0
点赞
收藏
分享

微信扫一扫

Pro Android学习笔记(八):了解Content Provider(下中)


在之前提供了小例子BookProvider,我们回过头看看如何将通过该Content Provider进行数据的读取。

(1)增加

private void addBook(String name ,String isbn,String author){ 
    /* 从ContentProvider的insert()方法的参数可以看到,通过ContentValues来进行数据的传递。ContentValues是key/values对,可以存储多个组,非常适合传递信息 */ 
    ContentValues cv = new ContentValues();     cv.put(BookTableMetaData.BOOK_NAME, name); 
     cv.put(BookTableMetaData.BOOK_ISBN, isbn); 
     cv.put(BookTableMetaData.BOOK_AUTHOR, author); 
     /* ContentResolver负责将URI reference解析到正确的provider上,并对该provider的公开的读写接口进行操作。它的方法和provider提供的方法一一对应,并增加了uri参数。*/ 
    ContentResolver cr = getContentResolver();     Uri insertUri = cr.insert(BookProviderMetaData.BookTableMetaData.CONTENT_URI, cv); //对应BookProvider的insert() 
}

(2)删除

private void delBook(String name){ 
    ContentResolver cr = getContentResolver();
     int count = cr.delete(BookProviderMetaData.BookTableMetaData.CONTENT_URI,    /* Uri          uri */ 
                     BookTableMetaData.BOOK_NAME + "=?",                    /* String         WhereClause */ 
                     new String[]{name});                                                        /* String[]        selectionArgs */ 
}

(3)修改: update和insert非常相似,也是通过ContentValues传递修改内容。

private void updateBookIsbn(String name ,String newIsbn,String newAuthor){ 
     ContentValues cv = new ContentValues(); 
     cv.put(BookTableMetaData.BOOK_NAME, name); 
     cv.put(BookTableMetaData.BOOK_ISBN, newIsbn); 
     cv.put(BookTableMetaData.BOOK_AUTHOR, newAuthor); 
     
     ContentResolver cr = getContentResolver(); 
     int count = cr.update(BookProviderMetaData.BookTableMetaData.CONTENT_URI,     /* Uri        uri */ 
                      cv,                                                                               /* ContentValues  values */ 
                      BookTableMetaData.BOOK_NAME + "=?",            /* String           WhereClause */ 
                      new String[]{name});                                                /* String[]         selectionArgs */ 
}

(4)查询

private void showBooks(){ 
     Uri uri = BookProviderMetaData.BookTableMetaData.CONTENT_URI; 
      /*方式一,通过managedQuery( )*/     @SuppressWarnings("deprecation") 
    Cursor c = managedQuery(uri, null, null, null, null);     /* 方式二:利用ContentResolver的query来获取*/
     // ContentResolver cr = getContentResolver(); 
     // Cursor c = cr.query(uri, null, null, null, null);     int iIndex = c.getColumnIndex(BookTableMetaData._ID); 
     int iName = c.getColumnIndex(BookTableMetaData.BOOK_NAME); 
     int iIsbn = c.getColumnIndex(BookTableMetaData.BOOK_ISBN); 
     int iAuthor = c.getColumnIndex(BookTableMetaData.BOOK_AUTHOR); 
/* 需要注意,通过下面showInfo显示,各列的Id并非按我们的创建table的列的顺序,所以一定要先获取列的ID。至于row的_id,是按顺序提供,为当前最大的_id+1。但除非我们能很明确清楚,一般不使用这些系统内部安排的Id */     showInfo("ColumnIndex _id=" + iIndex + ",name=" + iName + ",isdn=" + iIsbn + ", author=" + iAuthor); 
     showInfo("Totle books : " + c.getCount()); 
     for(c.moveToFirst(); !c.isAfterLast();c.moveToNext()){ 
         String id = c.getString(iIndex); 
         String name = c.getString(iName); 
         String isbn = c.getString(iIsbn); 
         String author = c.getString(iAuthor); 
         showInfo("[" +id + "]" + "\t" + name + "\t" + isbn  + "\t" + author); 
    } 
     c.close(); 
 }


举报

相关推荐

0 条评论