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1.概述

Adapter写多了就想"偷懒"于是封装了一个通用的Adapter,话不多说上Demo先:https://github.com/zh-xiao/CommonListView.git

2.举个栗子

传统的listview写法:

layout:

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.xiao.commonlistview.MainActivity">

    <ListView
        android:id="@+id/lv"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
</RelativeLayout>

item_layout:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="match_parent"
              android:layout_height="50dp"
              android:orientation="horizontal">

    <ImageView
        android:id="@+id/head_img"
        android:layout_width="50dp"
        android:layout_height="match_parent"/>

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:orientation="vertical">
        <TextView
            android:id="@+id/name"
            android:layout_width="wrap_content"
            android:layout_height="0dp"
            android:layout_weight="1"/>
        <TextView
            android:id="@+id/phone_number"
            android:layout_width="wrap_content"
            android:layout_height="0dp"
            android:layout_weight="1"/>
    </LinearLayout>

</LinearLayout>

bean:

public class ContactsBean {
    private String name;
    private String phoneNumber;
    private String head_img;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPhoneNumber() {
        return phoneNumber;
    }

    public void setPhoneNumber(String phoneNumber) {
        this.phoneNumber = phoneNumber;
    }

    public String getHead_img() {
        return head_img;
    }

    public void setHead_img(String head_img) {
        this.head_img = head_img;
    }
}

adapter:

public class ContactsAdapter extends BaseAdapter{

    private Context mContext;
    private List<ContactsBean> mList;

    public ContactsAdapter(Context context, List<ContactsBean> list) {
        mContext = context;
        mList = list;
    }

    @Override
    public int getCount() {
        return mList.size();
    }

    @Override
    public Object getItem(int position) {
        return mList.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder;
        if (null==convertView){
            convertView= LayoutInflater.from(mContext).inflate(R.layout.item_layout,parent,false);
            holder=new ViewHolder();
            holder.name= (TextView) convertView.findViewById(R.id.name);
            holder.phoneNumber= (TextView) convertView.findViewById(R.id.phone_number);
            holder.headImg= (ImageView) convertView.findViewById(R.id.head_img);
            convertView.setTag(holder);
        }else {
            holder= (ViewHolder) convertView.getTag();
        }
        ContactsBean contactsBean = mList.get(position);
        holder.name.setText(contactsBean.getName());
        holder.phoneNumber.setText(contactsBean.getPhoneNumber());
        Picasso.with(mContext).load(contactsBean.getHead_img()).into(holder.headImg);
        return convertView;
    }

    class ViewHolder{
        TextView name;
        TextView phoneNumber;
        ImageView headImg;
    }

}

activity:

public class MainActivity extends AppCompatActivity {
    private List<ContactsBean> mList=new ArrayList<>();
    private ContactsAdapter mAdapter;
    private android.widget.ListView lv;
    private android.widget.RelativeLayout activitymain;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        this.activitymain = (RelativeLayout) findViewById(R.id.activity_main);
        this.lv = (ListView) findViewById(R.id.lv);
        lv.setAdapter(mAdapter=new ContactsAdapter(this,mList));
        initData();
    }

    public void initData(){
        for (int i=0;i<20;i++){
            ContactsBean bean=new ContactsBean();
            bean.setName("小明");
            bean.setPhoneNumber("110");
            bean.setHead_img("http://img.qqai.net/uploads/i_2_1826721258x2403292640_21.jpg");
            mList.add(bean);
        }
        mAdapter.notifyDataSetChanged();
    }
}

现在我们分析一下传统的写法

既然我们要造一个通用的adapter,那分析一下adapter先:
1.从构造方法到getItemId方法都是一样的写法,也就bean不一样(这部分用一个泛型就可以封装起来).
2.再看getView方法,convertView通过setTag绑定了ViewHolder,而Viewholder又通过findviewById保存了convertView里所有的控件,那我们就可以写一个通用的ViewHolder类,包含两个成员变量mConvertView和mViewMap.mConvertView通过setTag绑定ViewHolder,mViewMap通过<Id,View>键值对保存mConvertView里所有的控件.
OK,思路理清了,开始写代码

通用ViewHolder

public class ViewHolder {
    private View mConvertView;
    private Map<Integer,View> mViewMap;
    private Context mContext;

    public ViewHolder(Context context,int layoutId,ViewGroup parent){
        mConvertView= LayoutInflater.from(context).inflate(layoutId,parent,false);
        mViewMap=new HashMap<>();
        mConvertView.setTag(this);
        mContext=context;
    }

    public synchronized static ViewHolder getHolder(Context context,int layoutId, View convertView, ViewGroup parent){
        if (null==convertView){
            return new ViewHolder(context,layoutId,parent);
        }else{
            return (ViewHolder) convertView.getTag();
        }
    }

    public View getConvertView(){
        return mConvertView;
    }

    /**
     * 获取控件,mViewMap里有则直接取,没有则通过findViewById拿到并保存到mViewMap
     * @param viewId 控件id
     * @param <T>
     * @return
     */
    public <T extends View> T getView(int viewId){
        if (mViewMap.containsKey(viewId)){
            return (T) mViewMap.get(viewId);
        }else{
            View view=mConvertView.findViewById(viewId);
            mViewMap.put(viewId,view);
            return (T) view;
        }
    }

    /**
     * 内容适配,一般就用到ImageView和TextView,而且ImageView通常是url,所以就用反射封装一下,返回自身实现链式调用
     * @param viewId 控件id
     * @param content 要适配的内容(文字字符串/图片url)
     * @return
     */
    public ViewHolder set(int viewId,String content){
        View view=getView(viewId);
        if (view instanceof TextView){
            ((TextView) view).setText(content);
        }else if (view instanceof ImageView){
            Picasso.with(mContext).load(content).into((ImageView) view);
        }
        return this;
    }
}

通用adapter

public abstract class CommonAdapter<T> extends BaseAdapter {

    protected Context mContext;
    protected List<T> mList;
    protected int mLayoutId;

    public CommonAdapter(Context context, List<T> list, int layoutId) {
        mContext=context;
        mList=list;
        mLayoutId=layoutId;
    }

    @Override
    public int getCount() {
        return mList.size();
    }

    @Override
    public T getItem(int position) {
        return mList.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    /**
     * 根据OO思想,第一行和最后一行不存在变化,所以封装起来,中间适配内容的部分通过convertView抽象方法交给调用者去实现
     * @param position
     * @param convertView
     * @param parent
     * @return
     */
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder = ViewHolder.getHolder(mContext, mLayoutId, convertView, parent);
        convertView(holder,mList.get(position));
        return holder.getConvertView();
    }

    /**
     * 真正内容适配的方法
     * @param holder
     * @param t
     */
    public abstract void convertView(ViewHolder holder,T t);
}

造轮子的工作就over了,看下现在的listView写法
layout,item_layout,bean不变
adapter由commonAdapter替代
直接看adcitivity:

public class MainActivity extends AppCompatActivity {
    private List<ContactsBean> mList = new ArrayList<>();
    //    private ContactsAdapter mAdapter;
    private CommonAdapter mAdapter;
    private android.widget.ListView lv;
    private android.widget.RelativeLayout activitymain;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        this.activitymain = (RelativeLayout) findViewById(R.id.activity_main);
        this.lv = (ListView) findViewById(R.id.lv);
//        lv.setAdapter(mAdapter=new ContactsAdapter(this,mList));
        lv.setAdapter(mAdapter = new CommonAdapter<ContactsBean>(this, mList, R.layout.item_layout) {
            @Override
            public void convertView(ViewHolder holder, ContactsBean contactsBean) {
                holder.set(R.id.name, contactsBean.getName())
                        .set(R.id.phone_number, contactsBean.getPhoneNumber())
                        .set(R.id.head_img, contactsBean.getHead_img());
            }
        });
        initData();
    }

    public void initData() {
        for (int i = 0; i < 20; i++) {
            ContactsBean bean = new ContactsBean();
            bean.setName("小明");
            bean.setPhoneNumber("110");
            bean.setHead_img("http://img.qqai.net/uploads/i_2_1826721258x2403292640_21.jpg");
            mList.add(bean);
        }
        mAdapter.notifyDataSetChanged();
    }
}

是不是超简单,以后只需要一个匿名内部类就OK了.O(∩_∩)O.

参考:http://blog.csdn.net/lmj623565791/article/details/38902805