Android开发中ListView自定义adapter的封装

【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 

<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"
 android:padding="10dp">
 <TextView
 android:id="@+id/titleTv"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:singleLine="true"
 android:text="Android新技能"
 android:textColor="#444"
 android:textSize="16sp" />
 <TextView
 android:id="@+id/descTv"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_below="@+id/titleTv"
 android:layout_marginTop="10dp"
 android:maxLines="2"
 android:minLines="1"
 android:text="Android为ListView和GridView打造万能适配器"
 android:textColor="#898989"
 android:textSize="16sp" />
 <TextView
 android:id="@+id/timeTv"
 android:paddingTop="3Dp"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:layout_below="@+id/descTv"
 android:layout_marginTop="10dp"
 android:text="2015-05-04"
 android:textColor="#898989"
 android:textSize="12sp" />
 <TextView
 android:padding="2dp"
 android:id="@+id/phoneTv"
 android:gravity="center"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:layout_below="@+id/descTv"
 android:layout_marginTop="10dp"
 android:background="#2ED667"
 android:drawableLeft="@mipmap/phone"
 android:drawablePadding="5dp"
 android:text="10086"
 android:textColor="#ffffff"
 android:textSize="12sp"
 android:layout_alignParentRight="true" />
</RelativeLayout>

其对应的布局效果如下：

（3）Bean.java:ListView的数据集

package com.smyhvae.baseadapter.entities;

public class Bean {
 private String title;
 private String desc;
 private String time;
 private String phone;
 public Bean() {
 }
 public Bean(String title, String desc, String time, String phone) {
 this.title = title;
 this.desc = desc;
 this.time = time;
 this.phone = phone;
 }
 public String getTitle() {
 return title;
 }
 public void setTitle(String title) {
 this.title = title;
 }
 public String getDesc() {
 return desc;
 }
 public void setDesc(String desc) {
 this.desc = desc;
 }
 public String getTime() {
 return time;
 }
 public void setTime(String time) {
 this.time = time;
 }
 public String getPhone() {
 return phone;
 }
 public void setPhone(String phone) {
 this.phone = phone;
 }
}

（4）MyAdapter.java:自定义适配器，继承自BaseAdapter 

package com.smyhvae.baseadapter;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;
import com.smyhvae.baseadapter.entities.Bean;
import java.util.List;

public class MyAdapter extends BaseAdapter {
 private LayoutInflater mInflater;
 private List<Bean> mDatas;
 //MyAdapter需要一个Context，通过Context获得Layout.inflater，然后通过inflater加载item的布局
 public MyAdapter(Context context, List<Bean> datas) {
 mInflater = LayoutInflater.from(context);
 mDatas = datas;
 }
 //返回数据集的长度
 @Override
 public int getCount() {
 return mDatas.size();
 }
 @Override
 public Object getItem(int position) {
 return mDatas.get(position);
 }
 @Override
 public long getItemId(int position) {
 return position;
 }
 //这个方法才是重点，我们要为它编写一个ViewHolder
 @Override
 public View getView(int position, View convertView, ViewGroup parent) {
 ViewHolder holder = null;
 if (convertView == null) {
  convertView = mInflater.inflate(R.layout.item_listview, parent, false); //加载布局
  holder = new ViewHolder();
  holder.titleTv = (TextView) convertView.findViewById(R.id.titleTv);
  holder.descTv = (TextView) convertView.findViewById(R.id.descTv);
  holder.timeTv = (TextView) convertView.findViewById(R.id.timeTv);
  holder.phoneTv = (TextView) convertView.findViewById(R.id.phoneTv);
  convertView.setTag(holder);
 } 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
  holder = (ViewHolder) convertView.getTag();
 }
 Bean bean = mDatas.get(position);
 holder.titleTv.setText(bean.getTitle());
 holder.descTv.setText(bean.getDesc());
 holder.timeTv.setText(bean.getTime());
 holder.phoneTv.setText(bean.getPhone());
 return convertView;
 }
 //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
 private class ViewHolder {
 TextView titleTv;
 TextView descTv;
 TextView timeTv;
 TextView phoneTv;
 }
}

(5)MainActivity.java: 

package com.smyhvae.baseadapter;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ListView;
import com.smyhvae.baseadapter.entities.Bean;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends Activity {
 private ListView listView;
 private List<Bean> mDatas;
 private MyAdapter mAdapter;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 initView();
 initData();
 }
 //方法：初始化View
 private void initView() {
 listView = (ListView) findViewById(R.id.listView);
 }
 //方法；初始化Data
 private void initData() {
 mDatas = new ArrayList<Bean>();
 //将数据装到集合中去
 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");
 mDatas.add(bean);
 bean = new Bean("Android新技能2", "Android为ListView和GridView打造万能适配器", "2015-05-04", "10086");
 mDatas.add(bean);
 bean = new Bean("Android新技能3", "Android为ListView和GridView打造万能适配器", "2015-05-04", "10086");
 mDatas.add(bean);
 bean = new Bean("Android新技能4", "Android为ListView和GridView打造万能适配器", "2015-05-04", "10086");
 mDatas.add(bean);
 //为数据绑定适配器
 mAdapter = new MyAdapter(this,mDatas);
 listView.setAdapter(mAdapter);
 }
}

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） 

<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"
 android:padding="10dp">
 <TextView
 android:id="@+id/titleTv"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:singleLine="true"
 android:text="Android新技能"
 android:textColor="#444"
 android:textSize="16sp" />
 <TextView
 android:id="@+id/descTv"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_below="@+id/titleTv"
 android:layout_marginTop="10dp"
 android:maxLines="2"
 android:minLines="1"
 android:text="Android为ListView和GridView打造万能适配器"
 android:textColor="#898989"
 android:textSize="16sp" />
 <TextView
 android:id="@+id/timeTv"
 android:paddingTop="3dp"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:layout_below="@+id/descTv"
 android:layout_marginTop="10dp"
 android:text="2015-05-04"
 android:textColor="#898989"
 android:textSize="12sp" />
 <TextView
 android:padding="2dp"
 android:id="@+id/phoneTv"
 android:gravity="center"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:layout_below="@+id/descTv"
 android:layout_marginTop="10dp"
 android:background="#2ED667"
 android:drawableLeft="@mipmap/phone"
 android:drawablePadding="5dp"
 android:text="10086"
 android:textColor="#ffffff"
 android:textSize="12sp"
 android:layout_alignParentRight="true" />
</RelativeLayout>

其对应的布局效果如下：

 

（3）Bean.java:数据集 

package com.smyhvae.baseadapter.entities;

public class Bean {
 private String title;
 private String desc;
 private String time;
 private String phone;
 public Bean() {
 }
 public Bean(String title, String desc, String time, String phone) {
 this.title = title;
 this.desc = desc;
 this.time = time;
 this.phone = phone;
 }
 public String getTitle() {
 return title;
 }
 public void setTitle(String title) {
 this.title = title;
 }
 public String getDesc() {
 return desc;
 }
 public void setDesc(String desc) {
 this.desc = desc;
 }
 public String getTime() {
 return time;
 }
 public void setTime(String time) {
 this.time = time;
 }
 public String getPhone() {
 return phone;
 }
 public void setPhone(String phone) {
 this.phone = phone;
 }
}

（4）【可复用的代码】ViewHolder.java: 

package com.smyhvae.baseadapter.utils;
import android.content.Context;
import android.util.SparseArray;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class ViewHolder {
 private SparseArray<View> mViews;
 private int mPosition;
 private View mConvertView;
 public ViewHolder(Context context, ViewGroup parent, int layoutId, int position) {
 this.mPosition = position;
 this.mViews = new SparseArray<View>();
 mConvertView = LayoutInflater.from(context).inflate(layoutId, parent, false);
 mConvertView.setTag(this);
 }
 public static ViewHolder get(Context context, View convertView, ViewGroup parent, int layoutId, int position) {
 if (convertView == null) {
  return new ViewHolder(context, parent, layoutId, position);
 } else {
  ViewHolder holder = (ViewHolder) convertView.getTag();
  holder.mPosition = position; //即使ViewHolder是复用的，但是position记得更新一下
  return holder;
 }
 }
 
 //使用的是泛型T,返回的是View的子类
 public <T extends View> T getView(int viewId) {
 View view = mViews.get(viewId);
 if (view == null) {
  view = mConvertView.findViewById(viewId);
  mViews.put(viewId, view);
 }
 return (T) view;
 }
 public View getConvertView() {
 return mConvertView;
 }
}

（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 

package com.smyhvae.baseadapter.utils;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import java.util.List;

public abstract class ListViewAdapter<T> extends BaseAdapter {
 //为了让子类访问，于是将属性设置为protected
 protected Context mContext;
 protected List<T> mDatas;
 protected LayoutInflater mInflater;
 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
 public ListViewAdapter(Context context, List<T> datas, int layoutId) {
 this.mContext = context;
 mInflater = LayoutInflater.from(context);
 this.mDatas = datas;
 this.layoutId = layoutId;
 }
 @Override
 public int getCount() {
 return mDatas.size();
 }
 @Override
 public T getItem(int position) {
 return mDatas.get(position);
 }
 @Override
 public long getItemId(int position) {
 return position;
 }
 @Override
 public View getView(int position, View convertView, ViewGroup parent) {
 //初始化ViewHolder,使用通用的ViewHolder，一行代码就搞定ViewHolder的初始化咯
 ViewHolder holder = ViewHolder.get(mContext, convertView, parent, layoutId, position);//layoutId就是单个item的布局
 convert(holder, getItem(position));
 return holder.getConvertView(); //这一行的代码要注意了
 }
 //将convert方法公布出去
 public abstract void convert(ViewHolder holder, T t);
}

（6）ListViewAdapterWithViewHolder.java:继承自ListViewAdapter 

package com.smyhvae.baseadapter;
import android.content.Context;
import android.widget.TextView;
import com.smyhvae.baseadapter.entities.Bean;
import com.smyhvae.baseadapter.utils.ListViewAdapter;
import com.smyhvae.baseadapter.utils.ViewHolder;
import java.util.List;

public class ListViewAdapterWithViewHolder extends ListViewAdapter<Bean> {
 //MyAdapter需要一个Context，通过Context获得Layout.inflater，然后通过inflater加载item的布局
 public ListViewAdapterWithViewHolder(Context context, List<Bean> datas) {
 super(context, datas, R.layout.item_listview);
 }
 @Override
 public void convert(ViewHolder holder, Bean bean) {
 ((TextView) holder.getView(R.id.titleTv)).setText(bean.getTitle());
 ((TextView) holder.getView(R.id.descTv)).setText(bean.getDesc());
 ((TextView) holder.getView(R.id.timeTv)).setText(bean.getTime());
 ((TextView) holder.getView(R.id.phoneTv)).setText(bean.getPhone());

 }
}

（7）MainActivity.java: 

package com.smyhvae.baseadapter;
import android.app.Activity;
import android.os.Bundle;
import android.widget.ListView;
import com.smyhvae.baseadapter.entities.Bean;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends Activity {
 private ListView listView;
 private List<Bean> mDatas;
 private ListViewAdapterWithViewHolder listViewAdapterWithViewHolder;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 initView();
 initData();
 }
 //方法：初始化View
 private void initView() {
 listView = (ListView) findViewById(R.id.listView);
 }
 //方法；初始化Data
 private void initData() {
 mDatas = new ArrayList<Bean>();
 //将数据装到集合中去
 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");
 mDatas.add(bean);
 bean = new Bean("Android新技能2", "Android为ListView和GridView打造万能适配器", "2015-05-04", "10086");
 mDatas.add(bean);
 bean = new Bean("Android新技能3", "Android为ListView和GridView打造万能适配器", "2015-05-04", "10086");
 mDatas.add(bean);
 bean = new Bean("Android新技能4", "Android为ListView和GridView打造万能适配器", "2015-05-04", "10086");
 mDatas.add(bean);
 //为数据绑定适配器
 listViewAdapterWithViewHolder = new ListViewAdapterWithViewHolder(this, mDatas);
 listView.setAdapter(listViewAdapterWithViewHolder);
 }
}

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】2015-05-04-BaseAdapter的封装.rar

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2：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。

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