【转】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(); 
}

相关链接： 我的Android开发相关文章

转自http://blog.csdn.net/flowingflying/article/details/9243275