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分类: LINUX

2009-05-11 17:54:27

以前的一篇博客中,曾将介绍了如何使用content provider, 如果需要创建你自己的cotent provider,也就是定制自己特有的,你需要做的其实很简单,那就是从抽象类ContentProvider派生出你自己的类,并且实现里面所有的抽象方法,包括:

在你的content provider里面,你有随意选择存储媒介的权利,你可以用传统文件,xml,甚至是一些特定的web service, 当然你也可以选择用的最为广泛的SQLite

 

在你自己的类中,你需要定义一个public static final Uri 命名为CONTENT_URI

 

具体方法,还是通过一个例子来说明吧。

 

 

public class BooksProvider extends ContentProvider

{
   
public static final String PROVIDER_NAME =
      
"MyContentProvider"; 

   
public static final Uri CONTENT_URI =
      
Uri.parse("content://"+ PROVIDER_NAME + "/books"); 

   
public static final String _ID = "_id";
   
public static final String TITLE = "title";
   
public static final String ISBN = "isbn";
   
private static final int BOOKS = 1;
   
private static final int BOOK_ID = 2;    
   
private static final UriMatcher uriMatcher;

   
static{
      uriMatcher
= new UriMatcher(UriMatcher.NO_MATCH);
      uriMatcher
.addURI(PROVIDER_NAME, "books", BOOKS);
      uriMatcher
.addURI(PROVIDER_NAME, "books/#", BOOK_ID);
   
}

  

   
//---for database use---
   
private SQLiteDatabase booksDB;
   
private static final String DATABASE_NAME = "Books";
   
private static final String DATABASE_TABLE = "titles";
   
private static final int DATABASE_VERSION = 1;
   
private static final String DATABASE_CREATE =
         
"create table " + DATABASE_TABLE +
         
" (_id integer primary key autoincrement, "
         
+ "title text not null, isbn text not null);"; 

   @
Override
   
public boolean onCreate() {
      
Context context = getContext();
      DatabaseHelper dbHelper
= new DatabaseHelper(context);
      booksDB
= dbHelper.getWritableDatabase();
      
return (booksDB == null)? false:true;
   
}
 
   
private static class DatabaseHelper extends SQLiteOpenHelper
   
{
      DatabaseHelper
(Context context) {
         
super(context, DATABASE_NAME, null, DATABASE_VERSION);
      
}

 
      @
Override
      
public void onCreate(SQLiteDatabase db)
      
{
         db
.execSQL(DATABASE_CREATE);
      
}
 
      @
Override
      
public void onUpgrade(SQLiteDatabase db, int oldVersion,
      
int newVersion) {
         
Log.w("Content provider database",
              
"Upgrading database from version " +
              oldVersion
+ " to " + newVersion +
              
", which will destroy all old data");
         db
.execSQL("DROP TABLE IF EXISTS titles");
         onCreate
(db);
      
}
   
}
 
   @
Override
   
public String getType(Uri uri) {
      
switch (uriMatcher.match(uri)){
         
//---get all books---
         
case BOOKS:
            
return "vnd.android.cursor.dir/vnd.learn2develop.books ";
         
//---get a particular book---
         
case BOOK_ID:
            
return "vnd.android.cursor.item/vnd.learn2develop.books ";
        
default:
            
throw new IllegalArgumentException("Unsupported URI: " + uri);
      
}
   
}

   @
Override
   
public Cursor query(Uri uri, String[] projection, String selection,
     
String[] selectionArgs, String sortOrder) {   

      SQLiteQueryBuilder sqlBuilder
= new SQLiteQueryBuilder();
      sqlBuilder
.setTables(DATABASE_TABLE);   

      
if (uriMatcher.match(uri) == BOOK_ID)
         
//---if getting a particular book---
         sqlBuilder
.appendWhere(
            _ID
+ " = " + uri.getPathSegments().get(1));      

      
if (sortOrder==null || sortOrder=="")
         sortOrder
= TITLE;

        
Cursor c = sqlBuilder.query(
         booksDB
,
         projection
,
         selection
,
         selectionArgs
,
         
null,
         
null,
         sortOrder
);

     
//---register to watch a content URI for changes---
      c
.setNotificationUri(getContext().getContentResolver(), uri);
      
return c;
   
}
 
   @
Override
   
public Uri insert(Uri uri, ContentValues values) {
      
//---add a new book---
      
long rowID = booksDB.insert(
         DATABASE_TABLE
, "", values);          

      
//---if added successfully---
      
if (rowID>0)
      
{
         
Uri _uri = ContentUris.withAppendedId(CONTENT_URI, rowID);
         getContext
().getContentResolver().notifyChange(_uri,null);
        
return _uri;
      
}

      
throw new SQLException("Failed to insert row into " + uri);
   
}
 
   @
Override
   
public int delete(Uri arg0, String arg1, String[] arg2) {
      
// arg0 = uri
      
// arg1 = selection
      
// arg2 = selectionArgs

      
int count=0;
      
switch (uriMatcher.match(arg0)){
         
case BOOKS:
            
count = booksDB.delete(
               DATABASE_TABLE
,
               arg1
,
               arg2
);

            
break;

         
case BOOK_ID:
            
String id = arg0.getPathSegments().get(1);
            
count = booksDB.delete(
               DATABASE_TABLE
,
               _ID
+ " = " + id +
               
(!TextUtils.isEmpty(arg1) ? " AND (" +
               arg1
+ ')' : ""),
               arg2
);
            
break;

         
default: throw new IllegalArgumentException(
            
"Unknown URI " + arg0);

      
}

      getContext
().getContentResolver().notifyChange(arg0, null);

      
return count;

   
}

 

   @
Override

   
public int update(Uri uri, ContentValues values,

      
String selection, String[] selectionArgs)

   
{

      
int count = 0;

      
switch (uriMatcher.match(uri)){

         
case BOOKS:

            
count = booksDB.update(

               DATABASE_TABLE
,

               
values,

               selection
,

               selectionArgs
);

            
break;

         
case BOOK_ID:

            
count = booksDB.update(

               DATABASE_TABLE
,

               
values,

               _ID
+ " = " + uri.getPathSegments().get(1) +

               
(!TextUtils.isEmpty(selection) ? " AND (" +

                  selection
+ ')' : ""),

                selectionArgs
);

            
break;

         
default: throw new IllegalArgumentException(

            
"Unknown URI " + uri);

      
}

      getContext
().getContentResolver().notifyChange(uri, null);

      
return count;

   
}
}

 

 

Updated on 6/3/2009:


需要强调一点的是,如果想要建立一个自己的content provider,需要自己建立起一个UriMatcher objects 树。其中UriMatcher是一个android自带的类,用来辅助匹配当前content provider中的URI.

其中建立匹配树,需要调用UriMatcheraddURI方法:

static{
      uriMatcher
= new UriMatcher(UriMatcher.NO_MATCH);
      uriMatcher
.addURI(PROVIDER_NAME, "books", BOOKS);
      uriMatcher
.addURI(PROVIDER_NAME, "books/#", BOOK_ID);
   
}

 

当需要匹配时,需要调用uriMatcher.match方法。例如:


 

public String getType(Uri uri) {
      switch (uriMatcher.match(uri)){
         //---get all books---

         case BOOKS:
            return "vnd.android.cursor.dir/vnd.learn2develop.books ";
         //---get a particular book---
         case BOOK_ID:
            return "vnd.android.cursor.item/vnd.learn2develop.books ";
         default:
            throw new IllegalArgumentException("Unsupported URI: " + uri);
      }
   }

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给主人留下些什么吧!~~

chinaunix网友2010-10-28 14:55:12

DDDDD

chinaunix网友2009-05-12 09:22:50

很好。太感谢了。