contentprovider的学习（转发）

一、ContentProvider简介
       当应用继承ContentProvider类，并重写该类用于提供数据和存储数据的方法，就可以向其他应用共享其数据。虽然使用其他方法也可以对外共享数据，但数据访问方式会因数据存储的方式而不同，如：采用文件方式对外共享数据，需要进行文件操作读写数据；采用sharedpreferences共享数据，需要使用sharedpreferences API读写数据。而使用ContentProvider共享数据的好处是统一了数据访问方式。
二、Uri类简介
       Uri代表了要操作的数据，Uri主要包含了两部分信息：1.需要操作的ContentProvider ，2.对ContentProvider中的什么数据进行操作，一个Uri由以下几部分组成：

       1.scheme：ContentProvider（内容提供者）的scheme已经由Android所规定为：content://。
       2.主机名（或Authority）：用于唯一标识这个ContentProvider，外部调用者可以根据这个标识来找到它。
       3.路径（path）：可以用来表示我们要操作的数据，路径的构建应根据业务而定，如下：
•         要操作contact表中id为10的记录，可以构建这样的路径:/contact/10
•         要操作contact表中id为10的记录的name字段， contact/10/name
•         要操作contact表中的所有记录，可以构建这样的路径:/contact
要操作的数据不一定来自数据库，也可以是文件等他存储方式，如下:
要操作xml文件中contact节点下的name节点，可以构建这样的路径：/contact/name
如果要把一个字符串转换成Uri，可以使用Uri类中的parse()方法，如下：
Uri uri = Uri.parse("content://com.changcheng.provider.contactprovider/contact")
三、UriMatcher、ContentUrist和ContentResolver简介
       因为Uri代表了要操作的数据，所以我们很经常需要解析Uri，并从Uri中获取数据。Android系统提供了两个用于操作Uri的工具类，分别为UriMatcher 和ContentUris 。掌握它们的使用，会便于我们的开发工作。

       UriMatcher：用于匹配Uri，它的用法如下：
       1.首先把你需要匹配Uri路径全部给注册上，如下：
       //常量UriMatcher.NO_MATCH表示不匹配任何路径的返回码(-1)。
       UriMatcher  uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
       //如果match()方法匹配content://com.changcheng.sqlite.provider.contactprovider/contact路径，返回匹配码为1
       uriMatcher.addURI(“com.changcheng.sqlite.provider.contactprovider”, “contact”, 1);//添加需要匹配uri，如果匹配就会返回匹配码
       //如果match()方法匹配   content://com.changcheng.sqlite.provider.contactprovider/contact/230路径，返回匹配码为2
       uriMatcher.addURI(“com.changcheng.sqlite.provider.contactprovider”, “contact/#”, 2);//#号为通配符
      
       2.注册完需要匹配的Uri后，就可以使用uriMatcher.match(uri)方法对输入的Uri进行匹配，如果匹配就返回匹配码，匹配码是调用addURI()方法传入的第三个参数，假设匹配content://com.changcheng.sqlite.provider.contactprovider/contact路径，返回的匹配码为1。

       ContentUris：用于获取Uri路径后面的ID部分，它有两个比较实用的方法：
•         withAppendedId(uri, id)用于为路径加上ID部分
•         parseId(uri)方法用于从路径中获取ID部分

       ContentResolver：当外部应用需要对ContentProvider中的数据进行添加、删除、修改和查询操作时，可以使用ContentResolver 类来完成，要获取ContentResolver 对象，可以使用Activity提供的getContentResolver()方法。 ContentResolver使用insert、delete、update、query方法，来操作数据。
四、ContentProvider示例程序
Manifest.xml中的代码：

 

?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

<application android:icon="@drawable/icon" android:label="@string/app_name">                 <activity android:name=".TestWebviewDemo" android:label="@string/app_name">                         <intent-filter>                                 <action android:name="android.intent.action.MAIN" />                                 <category android:name="android.intent.category.LAUNCHER" />                         </intent-filter>                         <intent-filter>                                 <data android:mimeType="vnd.android.cursor.dir/vnd.ruixin.login" />                         </intent-filter>                         <intent-filter>                                 <data android:mimeType="vnd.android.cursor.item/vnd.ruixin.login" />                         </intent-filter>                                           </activity>                 <provider android:name="MyProvider" android:authorities="com.ruixin.login" />         </application>

 

需要在<application></application>中为provider进行注册！！！！
首先定义一个数据库的工具类：

?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

public class RuiXin {           public static final String DBNAME = "ruixinonlinedb";         public static final String TNAME = "ruixinonline";         public static final int VERSION = 3;                   public static String TID = "tid";         public static final String EMAIL = "email";         public static final String USERNAME = "username";         public static final String DATE = "date";         public static final String SEX = "sex";                             public static final String AUTOHORITY = "com.ruixin.login";         public static final int ITEM = 1;         public static final int ITEM_ID = 2;                   public static final String CONTENT_TYPE = "vnd.android.cursor.dir/vnd.ruixin.login";         public static final String CONTENT_ITEM_TYPE = "vnd.android.cursor.item/vnd.ruixin.login";                   public static final Uri CONTENT_URI = Uri.parse("content://" + AUTOHORITY + "/ruixinonline"); }

 

1. 然后创建一个数据库：
   
   ?

   1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

   public class DBlite extends SQLiteOpenHelper {         public DBlite(Context context) {                 super(context, RuiXin.DBNAME, null, RuiXin.VERSION);                 // TODO Auto-generated constructor stub         }         @Override         public void onCreate(SQLiteDatabase db) {                 // TODO Auto-generated method stub                         db.execSQL("create table "+RuiXin.TNAME+"(" +                                 RuiXin.TID+" integer primary key autoincrement not null,"+                                 RuiXin.EMAIL+" text not null," +                                 RuiXin.USERNAME+" text not null," +                                 RuiXin.DATE+" interger not null,"+                                 RuiXin.SEX+" text not null);");         }         @Override         public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {                 // TODO Auto-generated method stub         }         public void add(String email,String username,String date,String sex){                 SQLiteDatabase db = getWritableDatabase();                 ContentValues values = new ContentValues();                 values.put(RuiXin.EMAIL, email);                 values.put(RuiXin.USERNAME, username);                 values.put(RuiXin.DATE, date);                 values.put(RuiXin.SEX, sex);                 db.insert(RuiXin.TNAME,"",values);         } }

1. 接着创建一个Myprovider.java对数据库的接口进行包装：
   
   ?

   1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102

   public class MyProvider extends ContentProvider{           DBlite dBlite;         SQLiteDatabase db;                   private static final UriMatcher sMatcher;         static{                 sMatcher = new UriMatcher(UriMatcher.NO_MATCH);                 sMatcher.addURI(RuiXin.AUTOHORITY,RuiXin.TNAME, RuiXin.ITEM);                 sMatcher.addURI(RuiXin.AUTOHORITY, RuiXin.TNAME+"/#", RuiXin.ITEM_ID);           }         @Override         public int delete(Uri uri, String selection, String[] selectionArgs) {                 // TODO Auto-generated method stub                 db = dBlite.getWritableDatabase();                 int count = 0;                 switch (sMatcher.match(uri)) {                 case RuiXin.ITEM:                         count = db.delete(RuiXin.TNAME,selection, selectionArgs);                         break;                 case RuiXin.ITEM_ID:                         String id = uri.getPathSegments().get(1);                         count = db.delete(RuiXin.TID, RuiXin.TID+"="+id+(!TextUtils.isEmpty(RuiXin.TID="?")?"AND("+selection+')':""), selectionArgs);                     break;                 default:                         throw new IllegalArgumentException("Unknown URI"+uri);                 }                 getContext().getContentResolver().notifyChange(uri, null);                 return count;         }           @Override         public String getType(Uri uri) {                 // TODO Auto-generated method stub                 switch (sMatcher.match(uri)) {                 case RuiXin.ITEM:                         return RuiXin.CONTENT_TYPE;                 case RuiXin.ITEM_ID:                     return RuiXin.CONTENT_ITEM_TYPE;                 default:                         throw new IllegalArgumentException("Unknown URI"+uri);                 }         }           @Override         public Uri insert(Uri uri, ContentValues values) {                 // TODO Auto-generated method stub                                   db = dBlite.getWritableDatabase();                 long rowId;                 if(sMatcher.match(uri)!=RuiXin.ITEM){                         throw new IllegalArgumentException("Unknown URI"+uri);                 }                 rowId = db.insert(RuiXin.TNAME,RuiXin.TID,values);                    if(rowId>0){                            Uri noteUri=ContentUris.withAppendedId(RuiXin.CONTENT_URI, rowId);                            getContext().getContentResolver().notifyChange(noteUri, null);                            return noteUri;                    }                    throw new IllegalArgumentException("Unknown URI"+uri);         }           @Override         public boolean onCreate() {                 // TODO Auto-generated method stub                 this.dBlite = new DBlite(this.getContext()); //                db = dBlite.getWritableDatabase(); //                return (db == null)?false:true;                 return true;         }           @Override         public Cursor query(Uri uri, String[] projection, String selection,                         String[] selectionArgs, String sortOrder) {                 // TODO Auto-generated method stub                 db = dBlite.getWritableDatabase();                                Cursor c;                 Log.d("-------", String.valueOf(sMatcher.match(uri)));                 switch (sMatcher.match(uri)) {                 case RuiXin.ITEM:                         c = db.query(RuiXin.TNAME, projection, selection, selectionArgs, null, null, null);                                           break;                 case RuiXin.ITEM_ID:                         String id = uri.getPathSegments().get(1);                         c = db.query(RuiXin.TNAME, projection, RuiXin.TID+"="+id+(!TextUtils.isEmpty(selection)?"AND("+selection+')':""),selectionArgs, null, null, sortOrder);                     break;                 default:                         Log.d("!!!!!!", "Unknown URI"+uri);                         throw new IllegalArgumentException("Unknown URI"+uri);                 }                 c.setNotificationUri(getContext().getContentResolver(), uri);                 return c;         }         @Override         public int update(Uri uri, ContentValues values, String selection,                         String[] selectionArgs) {                 // TODO Auto-generated method stub                 return 0;         } }

   
   
   最后创建测试类：
   
   ?

   1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

   public class Test extends Activity {     /** Called when the activity is first created. */    private DBlite dBlite1 = new DBlite(this);;         private ContentResolver contentResolver;                     public void onCreate(Bundle savedInstanceState) {                 super.onCreate(savedInstanceState);                 setContentView(R.layout.main);                 //先对数据库进行添加数据             dBlite1.add(email,username,date,sex);             //通过contentResolver进行查找              contentResolver = TestWebviewDemo.this.getContentResolver();             Cursor cursor = contentResolver.query(                   RuiXin.CONTENT_URI, new String[] {                   RuiXin.EMAIL, RuiXin.USERNAME,                   RuiXin.DATE,RuiXin.SEX }, null, null, null);                 while (cursor.moveToNext()) {                      Toast.makeText(                     TestWebviewDemo.this,                     cursor.getString(cursor.getColumnIndex(RuiXin.EMAIL))                             + " "                             + cursor.getString(cursor.getColumnIndex(RuiXin.USERNAME))                             + " "                             + cursor.getString(cursor.getColumnIndex(RuiXin.DATE))                             + " "                             + cursor.getString(cursor.getColumnIndex(RuiXin.SEX)),                            Toast.LENGTH_SHORT).show();                      }                    startManagingCursor(cursor);  //查找后关闭游标             }         }

   
   注：上面是在一个程序中进行的测试，也可以再新建一个工程来模拟一个新的程序，然后将上面查询的代码加到新的程序当中！这样就模拟了contentprovider的数据共享功能了！
   新建个工程：TestProvider
   创建一个测试的activity
   
   ?

   1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

   public class Test extends Activity {     /** Called when the activity is first created. */         private ContentResolver contentResolver;                     public void onCreate(Bundle savedInstanceState) {                 super.onCreate(savedInstanceState);                 setContentView(R.layout.main);                             //通过contentResolver进行查找               contentResolver = TestWebviewDemo.this.getContentResolver();                                  Cursor cursor = contentResolver.query(                 RuiXin.CONTENT_URI, new String[] {                 RuiXin.EMAIL, RuiXin.USERNAME,                 RuiXin.DATE,RuiXin.SEX }, null, null, null);             while (cursor.moveToNext()) {                Toast.makeText(TestWebviewDemo.this,                        cursor.getString(cursor.getColumnIndex(RuiXin.EMAIL))                        + " "                        + cursor.getString(cursor.getColumnIndex(RuiXin.USERNAME))                        + " "                        + cursor.getString(cursor.getColumnIndex(RuiXin.DATE))                        + " "                        + cursor.getString(cursor.getColumnIndex(RuiXin.SEX)),                        Toast.LENGTH_SHORT).show();                    }                    startManagingCursor(cursor);  //查找后关闭游标             }         }

   运行此程序就能实现共享数据查询了！
   
   注：新建的程序中的manifest.xml中不需要对provider进行注册，直接运行就行，否则会报错！