 package com.smyhvae.baseadapter.entities; 2 3 /** 4 * Created by smyhvae on 2015/5/4. 5 */ 6 public class Bean { 7 private String title; 8 private String desc; 9 private String time; 10 private String phone; 11 12 public Bean() { 13 } 14 15 public Bean(String title, String desc, String time, String phone) { 16 this.title = title; 17 18 this.desc = desc; 19 this.time = time; 20 this.phone = phone; 21 } 22 23 public String getTitle() { 24 return title; 25 } 26 27 public void setTitle(String title) { 28 this.title = title; 29 } 30 31 public String getDesc() { 32 return desc; 33 } 34 35 public void setDesc(String desc) { 36 this.desc = desc; 37 } 38 39 public String getTime() { 40 return time; 41 } 42 43 public void setTime(String time) { 44 this.time = time; 45 } 46 47 public String getPhone() { 48 return phone; 49 } 50 51 public void setPhone(String phone) { 52 this.phone = phone; 53 } 54 }
（4）MyAdapter.java:自定义适配器，继承自BaseAdapter
1 package com.smyhvae.baseadapter; 2 3 import android.content.Context; 4 import android.view.LayoutInflater; 5 import android.view.View; 6 import android.view.ViewGroup; 7 import android.widget.BaseAdapter; 8 import android.widget.TextView; 9 10 import com.smyhvae.baseadapter.entities.Bean; 11 12 import java.util.List; 13 14 /** 15 * Created by smyhvae on 2015/5/4. 16 */ 17 public class MyAdapter extends BaseAdapter { 18 private LayoutInflater mInflater; 19 private List<Bean> mDatas; 20 21 //MyAdapter需要一个Context，通过Context获得Layout.inflater，然后通过inflater加载item的布局 22 public MyAdapter(Context context, List<Bean> datas) { 23 24 mInflater = LayoutInflater.from(context); 25 mDatas = datas; 26 } 27 28 //返回数据集的长度 29 @Override 30 public int getCount() { 31 return mDatas.size(); 32 } 33 34 @Override 35 public Object getItem(int position) { 36 return mDatas.get(position); 37 } 38 39 @Override 40 public long getItemId(int position) { 41 return position; 42 } 43 44 //这个方法才是重点，我们要为它编写一个ViewHolder 45 @Override 46 public View getView(int position, View convertView, ViewGroup parent) { 47 ViewHolder holder = null; 48 if (convertView == null) { 49 convertView = mInflater.inflate(R.layout.item_listview, parent, false); //加载布局 50 holder = new ViewHolder(); 51 52 holder.titleTv = (TextView) convertView.findViewById(R.id.titleTv); 53 holder.descTv = (TextView) convertView.findViewById(R.id.descTv); 54 holder.timeTv = (TextView) convertView.findViewById(R.id.timeTv); 55 holder.phoneTv = (TextView) convertView.findViewById(R.id.phoneTv); 56 57 convertView.setTag(holder); 58 } else { //else里面说明，convertView已经被复用了，说明convertView中已经设置过tag了，即holder 59 holder = (ViewHolder) convertView.getTag(); 60 } 61 62 Bean bean = mDatas.get(position); 63 holder.titleTv.setText(bean.getTitle()); 64 holder.descTv.setText(bean.getDesc()); 65 holder.timeTv.setText(bean.getTime()); 66 holder.phoneTv.setText(bean.getPhone()); 67 68 return convertView; 69 } 70 71 //这个ViewHolder只能服务于当前这个特定的adapter，因为ViewHolder里会指定item的控件，不同的ListView，item可能不同，所以ViewHolder写成一个私有的类 72 private class ViewHolder { 73 TextView titleTv; 74 TextView descTv; 75 TextView timeTv; 76 TextView phoneTv; 77 } 78 79 }
(5)MainActivity.java:
1 package com.smyhvae.baseadapter; 2 3 import android.app.Activity; 4 import android.os.Bundle; 5 import android.view.Menu; 6 import android.view.MenuItem; 7 import android.widget.ListView; 8 9 import com.smyhvae.baseadapter.entities.Bean; 10 11 import java.util.ArrayList; 12 import java.util.List; 13 14 public class MainActivity extends Activity { 15 16 private ListView listView; 17 private List<Bean> mDatas; 18 private MyAdapter mAdapter; 19 20 @Override 21 protected void onCreate(Bundle savedInstanceState) { 22 super.onCreate(savedInstanceState); 23 setContentView(R.layout.activity_main); 24 25 initView(); 26 initData(); 27 28 } 29 30 //方法：初始化View 31 private void initView() { 32 listView = (ListView) findViewById(R.id.listView); 33 } 34 35 //方法；初始化Data 36 private void initData() { 37 mDatas = new ArrayList<Bean>(); 38 39 //将数据装到集合中去 40 Bean bean = new Bean("Android新技能1", "Android为ListView和GridView打造万能适配器", "2015-05-04", "10086"); 41 mDatas.add(bean); 42 43 bean = new Bean("Android新技能2", "Android为ListView和GridView打造万能适配器", "2015-05-04", "10086"); 44 mDatas.add(bean); 45 46 bean = new Bean("Android新技能3", "Android为ListView和GridView打造万能适配器", "2015-05-04", "10086"); 47 mDatas.add(bean); 48 49 bean = new Bean("Android新技能4", "Android为ListView和GridView打造万能适配器", "2015-05-04", "10086"); 50 mDatas.add(bean); 51 52 //为数据绑定适配器 53 mAdapter = new MyAdapter(this,mDatas); 54 55 listView.setAdapter(mAdapter); 56 } 57 58 }
运行效果如下：
【工程文件】
2015-05-04-BaseAdapter的传统写法.rar
二、ListView中自定义adapter的封装（万能的写法来编写适配器）：
完整版代码如下：
(1)activity_main.xml:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent"> <ListView android:id="@+id/listView" android:layout_width="match_parent" android:layout_height="match_parent"></ListView> </RelativeLayout>
（2）item_listview.xml.xml:（ListView中单个item的布局）
1 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 2 xmlns:tools="http://schemas.android.com/tools" 3 android:layout_width="match_parent" 4 android:layout_height="match_parent" 5 android:padding="10dp"> 6 7 <TextView 8 android:id="@+id/titleTv" 9 android:layout_width="wrap_content" 10 android:layout_height="wrap_content" 11 android:singleLine="true" 12 android:text="Android新技能" 13 android:textColor="#444" 14 android:textSize="16sp" /> 15 16 <TextView 17 android:id="@+id/descTv" 18 android:layout_width="match_parent" 19 android:layout_height="wrap_content" 20 android:layout_below="@+id/titleTv" 21 android:layout_marginTop="10dp" 22 android:maxLines="2" 23 android:minLines="1" 24 android:text="Android为ListView和GridView打造万能适配器" 25 android:textColor="#898989" 26 android:textSize="16sp" /> 27 28 <TextView 29 android:id="@+id/timeTv" 30 android:paddingTop="3dp" 31 android:layout_width="wrap_content" 32 android:layout_height="wrap_content" 33 android:layout_below="@+id/descTv" 34 android:layout_marginTop="10dp" 35 android:text="2015-05-04" 36 android:textColor="#898989" 37 android:textSize="12sp" /> 38 39 <TextView 40 android:padding="2dp" 41 android:id="@+id/phoneTv" 42 android:gravity="center" 43 android:layout_width="wrap_content" 44 android:layout_height="wrap_content" 45 android:layout_below="@+id/descTv" 46 android:layout_marginTop="10dp" 47 android:background="#2ED667" 48 android:drawableLeft="@mipmap/phone" 49 android:drawablePadding="5dp" 50 android:text="10086" 51 android:textColor="#ffffff" 52 android:textSize="12sp" 53 android:layout_alignParentRight="true" /> 54 55 56 </RelativeLayout>
其对应的布局效果如下：
（3）Bean.java:数据集
1 package com.smyhvae.baseadapter.entities; 2 3 /** 4 * Created by smyhvae on 2015/5/4. 5 */ 6 public class Bean { 7 private String title; 8 private String desc; 9 private String time; 10 private String phone; 11 12 public Bean() { 13 } 14 15 public Bean(String title, String desc, String time, String phone) { 16 this.title = title; 17 18 this.desc = desc; 19 this.time = time; 20 this.phone = phone; 21 } 22 23 public String getTitle() { 24 return title; 25 } 26 27 public void setTitle(String title) { 28 this.title = title; 29 } 30 31 public String getDesc() { 32 return desc; 33 } 34 35 public void setDesc(String desc) { 36 this.desc = desc; 37 } 38 39 public String getTime() { 40 return time; 41 } 42 43 public void setTime(String time) { 44 this.time = time; 45 } 46 47 public String getPhone() { 48 return phone; 49 } 50 51 public void setPhone(String phone) { 52 this.phone = phone; 53 } 54 }
（4）【可复用的代码】ViewHolder.java:
1 package com.smyhvae.baseadapter.utils; 2 3 import android.content.Context; 4 import android.util.SparseArray; 5 import android.view.LayoutInflater; 6 import android.view.View; 7 import android.view.ViewGroup; 8 9 /** 10 * Created by smyhvae on 2015/5/4. 11 */ 12 public class ViewHolder { 13 14 private SparseArray<View> mViews; 15 private int mPosition; 16 private View mConvertView; 17 18 public ViewHolder(Context context, ViewGroup parent, int layoutId, int position) { 19 this.mPosition = position; 20 this.mViews = new SparseArray<View>(); 21 22 mConvertView = LayoutInflater.from(context).inflate(layoutId, parent, false); 23 24 mConvertView.setTag(this); 25 26 } 27 28 public static ViewHolder get(Context context, View convertView, ViewGroup parent, int layoutId, int position) { 29 if (convertView == null) { 30 return new ViewHolder(context, parent, layoutId, position); 31 } else { 32 ViewHolder holder = (ViewHolder) convertView.getTag(); 33 holder.mPosition = position; //即时ViewHolder是复用的，但是position记得更新一下 34 return holder; 35 } 36 } 37 38 /* 39 通过viewId获取控件 40 */ 41 //使用的是泛型T,返回的是View的子类 42 public <T extends View> T getView(int viewId) { 43 View view = mViews.get(viewId); 44 45 if (view == null) { 46 view = mConvertView.findViewById(viewId); 47 mViews.put(viewId, view); 48 } 49 50 return (T) view; 51 } 52 53 public View getConvertView() { 54 return mConvertView; 55 } 56 57 }
（5）【可复用的代码】ListViewAdapter.java:自定义的通用适配器，继承自BaseAdapter。以后如果是自定义ListView的adapter，继承它就行了
1 package com.smyhvae.baseadapter.utils; 2 3 import android.content.Context; 4 import android.view.LayoutInflater; 5 import android.view.View; 6 import android.view.ViewGroup; 7 import android.widget.BaseAdapter; 8 9 import java.util.List; 10 11 /** 12 * Created by smyhvae on 2015/5/4. 13 * 通用的ListView的BaseAdapter，所有的ListView的自定义adapter都可以继承这个类哦 14 */ 15 public abstract class ListViewAdapter<T> extends BaseAdapter { 16 17 //为了让子类访问，于是将属性设置为protected 18 protected Context mContext; 19 protected List<T> mDatas; 20 protected LayoutInflater mInflater; 21 private int layoutId; //不同的ListView的item布局肯能不同，所以要把布局单独提取出来 22 23 public ListViewAdapter(Context context, List<T> datas, int layoutId) { 24 this.mContext = context; 25 mInflater = LayoutInflater.from(context); 26 this.mDatas = datas; 27 this.layoutId = layoutId; 28 } 29 30 @Override 31 public int getCount() { 32 return mDatas.size(); 33 } 34 35 @Override 36 public T getItem(int position) { 37 return mDatas.get(position); 38 } 39 40 @Override 41 public long getItemId(int position) { 42 return position; 43 } 44 45 @Override 46 public View getView(int position, View convertView, ViewGroup parent) { 47 //初始化ViewHolder,使用通用的ViewHolder，一样代码就搞定ViewHolder的初始化咯 48 ViewHolder holder = ViewHolder.get(mContext, convertView, parent, layoutId, position);//layoutId就是单个item的布局 49 50 convert(holder, getItem(position)); 51 return holder.getConvertView(); //这一行的代码要注意了 52 } 53 54 //将convert方法公布出去 55 public abstract void convert(ViewHolder holder, T t); 56 57 }
（6）ListViewAdapterWithViewHolder.java:继承自ListViewAdapter
1 package com.smyhvae.baseadapter; 2 3 import android.content.Context; 4 import android.widget.TextView; 5 6 import com.smyhvae.baseadapter.entities.Bean; 7 import com.smyhvae.baseadapter.utils.ListViewAdapter; 8 import com.smyhvae.baseadapter.utils.ViewHolder; 9 10 import java.util.List; 11 12 /** 13 * Created by smyhvae on 2015/5/4. 14 */ 15 public class ListViewAdapterWithViewHolder extends ListViewAdapter<Bean> { 16 17 //MyAdapter需要一个Context，通过Context获得Layout.inflater，然后通过inflater加载item的布局 18 public ListViewAdapterWithViewHolder(Context context, List<Bean> datas) { 19 super(context, datas, R.layout.item_listview); 20 } 21 22 @Override 23 public void convert(ViewHolder holder, Bean bean) { 24 25 ((TextView) holder.getView(R.id.titleTv)).setText(bean.getTitle()); 26 ((TextView) holder.getView(R.id.descTv)).setText(bean.getDesc()); 27 ((TextView) holder.getView(R.id.timeTv)).setText(bean.getTime()); 28 ((TextView) holder.getView(R.id.phoneTv)).setText(bean.getPhone()); 29 30 /* 31 TextView tv = holder.getView(R.id.titleTv); 32 tv.setText(...); 33 34 ImageView view = getView(viewId); 35 Imageloader.getInstance().loadImag(view.url); 36 */ 37 } 38 }
（7）MainActivity.java:
1 package com.smyhvae.baseadapter; 2 3 import android.app.Activity; 4 import android.os.Bundle; 5 import android.widget.ListView; 6 7 import com.smyhvae.baseadapter.entities.Bean; 8 9 import java.util.ArrayList; 10 import java.util.List; 11 12 public class MainActivity extends Activity { 13 14 private ListView listView; 15 private List<Bean> mDatas; 16 17 private ListViewAdapterWithViewHolder listViewAdapterWithViewHolder; 18 19 @Override 20 protected void onCreate(Bundle savedInstanceState) { 21 super.onCreate(savedInstanceState); 22 setContentView(R.layout.activity_main); 23 24 initView(); 25 initData(); 26 } 27 28 29 //方法：初始化View 30 private void initView() { 31 listView = (ListView) findViewById(R.id.listView); 32 } 33 34 //方法；初始化Data 35 private void initData() { 36 mDatas = new ArrayList<Bean>(); 37 38 //将数据装到集合中去 39 Bean bean = new Bean("Android新技能1", "Android为ListView和GridView打造万能适配器", "2015-05-04", "10086"); 40 mDatas.add(bean); 41 42 bean = new Bean("Android新技能2", "Android为ListView和GridView打造万能适配器", "2015-05-04", "10086"); 43 mDatas.add(bean); 44 45 bean = new Bean("Android新技能3", "Android为ListView和GridView打造万能适配器", "2015-05-04", "10086"); 46 mDatas.add(bean); 47 48 bean = new Bean("Android新技能4", "Android为ListView和GridView打造万能适配器", "2015-05-04", "10086"); 49 mDatas.add(bean); 50 51 //为数据绑定适配器 52 listViewAdapterWithViewHolder = new ListViewAdapterWithViewHolder(this, mDatas); 53 54 listView.setAdapter(listViewAdapterWithViewHolder); 55 56 } 57 }
运行效果：
这样的话，以后每写个ListView，就这么做：直接导入ViewHolder.java和ListViewAdapter，然后写一个自定义adapter继承自ListViewAdapter就行了。
【工程文件】
三、常见问题：
1、item控件抢占焦点：
假设item里有一个checkbox，那运行程序之后，发现只有checkBox能被点击，而item中的其他位置不能被点击(包括点击整个item也没有反应)，这是由于checkbox抢占了整个item的焦点。办法是:：
办法1：为该checkBox设置属性：
android:focusable = "false"
办法二：为该item设置属性：
android:descendantFocusability = "blocksDescendants" 不让这个item的焦点从上往下传。
2、ListView复用导致内容错乱。