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androidandroid-cursoradapter

Android: how to use CursorAdapter?

I have a database, a ListView, and a CustomCursorAdapter that extends CursorAdapter. A menu button adds an item to the database. I want the ListView to update and show this change. Normally it doesn't show this new item until i go to the homescreen and reopen the application.

I did eventually get it to work by calling cursor.requery() or mCustomCursorAdapter.changeCursor(newCursor) whenever I added a new item, but when I set autoRequery to false in the CursorAdapter constructor, it worked just the same. Why does it update correctly when autoRequery is set to false?

Am I using CursorAdapter correctly? What is the standard way of keeping the list updated with the database? And what does autoRequery do?

Solution

  • The idiomatic and imho correct way to automatically update Cursors is to call Cursor#setNotificationUri when they are created and before they are handed off to whatever requested them. Then call ContentResolver#notifyChange when anything in that Cursor's Uri's namespace changes.

    For example, suppose you were creating a simple mail application and you wanted to update when new mail arrived but also provide various views on the mail. I'd have some basic Uri's defined.

    content://org.example/all_mail
content://org.example/labels
content://org.example/messages

    Now, say I wanted to get a cursor that gave me all mail and be updated when new mail arrives:

    Cursor c;
//code to get data
c.setNotificationUri(getContentResolver(), Uri.parse("content://org.example/all_mail");

    Now new mail arrives so I notify:

    //Do stuff to store in database
getContentResolver().notifyChange(Uri.parse("content://org.example/all_mail", null);

    I should also notify all the Cursors that selected for labels this new message met

    for(String label : message.getLabels() {
  getContentResolver().notifyChange(Uri.parse("content://org.example/lables/" + label, null);
}

    And also, maybe a cursor is viewing that one specific message so notify them as well:

    getContentResolver().notifyChange(Uri.parse("content://org.example/messages/" + message.getMessageId(), null);

    The getContentResolver() calls happen where the data is accessed. So if it's in a Service or ContentProvider that is where you setNotificationUri and notifyChange. You should not be doing that from where the data is accessed, e.g., an Activity.

    AlarmProvider is a simple ContentProvider that uses this method to update Cursors.