ContentProvider

工做中遇到了contentprovider 數據共享機制,下面來總結一下:

1、ContentProvider簡介
       當 應用繼承ContentProvider類,並重寫該類用於提供數據和存儲數據的方法,就能夠向其餘應用共享其數據。雖然使用其餘方法也能夠對外共享數據,但數據訪問方式會因數據存儲的方式而不一樣,如:採用 文件方式對外共享數據,須要進行文件操做讀寫數據;採用sharedpreferences共享數據,須要使用sharedpreferences  API讀寫數據。而使用ContentProvider共享數據的好處是統一了數據訪問方式。
2、Uri類簡介
       Uri表明了要操做的數據,Uri主要包含了兩部分信息:1.須要操做的ContentProvider ,2.對ContentProvider中的什麼數據進行操做,一個Uri由如下幾部分組成:

       1.scheme:ContentProvider(內容提供者)的scheme已經由Android所規定爲:content://。
       2.主機名(或Authority):用於惟一標識這個ContentProvider,外部調用者能夠根據這個標識來找到它。
       3.路徑(path):能夠用來表示咱們要操做的數據,路徑的構建應根據業務而定,以下:
•         要操做contact表中id爲10的記錄,能夠構建這樣的路徑:/contact/10
•         要操做contact表中id爲10的記錄的name字段, contact/10/name
•         要操做contact表中的全部記錄,能夠構建這樣的路徑:/contact
要操做的數據不必定來自 數據庫,也能夠是文件等他存儲方式,以下:
要操做xml文件中contact節點下的name節點,能夠構建這樣的路徑:/contact/name
若是要把一個字符串轉換成Uri,可使用Uri類中的parse()方法,以下:
Uri uri = Uri.parse("content://com.changcheng.provider.contactprovider/contact")
3、UriMatcher、ContentUrist和ContentResolver簡介
       由於Uri表明了要操做的數據,因此咱們很常常須要解析Uri,並從Uri中 獲取數據。Android 系統提供了兩個用於操做Uri的工具類,分別爲UriMatcher 和ContentUris 。掌握它們的使用,會便於咱們的 開發工做。

       UriMatcher:用於匹配Uri,它的用法以下:
       1.首先把你須要匹配Uri路徑所有給註冊上,以下:
       //常量UriMatcher.NO_MATCH表示不匹配任何路徑的返回碼(-1)。
       UriMatcher  uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
       //若是match()方法匹配content://com.changcheng.sqlite.provider.contactprovider/contact路徑,返回匹配碼爲1
       uriMatcher.addURI(「com.changcheng.sqlite.provider.contactprovider」, 「contact」, 1);//添加須要匹配uri,若是匹配就會返回匹配碼
       //若是match()方法匹配   content://com.changcheng.sqlite.provider.contactprovider/contact/230路徑,返回匹配碼爲2
       uriMatcher.addURI(「com.changcheng.sqlite.provider.contactprovider」, 「contact/#」, 2);//#號爲通配符
      
       2.註冊完須要匹配的Uri後,就可使用uriMatcher.match(uri)方法對輸入的Uri進行匹配,若是匹配就返回匹配碼,匹配碼是調用addURI()方法傳入的第三個參數,假設匹配content://com.changcheng.sqlite.provider.contactprovider/contact路徑,返回的匹配碼爲1。

       ContentUris:用於獲取Uri路徑後面的ID部分,它有兩個比較實用的方法:
•         withAppendedId(uri, id)用於爲路徑加上ID部分
•         parseId(uri)方法用於從路徑中獲取ID部分

       ContentResolver:當外部應用須要對ContentProvider中的數據進行添加、刪除、修改和查詢操做時,可使用ContentResolver 類來完成,要獲取ContentResolver 對象,可使用Activity提供的getContentResolver()方法。 ContentResolver使用insert、delete、update、query方法,來操做數據。
4、ContentProvider示例 程序
Manifest.xml中的 代碼

 

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<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>
 

須要在<application></application>中爲provider進行註冊!!!!
首先定義一個數據庫的工具類:html

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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. 而後建立一個數據庫:
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    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. 接着建立一個Myprovider.java對數據庫的接口進行包裝:
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    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 ;
             }
    }


    最後建立測試類:
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    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);
                     //先對數據庫進行添加數據
                 dBlite1.add(email,username,date,sex);
                 //經過contentResolver進行查找
                  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);   //查找後關閉遊標
                 }
             }

    注:上面是在一個程序中進行的測試,也能夠再新建一個工程來模擬一個新的程序,而後將上面查詢的代碼加到新的程序當中!這樣就模擬了contentprovider的數據共享功能了!
    新建個工程:TestProvider
    建立一個測試的activity
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    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);
                    
                 //經過contentResolver進行查找
                   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);   //查找後關閉遊標
                 }
             }
    運行此程序就能實現共享數據查詢了!注:新建的程序中的manifest.xml中不須要對provider進行註冊,直接運行就行,不然會報錯!
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