Android中的adapter

Adapter介绍

Android是完全遵循MVC模式设计的框架,Activity是Controller,layout是View
因为layout五花八门,很多数据都不能直接绑定上去,所以Android引入了Adapter这个机制作为复杂数据的展示的转换载体,所以各种Adapter只不过是转换的方式和能力不一样而已。
几种常用的Adapter:

其中BaseAdapter的直接子类：
ArrayAdapter<T>, CursorAdapter, SimpleAdapter

BaseAdapter的间接子类：
ResourceCursorAdapter, SimpleCursorAdapter

Adapter是将数据绑定到UI界面上的桥接类。Adapter负责创建显示每个项目的子View和提供对下层数据的访问。

在多数情况下，你不需要白手创建自己的Adapter。Android提供了一系列Adapter来将数据绑定到UI Widget上。

因为Android负责提供数据和选择用于显示每个项目的View，所以Adapter能快速地修改要绑定的控件的外观和功能。下面的列表显示了两个最有用和最通用的本地Adapter：

❑ ArrayAdapter
ArrayAdapter是一个绑定View到一组对象的通用类。默认情况下，ArrayAdapter绑定每个对象的toString值到在layout中预先定义的TextView控件上。可变通的，构造函数允许你使用更加复杂的layout或者通过重写getView方法来扩展类从而使用TextView的替代物（如ImageView或嵌套的layout）。

❑ SimpleCursorAdapter
SimpleCursorAdapter绑定View到Content Provider查询返回的游标上。指定一个XML layout定义，然后将数据集中的每一列的值绑定到layout中的一个View上。

下面演示一下SimpleAdapter的用法：

package com.wt.app;import java.util.ArrayList;import java.util.HashMap;import android.app.Activity;import android.os.Bundle;import android.view.ContextMenu;import android.view.MenuItem;import android.view.View;import android.view.ContextMenu.ContextMenuInfo;import android.view.View.OnCreateContextMenuListener;import android.widget.AdapterView;import android.widget.ListView;import android.widget.SimpleAdapter;import android.widget.AdapterView.OnItemClickListener;public class App extends Activity {@Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        //绑定Layout里面的ListView        ListView list = (ListView) findViewById(R.id.ListView01);                //生成动态数组，加入数据        ArrayList<HashMap<String, Object>> listItem = new ArrayList<HashMap<String, Object>>();        int[] images=new int[]{android.R.drawable.ic_menu_add,android.R.drawable.ic_menu_delete,android.R.drawable.ic_menu_edit,android.R.drawable.ic_menu_view};        for(int i=0;i<4;i++)        {        HashMap<String, Object> map = new HashMap<String, Object>();        map.put("itemImage", images[i]);//图像资源的ID        map.put("itemTitle", "Title "+i);        map.put("itemText", "this is Text "+i);        listItem.add(map);        }        //生成适配器的Item和动态数组对应的元素        SimpleAdapter listItemAdapter = new SimpleAdapter(this,listItem,//数据源             R.layout.row,//ListItem的XML实现            //动态数组与ImageItem对应的子项                    new String[] {"itemImage","itemTitle", "itemText"},             //ImageItem的XML文件里面的一个ImageView,两个TextView ID            new int[] {R.id.itemImage,R.id.itemTitle,R.id.itemText}        );               //添加并且显示        list.setAdapter(listItemAdapter);        //添加点击        list.setOnItemClickListener(new OnItemClickListener() {public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,long arg3) {setTitle("点击第"+arg2+"个项目");}});              //添加长按点击        list.setOnCreateContextMenuListener(new OnCreateContextMenuListener() {public void onCreateContextMenu(ContextMenu menu, View v,ContextMenuInfo menuInfo) {menu.setHeaderTitle("长按菜单-ContextMenu");   menu.add(0, 0, 0, "弹出长按菜单0");menu.add(0, 1, 0, "弹出长按菜单1");   }});     }//长按菜单响应函数@Overridepublic boolean onContextItemSelected(MenuItem item) {setTitle("点击了长按菜单里面的第"+item.getItemId()+"个项目"); return super.onContextItemSelected(item);}}

整体布局文件，一个简单的ListView：

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    ><ListView android:layout_width="wrap_content"             android:layout_height="wrap_content"             android:id="@+id/ListView01"      />  </LinearLayout>

ListView中每行（row）怎么显示的布局文件：

<?xml version="1.0" encoding="utf-8"?><RelativeLayout android:id="@+id/RelativeLayout01" android:layout_width="fill_parent" xmlns:android="http://schemas.android.com/apk/res/android" android:layout_height="wrap_content" android:paddingTop="4dip" android:paddingBottom="4dip" android:paddingLeft="12dip"android:paddingRight="12dip"><ImageView android:paddingTop="12dip"android:layout_alignParentRight="true"android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/itemImage"/> <TextView     android:layout_height="wrap_content"     android:textSize="20dip"     android:layout_width="fill_parent"     android:id="@+id/itemTitle"    /><TextView android:layout_height="wrap_content" android:layout_width="fill_parent" android:layout_below="@+id/itemTitle" android:id="@+id/itemText"/></RelativeLayout>

下面演示了BaseExpandableListAdapter的用法：

/* * Copyright (C) 2007 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * *      http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package com.example.android.apis.view;import android.app.ExpandableListActivity;import android.os.Bundle;import android.view.ContextMenu;import android.view.Gravity;import android.view.MenuItem;import android.view.View;import android.view.ViewGroup;import android.view.ContextMenu.ContextMenuInfo;import android.widget.AbsListView;import android.widget.BaseExpandableListAdapter;import android.widget.ExpandableListAdapter;import android.widget.ExpandableListView;import android.widget.TextView;import android.widget.Toast;import android.widget.ExpandableListView.ExpandableListContextMenuInfo;import com.example.android.apis.R;/** * Demonstrates expandable lists using a custom {@link ExpandableListAdapter} * from {@link BaseExpandableListAdapter}. */public class ExpandableList1 extends ExpandableListActivity {    ExpandableListAdapter mAdapter;    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        // Set up our adapter        mAdapter = new MyExpandableListAdapter();        setListAdapter(mAdapter);        registerForContextMenu(getExpandableListView());    }    @Override    public void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo) {        menu.setHeaderTitle("Sample menu");        menu.add(0, 0, 0, R.string.expandable_list_sample_action);    }        @Override    public boolean onContextItemSelected(MenuItem item) {        ExpandableListContextMenuInfo info = (ExpandableListContextMenuInfo) item.getMenuInfo();        String title = ((TextView) info.targetView).getText().toString();                int type = ExpandableListView.getPackedPositionType(info.packedPosition);        if (type == ExpandableListView.PACKED_POSITION_TYPE_CHILD) {            int groupPos = ExpandableListView.getPackedPositionGroup(info.packedPosition);             int childPos = ExpandableListView.getPackedPositionChild(info.packedPosition);             Toast.makeText(this, title + ": Child " + childPos + " clicked in group " + groupPos,                    Toast.LENGTH_SHORT).show();            return true;        } else if (type == ExpandableListView.PACKED_POSITION_TYPE_GROUP) {            int groupPos = ExpandableListView.getPackedPositionGroup(info.packedPosition);             Toast.makeText(this, title + ": Group " + groupPos + " clicked", Toast.LENGTH_SHORT).show();            return true;        }                return false;    }    /**     * A simple adapter which maintains an ArrayList of photo resource Ids.      * Each photo is displayed as an image. This adapter supports clearing the     * list of photos and adding a new photo.     *     */    public class MyExpandableListAdapter extends BaseExpandableListAdapter {        // Sample data set.  children[i] contains the children (String[]) for groups[i].        private String[] groups = { "People Names", "Dog Names", "Cat Names", "Fish Names" };        private String[][] children = {                { "Arnold", "Barry", "Chuck", "David" },                { "Ace", "Bandit", "Cha-Cha", "Deuce" },                { "Fluffy", "Snuggles" },                { "Goldy", "Bubbles" }        };                public Object getChild(int groupPosition, int childPosition) {            return children[groupPosition][childPosition];        }        public long getChildId(int groupPosition, int childPosition) {            return childPosition;        }        public int getChildrenCount(int groupPosition) {            return children[groupPosition].length;        }        public TextView getGenericView() {            // Layout parameters for the ExpandableListView            AbsListView.LayoutParams lp = new AbsListView.LayoutParams(                    ViewGroup.LayoutParams.MATCH_PARENT, 64);            TextView textView = new TextView(ExpandableList1.this);            textView.setLayoutParams(lp);            // Center the text vertically            textView.setGravity(Gravity.CENTER_VERTICAL | Gravity.LEFT);            // Set the text starting position            textView.setPadding(36, 0, 0, 0);            return textView;        }                public View getChildView(int groupPosition, int childPosition, boolean isLastChild,                View convertView, ViewGroup parent) {            TextView textView = getGenericView();            textView.setText(getChild(groupPosition, childPosition).toString());            return textView;        }        public Object getGroup(int groupPosition) {            return groups[groupPosition];        }        public int getGroupCount() {            return groups.length;        }        public long getGroupId(int groupPosition) {            return groupPosition;        }        public View getGroupView(int groupPosition, boolean isExpanded, View convertView,                ViewGroup parent) {            TextView textView = getGenericView();            textView.setText(getGroup(groupPosition).toString());            return textView;        }        public boolean isChildSelectable(int groupPosition, int childPosition) {            return true;        }        public boolean hasStableIds() {            return true;        }    }}

SimpleCursorTreeAdapter用法：

/* * Copyright (C) 2007 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * *      http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package com.example.android.apis.view;import android.app.ExpandableListActivity;import android.content.ContentUris;import android.content.Context;import android.database.Cursor;import android.net.Uri;import android.os.Bundle;import android.provider.Contacts.People;import android.widget.ExpandableListAdapter;import android.widget.SimpleCursorTreeAdapter;/** * Demonstrates expandable lists backed by Cursors */public class ExpandableList2 extends ExpandableListActivity {    private int mGroupIdColumnIndex;         private String mPhoneNumberProjection[] = new String[] {            People.Phones._ID, People.Phones.NUMBER    };        private ExpandableListAdapter mAdapter;        @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        // Query for people        Cursor groupCursor = managedQuery(People.CONTENT_URI,                new String[] {People._ID, People.NAME}, null, null, null);        // Cache the ID column index        mGroupIdColumnIndex = groupCursor.getColumnIndexOrThrow(People._ID);        // Set up our adapter        mAdapter = new MyExpandableListAdapter(groupCursor,                this,                android.R.layout.simple_expandable_list_item_1,                android.R.layout.simple_expandable_list_item_1,                new String[] {People.NAME}, // Name for group layouts                new int[] {android.R.id.text1},                new String[] {People.NUMBER}, // Number for child layouts                new int[] {android.R.id.text1});        setListAdapter(mAdapter);    }    public class MyExpandableListAdapter extends SimpleCursorTreeAdapter {        public MyExpandableListAdapter(Cursor cursor, Context context, int groupLayout,                int childLayout, String[] groupFrom, int[] groupTo, String[] childrenFrom,                int[] childrenTo) {            super(context, cursor, groupLayout, groupFrom, groupTo, childLayout, childrenFrom,                    childrenTo);        }        @Override        protected Cursor getChildrenCursor(Cursor groupCursor) {            // Given the group, we return a cursor for all the children within that group             // Return a cursor that points to this contact's phone numbers            Uri.Builder builder = People.CONTENT_URI.buildUpon();            ContentUris.appendId(builder, groupCursor.getLong(mGroupIdColumnIndex));            builder.appendEncodedPath(People.Phones.CONTENT_DIRECTORY);            Uri phoneNumbersUri = builder.build();            // The returned Cursor MUST be managed by us, so we use Activity's helper            // functionality to manage it for us.            return managedQuery(phoneNumbersUri, mPhoneNumberProjection, null, null, null);        }    }}

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