Android的：如何使用的CursorAdapter？ [英] Android: how to use CursorAdapter?

问题描述

我有一个数据库，一个的ListView 和 CustomCursorAdapter 扩展的CursorAdapter 。菜单按钮添加一个项目到数据库中。我想的ListView 更新和显示这种变化。通常情况下它不会显示这个新的项目，直到我去到主屏幕，并重新打开应用程序。

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.

我最终获得通过调用 cursor.requery（）或 mCustomCursorAdapter.changeCursor（newCursor）工作每当我增加了一个新的项目，但是当我在的CursorAdapter 构造函数中设置autoRequery为false，它的工作一样。为什么它正确更新时autoRequery设置为false？

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?

我使用的CursorAdapter 是否正确？什么是保持更新的数据库中的表的标准方法？又是什么autoRequery办？

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

推荐答案

惯用恕我直言正确的方式来自动更新光标 s是叫<一href="http://developer.android.com/reference/android/database/Cursor.html#setNotificationUri%28android.content.ContentResolver,%20android.net.Uri%29"><$c$c>Cursor#setNotificationUri在创建时，他们被移交给任何要求之前。然后调用<一href="http://developer.android.com/reference/android/content/ContentResolver.html#notifyChange%28android.net.Uri,%20android.database.ContentObserver%29"><$c$c>ContentResolver#notifyChange当在光标什么的开放的我们的命名空间的变化。

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.

例如，假设您正在创建一个简单的邮件应用程序，你想，当新邮件到达更新，还提供了对邮件的各种意见。我有一些基本的URI定义的。

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

现在，说我希望得到一个游标这给了我所有的邮件和更新，当新邮件到达时：

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");

现在新邮件到达，所以我通知：

Now new mail arrives so I notify:

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

我也应该通知所有的光标 s表示选择标签这个新的消息见面

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);
}

和也，也许光标在查看一个特定的消息，以便通知他们还有：

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);

在 getContentResolver（）通话发生在这里被访问的数据。所以，如果它在一个服务或的ContentProvider 这是你 setNotificationUri 和有NotifyChange 。你不应该这样做，从何处访问数据，例如，一个活动。

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.

<一个href="http://android.git.kernel.org/?p=platform/packages/apps/AlarmClock.git;a=blob;f=src/com/android/alarmclock/AlarmProvider.java;h=5849a384f0b94259bc6713b9f11cf1c9749ed4ca;hb=062d863a156a3564a839ab5a718f31500298635f"><$c$c>AlarmProvider是一个简单的的ContentProvider 使用此方法来更新光标秒。

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

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