Android开发笔记之Adapter用法

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Adapter的概念

适配器对象作为视图和该视图的基础数据之间的桥梁。适配器提供对数据项的访问。适配器还负责对数据集中的每个项目进行视图的视图。

三个要素：

Data—连接—Adapter—连接—View

Adapter接口的继承关系如下图：

重写 getView（）方法的工作原理：

1.ListView 向 Adapter 对于List中的每一条数据索要一个View ，“give me a view” （getView)。

2.一个新的View 返回并且展示。

但是出现下面的情况，系统内存无法满足，*ListView里面的条目过多，例如，100000万条。其中只有可见的项目存在内存中，其他的在Recycler中。其实我的理解Recyler就是一个队列，用来存储不在屏幕范围内的item，如果item滚出屏幕范围，那么就入队，这里的滚出是完全滚出，即边界等也要完全滚出。如果新的item要滚进来，那么android系统的framework就会查看Recyler是否含有可以重复使用的iew，如果有那么就重新设置该iew 的数据源，然后显示，即出队。

常用的Adapter实现的类有：

（1）ArrayAdapter，支持泛型，可以展示一行字符串。

ArrayAdapterDemo：

使用系统自带的android.R.layout.simple_list_item_1布局文件。

MainActivity.java文件

package edu.jnu.adapterdemo;import android.app.Activity;import android.content.Context;import android.net.Uri;import android.os.Bundle;import android.support.design.widget.FloatingActionButton;import android.support.design.widget.Snackbar;import android.support.v7.app.AppCompatActivity;import android.support.v7.widget.Toolbar;import android.util.Log;import android.view.View;import android.view.Menu;import android.view.MenuItem;import android.view.ViewGroup;import android.widget.AdapterView;import android.widget.ArrayAdapter;import android.widget.BaseAdapter;import android.widget.ListView;import android.widget.SimpleAdapter;import android.widget.TextView;import android.widget.Toast;import com.google.android.gms.appindexing.Action;import com.google.android.gms.appindexing.AppIndex;import com.google.android.gms.common.api.GoogleApiClient;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;public class MainActivity extends Activity {    private ListView listView;    private List<String> list;    private ArrayAdapter arrayAdapter;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        listView = (ListView) findViewById(R.id.listView);        list = new ArrayList<String>();        for (int i = 1; i < 100; i++) {            list.add("item" + i);        }        arrayAdapter = new ArrayAdapter(this,android.R.layout.simple_list_item_1,list);        listView.setAdapter(arrayAdapter);    }}

（2).SimpleAdapter可以添加各种各样的组件，灵活易用。

lv_layout.xml文件

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="horizontal" android:layout_width="fill_parent"    android:layout_height="fill_parent">    <ImageView        android:id="@+id/img"        android:layout_width="60dp"        android:layout_height="60dp"        android:layout_margin="5dp"        />    <LinearLayout        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:orientation="vertical"        >        <TextView            android:id="@+id/text1"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:textSize="22sp"            />        <TextView            android:id="@+id/text2"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:textSize="12sp"/>    </LinearLayout></LinearLayout>

MainActivity.java文件

package edu.jnu.adapterdemo;import android.app.Activity;import android.content.Context;import android.net.Uri;import android.os.Bundle;import android.support.design.widget.FloatingActionButton;import android.support.design.widget.Snackbar;import android.support.v7.app.AppCompatActivity;import android.support.v7.widget.Toolbar;import android.util.Log;import android.view.View;import android.view.Menu;import android.view.MenuItem;import android.view.ViewGroup;import android.widget.AdapterView;import android.widget.ArrayAdapter;import android.widget.BaseAdapter;import android.widget.ListView;import android.widget.SimpleAdapter;import android.widget.TextView;import android.widget.Toast;import com.google.android.gms.appindexing.Action;import com.google.android.gms.appindexing.AppIndex;import com.google.android.gms.common.api.GoogleApiClient;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;public class MainActivity extends Activity implements AdapterView.OnItemClickListener {    private ListView listView;    private List<String> list;    private SimpleAdapter simpleAdapter;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        listView = (ListView) findViewById(R.id.listView);        list = new ArrayList<String>();        for (int i = 1; i < 100; i++) {            list.add("item" + i);        }        simpleAdapter = new SimpleAdapter(this,getdata(),R.layout.lv_layout,                new String[]{"title","info","image"},                new int[]{R.id.text1,R.id.text2,R.id.img});        listView.setAdapter(simpleAdapter);        listView.setOnItemClickListener(this);    }    private List<Map<String,Object>> getdata(){        List<Map<String,Object>> list = new ArrayList<Map<String,Object>>();        Map<String,Object> map = new HashMap<String,Object>();        map.put("title","Title1");        map.put("info","Info1");        map.put("image",R.drawable.i1);        list.add(map);        map = new HashMap<String,Object>();        map.put("title","Title2");        map.put("info","Info2");        map.put("image",R.drawable.i1);        list.add(map);        map = new HashMap<String,Object>();        map.put("title","Title3");        map.put("info","Info3");        map.put("image",R.drawable.i1);        list.add(map);        return list;    }    @Override    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {        Toast.makeText(this,"pos:"+position,Toast.LENGTH_SHORT).show();    }}

（3).BaseAdapter：可以对ListView的性能进行优化，通过重写GetView方法。

采用ViewHolder模式。

lv_layout.xml文件

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="horizontal" android:layout_width="fill_parent"    android:layout_height="fill_parent">    <ImageView        android:id="@+id/img"        android:layout_width="60dp"        android:layout_height="60dp"        android:layout_margin="5dp"        android:layout_weight="1"        />    <LinearLayout        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:orientation="vertical"        android:layout_weight="4"        >        <TextView            android:id="@+id/title"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:textSize="22sp"            />        <TextView            android:id="@+id/info"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:textSize="12sp"/>    </LinearLayout>    <Button        android:id="@+id/imgbtn"        android:layout_width="60dp"        android:layout_height="60dp"        android:layout_margin="5dp"        android:background="@drawable/selector"        android:gravity="right"        /></LinearLayout>

ViewHolder.java文件

package edu.jnu.adapterdemo;import android.widget.Button;import android.widget.ImageView;import android.widget.TextView;/** * Created by roly on 16/6/28. */final public class ViewHolder {    public ImageView imageView;    public TextView title;    public TextView info;    public Button viewBtn;}

MyAdapter.java文件

package edu.jnu.adapterdemo;import android.content.Context;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.Button;import android.widget.ImageView;import android.widget.TextView;/** * Created by roly on 16/6/28. */class MyAdapter extends BaseAdapter {    private MainActivity mainActivity;    private LayoutInflater layoutInflater;    public MyAdapter(MainActivity mainActivity, Context context) {        this.mainActivity = mainActivity;        this.layoutInflater = LayoutInflater.from(context);    }    @Override    public int getCount() {        return mainActivity.mData.size();    }    @Override    public Object getItem(int position) {        return mainActivity.mData.get(position);    }    @Override    public long getItemId(int position) {        return position;    }    @Override    public View getView(int position, View convertView, ViewGroup parent) {        ViewHolder viewHolder = null;        if (convertView == null) {            viewHolder = new ViewHolder();            convertView = layoutInflater.inflate(R.layout.lv_layout, null);            viewHolder.imageView = (ImageView) convertView.findViewById(R.id.img);            viewHolder.title = (TextView) convertView.findViewById(R.id.title);            viewHolder.info = (TextView) convertView.findViewById(R.id.info);            viewHolder.viewBtn = (Button) convertView.findViewById(R.id.imgbtn);            convertView.setTag(viewHolder);        } else {            viewHolder = (ViewHolder) convertView.getTag();        }        viewHolder.imageView.setBackgroundResource((Integer) mainActivity.mData.get(position).get("image"));        viewHolder.title.setText((String) mainActivity.mData.get(position).get("title"));        viewHolder.info.setText((String) mainActivity.mData.get(position).get("info"));        viewHolder.viewBtn.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                mainActivity.showInfo();            }        });        return convertView;    }}

MainActivity.java文件

package edu.jnu.adapterdemo;import android.app.Activity;import android.app.AlertDialog;import android.content.DialogInterface;import android.os.Bundle;import android.widget.ListView;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;public class MainActivity extends Activity {    private ListView listView;    List<Map<String,Object>> mData;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        listView = (ListView) findViewById(R.id.listView);        mData = getdata();        MyAdapter adapter = new MyAdapter(this, this);        listView.setAdapter(adapter);    }    //数据源    public List<Map<String,Object>> getdata(){        List<Map<String,Object>> list = new ArrayList<Map<String,Object>>();        Map<String,Object> map = new HashMap<String,Object>();        map.put("title","Title1");        map.put("info","Info1");        map.put("image",R.drawable.i1);        list.add(map);        map = new HashMap<String,Object>();        map.put("title","Title2");        map.put("info","Info2");        map.put("image",R.drawable.i2);        list.add(map);        map = new HashMap<String,Object>();        map.put("title","Title3");        map.put("info","Info3");        map.put("image",R.drawable.i3);        list.add(map);        return list;    }    public void showInfo(){        new AlertDialog.Builder(this)                .setTitle("Alert")                .setMessage("Introduce")                .setPositiveButton("ok",new DialogInterface.OnClickListener(){                    @Override                    public void onClick(DialogInterface dialog, int which) {                    }                })                .show();    }}

项目源码：

http://download.csdn.net/detail/ymmqwe/9562334

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