ContentProvider官方教程(7)3种访问形式：批处理、异步访问、intent间接访问(临时URI权限)

Alternative Forms of Provider Access

　　Three alternative forms of provider access are important in application development:

• Batch access: You can create a batch of access calls with methods in the ContentProviderOperation class, and then apply them with ContentResolver.applyBatch().

  批处理式访问

• Asynchronous queries: You should do queries in a separate thread. One way to do this is to use a CursorLoader object. The examples in the Loaders guide demonstrate how to do this.

  异步访问，通过CursorLoader在其它线程中查询。本文不介绍这种方式，在Loaders中有示例。

• Data access via intents: Although you can't send an intent directly to a provider, you can send an intent to the provider's application, which is usually the best-equipped to modify the provider's data.

  通过intent间接访问。

　　Batch access and modification via intents are described in the following sections.

Batch access 批处理

　　Batch access to a provider is useful for inserting a large number of rows, or for inserting rows in multiple tables in the same method call, or in general for performing a set of operations across process boundaries as a transaction (an atomic operation).

　　To access a provider in "batch mode", you create an array of ContentProviderOperation objects and then dispatch them to a content provider with ContentResolver.applyBatch(). You pass the content provider's authority to this method, rather than a particular content URI. This allows each ContentProviderOperation object in the array to work against a different table. A call to ContentResolver.applyBatch() returns an array of results.

　　批处理方式使用的类是ContentProviderOperation。ContactAdder.java中有示例代码。

　　The description of the ContactsContract.RawContacts contract class includes a code snippet that demonstrates batch insertion. The Contact Manager sample application contains an example of batch access in its ContactAdder.java source file.

Data access via intents 通过intent方式间接访问

　　Intents can provide indirect access to a content provider. You allow the user to access data in a provider even if your application doesn't have access permissions, either by getting a result intent back from an application that has permissions, or by activating an application that has permissions and letting the user do work in it.

　　一个有权限的应用访问provider,然后用intent与这个应用交互来实现间接访问provider.

Getting access with temporary permissions 申请临时URI权限 然后访问

　　You can access data in a content provider, even if you don't have the proper access permissions, by sending an intent to an application that does have the permissions and receiving back a result intent containing "URI" permissions. These are permissions for a specific content URI that last until the activity that receives them is finished. The application that has permanent permissions grants temporary permissions by setting a flag in the result intent:

　　有权限的应用可以在intent中设置下面两个标记然后返回，包含了临时URI权限。

• Read permission: FLAG_GRANT_READ_URI_PERMISSION
• Write permission: FLAG_GRANT_WRITE_URI_PERMISSION

　　Note: These flags don't give general read or write access to the provider whose authority is contained in the content URI. The access is only for the URI itself.

　　注意：这个临时权限只是当前这个URI的，并不是整个数据库的。

　　A provider defines URI permissions for content URIs in its manifest, using the android:grantUriPermission attribute of the <provider> element, as well as the <grant-uri-permission> child element of the <provider> element. The URI permissions mechanism is explained in more detail in the Security and Permissions guide, in the section "URI Permissions".

　　在 <provider android:grantUriPermission >...和它的子元素 <grant-uri-permission> 可以声明一个URI权限。

　　For example, you can retrieve data for a contact in the Contacts Provider, even if you don't have the READ_CONTACTS permission. You might want to do this in an application that sends e-greetings to a contact on his or her birthday. Instead of requesting READ_CONTACTS, which gives you access to all of the user's contacts and all of their information, you prefer to let the user control which contacts are used by your application. To do this, you use the following process:

　　下面是一个没有Contact Provider访问权限的应用通过申请临时URI权限访问Contact Provider的步骤：

1. Your application sends an intent containing the action ACTION_PICK and the "contacts" MIME type CONTENT_ITEM_TYPE, using the method startActivityForResult().

   在intent中设置ACTION_PICK和 CONTENT_ITEM_TYPE ，然后调用startActivityForResult()启动People app's "selection" activity.

2. Because this intent matches the intent filter for the People app's "selection" activity, the activity will come to the foreground.

   People app's "selection" activity到前台。

3. In the selection activity, the user selects a contact to update. When this happens, the selection activity calls setResult(resultcode, intent) to set up a intent to give back to your application. The intent contains the content URI of the contact the user selected, and the "extras" flags FLAG_GRANT_READ_URI_PERMISSION. These flags grant URI permission to your app to read data for the contact pointed to by the content URI. The selection activity then calls finish() to return control to your application.

   "selection" activity会在返回 Intent中添加临时URI权限 FLAG_GRANT_READ_URI_PERMISSION,然后它自己调用finish()

4. Your activity returns to the foreground, and the system calls your activity's onActivityResult() method. This method receives the result intent created by the selection activity in the People app.

   你的应用收到由"selection" activity返回的带有临朝权限的intent

5. With the content URI from the result intent, you can read the contact's data from the Contacts Provider, even though you didn't request permanent read access permission to the provider in your manifest. You can then get the contact's birthday information or his or her email address and then send the e-greeting.

   利用这个临时权限访问Contact Provider.

Using another application 启动有访问权限的第3方应用

　　A simple way to allow the user to modify data to which you don't have access permissions is to activate an application that has permissions and let the user do the work there.

　　For example, the Calendar application accepts an ACTION_INSERT intent, which allows you to activate the application's insert UI. You can pass "extras" data in this intent, which the application uses to pre-populate the UI. Because recurring events have a complex syntax, the preferred way of inserting events into the Calendar Provider is to activate the Calendar app with an ACTION_INSERT and then let the user insert the event there.

Displaying data using a helper app

　　If your application does have access permissions, you still may want to use an intent to display data in another application. For example, the Calendar application accepts an ACTION_VIEW intent, which displays a particular date or event. This allows you to display calendar information without having to create your own UI. To learn more about this feature, see the Calendar Provider guide.

　　The application to which you send the intent doesn't have to be the application associated with the provider. For example, you can retrieve a contact from the Contact Provider, then send an ACTION_VIEW intent containing the content URI for the contact's image to an image viewer.