Android Query & managedQuery

最新推荐文章于 2021-05-26 06:40:09 发布

原创最新推荐文章于 2021-05-26 06:40:09 发布 · 129 阅读

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#Android #SQLite #Java

本文对比了使用ContentResolver.query()和Activity.managedQuery()两种方法来查询ContentProvider数据的区别。前者需手动管理Cursor生命周期，否则可能引发数据库对象未关闭的异常；后者则由Activity自动管理Cursor的生命周期，无需担心关闭及重新查询问题。

今天说一下以下两种方式query数据：

Cursor c1 = mContext.getContentResolver().query(uri, projection, selection, selectionArgs, sortOrder);

Cursor c2 = mActivity.managedQuery(uri, projection, selection, sortOrder);

使用方法一：若将Cursor c1数据放入Adapter 中,如getView() 调用加载数据，需在此Adapter对应Activity生命周期中，对Cursor进行控制，尤其要注意c1.close()的处理，否则会在反复出现如下Exception.

E/Cursor  ( 1384): Finalizing a Cursor that has not been deactivated or closed. database = /data/data/xx/databases/xx.db, table = xx, query = SELECT xx
E/Cursor  ( 1384): android.database.sqlite.DatabaseObjectNotClosedException: Application did not close the cursor or database object that was opened here
E/Cursor  ( 1384): 	at android.database.sqlite.SQLiteCursor.<init>(SQLiteCursor.java:210)
E/Cursor  ( 1384): 	at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:53)
E/Cursor  ( 1384): 	at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1345)
E/Cursor  ( 1384): 	at android.database.sqlite.SQLiteDatabase.queryWithFactory(SQLiteDatabase.java:1229)
E/Cursor  ( 1384): 	at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1184)
E/Cursor  ( 1384): 	at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1301)

使用方法二：Cursor c2 会随着Activity生命周期的变化，让Activity去控制c2的生命周期，所以不用太但心cursor是否被close,是否requery.

原文引用：

Making the query

To query a content provider, you can use either the ContentResolver.query() method or the Activity.managedQuery() method. Both methods take the same set of arguments, and both return a Cursor object. However, managedQuery() causes the activity to manage the life cycle of the Cursor. A managed Cursor handles all of the niceties, such as unloading itself when the activity pauses, and requerying itself when the activity restarts. You can ask an Activity to begin managing an unmanaged Cursor object for you by calling Activity.startManagingCursor().

以上

20110314

Consuela.