android开发

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, 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 
    @Override 
    public 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); 
        } 
    } 
}
泡在网上的日子
每天进步一点点
0

粉丝

0

关注

0

获赞

0

访问

推荐文章