Android-ContentProvider数据库操作

在实际的开发过程中，Android提供了5种方式存储数据：   

1.文件存储数据    
2.使用 Sharedpreferences 存储数据    
3.SQLite数据库存储数据    
4.使用ContentProvider存储数据    
5.网络存储数据

首先我们先简单了解下文件、SharedPreferred如何进行数据存储

1.文件存储操作

    文件存储一般存储在sdcard或者ROM，当文件存储在ROM上时，如果是存储在除自己私有空间外(data/data/包名/)，在其他地方是需要system系统权限的（http://my.oschina.net/zhoulc/blog/119282）。

    文件IO流创建比较简单，就不详述了，在进行文件存储的时候注意两个路径方法就行。
    存储到ROM：
        Context mContext = XXXActivity.this;
        mContext.getFilesDir().getAbsolutePath();
        获取路径：/data/data/包名/files
    存储到sdCard :
        首先判断sdcard是否可用
         Environment.getExternalStorageState()是否等于Environment.MEDIA_MOUNTED
         Environment.getExternalStorageDirectory().getAbsolutePath()
         对sdcard目录操作需要添加权限： 
            
         < uses-permission   android:name          ="android.permission.WRITE_EXTERNAL_STORAGE" >
         获取路径：/sdcard
    拓展下 ：支持u盘的移动设备，u盘一般都是挂载mnt/sda/sdal外设上面
    顺带说下以前一直纠结的一个问题:
        getApplicationContext() 生命周期是整个应用，应用摧毁它才摧毁
        Activity.this的context属于activity ，activity 摧毁他就摧毁

2.通过Sharedpreferences进行数据存储

"line-height:19px;" > private final static String PERFS_NAME = "com.zlc.test" ;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super .onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //存放
        //第一个参数是存储时的名称，第二个参数则是文件的打开方式(Context.
MODE_PRIVATE)
        SharedPreferences userInfo = getSharedPreferences(PERFS_NAME, 0 );
        SharedPreferences.Editor editor = userInfo.edit();
        editor.putString( "userName" , "zhoulc" );
        editor.putString( "passWord" , "ds" );
        editor.commit();
        //读取
        System.out.println( "##########################################" );
        SharedPreferences readInfo = getSharedPreferences(PERFS_NAME, 0 );
        String name = readInfo.getString( "userName" , "no_name" );
        String psword = readInfo.getString( "passWord" , "000000" );
        System.out.println( "name = " +name+ " password = " +psword);
    }

使用过程中注意三个问题： 

    1）getSharedPreferences有两个参数，第一个参数是存储时的名称， 第二个参数则是文件的打开方式(一般使用0或者Context.MODE_PRIVATE) 
    2）默认的模式为0或MODE_PRIVATE，如果访问其他应用中的Preference，前提条件是：该 preference创建时指定了Context.MODE_WORLD_READABLE或者Context.MODE_WORLD_WRITEABLE权限。 
    3）千万不要偷懒写成 
        userInfo.edit().putString("userName", "zhoulc"); 
        userInfo.edit().putString("passWord", "ds"); 
        userInfo.edit().commit(); 
        edit()方法每次都要产生一个新的SharedPreferences.Edit类的对象，所以commit 
之后数据没有存储成功。 

3.其他几个就不详细介绍了，说下今天的重点ContentProvider

    创建一个可对数据库进行操作的ContentProvider我们先要了解涉及到的知识点：
    （1）Parcelable（实体类数据一般会用在进程之间通信）
           http://my.oschina.net/zhoulc/blog/172163
    （2）BaseColumns，这个类只是提供了两个字段，一个是"_id"一个是"_count"，便于调用数据库时导致拼写错误，你也可以扩展它，或者自定义这么个，然后直接调用它的常量名，防止写sql语句时把列名拼错。

"line-height:19px;" > package android.provider;

public interface BaseColumns
{
    /**
     * The unique ID for a row.
     * Type: INTEGER (long)
     */
    public static final String _ID = "_id" ;

    /**
     * The count of rows in a directory.
     * Type: INTEGER
     */
    public static final String _COUNT = "_count" ;
}

    （3）SQLiteOpenHelper，包装了数据库的创建、打开、更新的抽象类，通过实现和使用SQLiteOpenHandle可以隐去数据库打开的之前判断数据库是否需要创建或更新的逻辑。 
            主要实现三个方法 
            创建数据库：public DatabaseHelper(Context context) 
              创建表：public void onCreate(SQLiteDatabase db) 
            更新表：public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
      （4）UriMatcher用来匹配URI。 
            主要实现两个接口： 
              添加需要匹配的URI：MATCHER.addURI(String authority, String path, int code) 进行匹配返回定义的value；MATCHER.match(Uri uri) 
            例： 
                MATCHER.addURI(Information.AUTHORITY, "informations", INFORMATIONS); 
                MATCHER.addURI(Information.AUTHORITY, "informations/#", INFORMATION); 
                # 号为通配符 
                * 号为任意字符 
    （5）ContentUris一个工具类，主要是用来处理使用 "content" 约束的Uri对象，经常用到条件查询某个_ID的数据。 
            主要实现两个接口： 
            static long parseId(Uri contentUri)  将uri中的id解析出来，此方法返回的是一个long型的id。 
            static Uri withAppendedId(Uri contentUri, long id)在指定的uri后面添加一条id 
为指定参数的记录。  
    （6）SQLiteDatabase，这个类是核心类，用于管理和操作SQLite数据库，几乎所有的数据库操作，最终都将由这个类完成。 
    （7）ContentProvider，提供数据库增删改查的接口。 
            主要实现接口： 
            public int delete(Uri uri, String selection, String[] selectionArgs) 
            public String getType(Uri uri) 
            public Uri insert(Uri uri, ContentValues values) 
            public boolean onCreate() 
            public Cursor query(Uri uri, String[] projection, String selection,String[] selectionArgs, String sortOrder) 
            public int update(Uri uri, ContentValues values, String selection, 
String[] selectionArgs) 
    （8）ContentResolver接口和ContentProvider类似，两个区别一个是用户是通过ContentResolver调用ContentProvider提供的接口。 
    以上类都只是简单介绍，有兴趣的朋友可以去研究下源码和实现过程。这里主要讲使用过程和一些注意细节。 


4.ContentProvider 在使用过程中需要注意两点： 

    （1）在AndroidManifest.xml里面需要注册这个ContentProvider      
             
    （2）当提供给其他进程调用（假如是其他应用），如果当前提供ContentProvider的应用在退出的时候把自己给kill掉了（这个时候ContentProvider也无法使用），则我们需要在AndroidManifest.xml里面再添加一条属性 
            android:process="com.zlc.provider.MyProvider" 
            为该组件指定一个不同的默认进程 

5.下面贴一下具体实现代码：

      （1）ContentProvider提供者TestContentProvider.apk 
            实体类：Information.java 

package com.zlc.provider;

import android.net.Uri;
import android.os.Parcel;
import android.os.Parcelable;
import android.provider.BaseColumns;

public class Information implements Parcelable,BaseColumns{
    public final static String AUTHORITY = "com.zlc.provider.MyProvider" ;
    public final static Uri CONTENT_URI = Uri.parse( "content://" +AUTHORITY+ "/informations" );
    //表字段
    public final static String INFO_ID = "info_id" ;
    public final static String INFO_NAME = "info_name" ;
    public final static String INFO_AGE = "info_age" ;

    private String info_id,info_name,info_age;

    public Information(Parcel source){
        info_id = source.readString();
        info_name = source.readString();
        info_age = source.readString();
    }
    public String getInfo_id() {
        return info_id;
    }

    public void setInfo_id(String info_id) {
        this .info_id = info_id;
    }

    public String getInfo_name() {
        return info_name;
    }

    public void setInfo_name(String info_name) {
        this .info_name = info_name;
    }

    public String getInfo_age() {
        return info_age;
    }

    public void setInfo_age(String info_age) {
        this .info_age = info_age;
    }

    @Override
    public int describeContents() {
        // TODO Auto-generated method stub
        return 0 ;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        // TODO Auto-generated method stub
        dest.writeString(info_id);
        dest.writeString(info_name);
        dest.writeString(info_age);
    }
    public final static Parcelable.Creator CREATOR = new Parcelable.Creator() {

        @Override
        public Information createFromParcel(Parcel source) {
            // TODO Auto-generated method stub
            return new Information(source);
        }

        @Override
        public Information[] newArray( int size) {
            // TODO Auto-generated method stub
            return new Information[size];
        }
    };
}

            MyProvider.java 

package com.zlc.provider;

import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.Context;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.net.Uri;
import android.provider.BaseColumns;
import android.util.Log;

public class MyProvider extends ContentProvider {
    private SQLiteDatabase sqDb;
    private DatabaseHelper helper;
    // 数据库名
    private final static String DATABASE_NAME = "zhoulc.db" ;
    // 版本
    private static final int DATABASE_VERSION = 1 ;
    // 表名
    private static final String TABLE_NAME = "Information" ;
    // 创建表的sql语句
    private final static String CREATE_TABLE = "Create table " + TABLE_NAME
            + "( " +Information._ID+ " integer primary key autoincrement," + Information.INFO_ID
            + " TEXT," + Information.INFO_NAME + " TEXT," + Information.INFO_AGE
            + " TEXT);" ;

    // Declaration Datababsehelper
    private static class DatabaseHelper extends SQLiteOpenHelper {

        public DatabaseHelper(Context context) {
            super (context, DATABASE_NAME, null , DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            // TODO Auto-generated method stub
            db.execSQL(CREATE_TABLE);
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            // TODO Auto-generated method stub
            db.execSQL( "DROP TABLE IF EXISTS" + TABLE_NAME);
            onCreate(db);
        }

    }

    // UriMatcher add URI
    private static final UriMatcher MATCHER = new UriMatcher(
            UriMatcher.NO_MATCH);
    private final static int INFORMATIONS = 1 ;
    private final static int INFORMATION = 2 ;
    static {
        MATCHER.addURI(Information.AUTHORITY, "informations" , INFORMATIONS);
        MATCHER.addURI(Information.AUTHORITY, "informations/#" , INFORMATION);
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        // TODO Auto-generated method stub
        sqDb = helper.getWritableDatabase();
        int count = 0 ;
        switch (MATCHER.match(uri)) {
        case INFORMATIONS:
            count = sqDb.delete(TABLE_NAME, selection, selectionArgs);
            break ;
        default :
            throw new IllegalArgumentException( "Unkwon Uri:" + uri.toString());
        }
        return count;
    }

    @Override
    public String getType(Uri uri) {
        // TODO Auto-generated method stub
        switch (MATCHER.match(uri)) {
        case INFORMATIONS:
            return "vnd.android.cursor.dir/Information" ;
        case INFORMATION:
            return "vnd.android.cursor.item/Information" ;
        default :
            throw new IllegalArgumentException( "Unkwon Uri:" + uri.toString());
        }
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        // TODO Auto-generated method stub
        sqDb = helper.getWritableDatabase();
        Uri insertUri = null ;
        long rowid = 0 ;
        switch (MATCHER.match(uri)) {
        case INFORMATIONS:
            rowid = sqDb.insert(TABLE_NAME, Information.INFO_ID, values);
            insertUri = ContentUris.withAppendedId(uri, rowid);
            Log.i( "zhoulc" , "insert record...values:" + values.toString());
            break ;
        default :
            throw new IllegalArgumentException( "Unkwon Uri:" + uri.toString());
        }
        return insertUri;
    }

    @Override
    public boolean onCreate() {
        // TODO Auto-generated method stub
        helper = new DatabaseHelper(getContext());
        return helper == null ? false : true ;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
            String[] selectionArgs, String sortOrder) {
        // TODO Auto-generated method stub
        sqDb = helper.getWritableDatabase();
        switch (MATCHER.match(uri)) {
        case INFORMATIONS:
            Cursor cursor = sqDb.query(TABLE_NAME, projection, selection,
                    selectionArgs, null , null , sortOrder);
            return cursor;
        case INFORMATION: //条件查询，
            long id = ContentUris.parseId(uri);
            String where = Information._ID + "=" + id;
             if (selection != null && ! "" .equals(selection))
             {
                 where = where + " and " + selection;
             }
             return sqDb.query(TABLE_NAME, projection, where, selectionArgs, null ,
                 null , sortOrder);
        default :
            throw new IllegalArgumentException( "unknow uri" + uri.toString());
        }
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection,
            String[] selectionArgs) {
        // TODO Auto-generated method stub
        sqDb = helper.getWritableDatabase();
        int count = 0 ;
        switch (MATCHER.match(uri)) {
        case INFORMATIONS:
            count = sqDb.update(TABLE_NAME, values, selection, selectionArgs);
            return count;
        default :
            throw new IllegalArgumentException( "unknow uri" + uri.toString());
        }

    }

}

            在同一个应用本身里面（进程）测试插入数据:MainActivity.java

package com.zlc.provider;

import android.app.Activity;
import android.content.ContentValues;
import android.content.Context;
import android.content.pm.ApplicationInfo;
import android.content.pm.PackageManager;
import android.content.pm.PackageManager.NameNotFoundException;
import android.net.Uri;
import android.os.Bundle;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super .onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Context mContext = MainActivity. this ;
        Uri myUri = Information.CONTENT_URI;
       &nbs