Android开发笔记之Adapter用法

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：

[b]


[/b]

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。

[b]MainActivity.java文件[/b]

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