java.lang.Object | |
↳ | android.content.ContentProvider |
Known Direct Subclasses |
Content providers are one of the primary building blocks of Android applications, providing
content to applications. They encapsulate data and provide it to applications through the single
ContentResolver
interface. A content provider is only required if you need to share
data between multiple applications. For example, the contacts data is used by multiple
applications and must be stored in a content provider. If you don't need to share data amongst
multiple applications you can use a database directly via
SQLiteDatabase
.
When a request is made via
a ContentResolver
the system inspects the authority of the given URI and passes the
request to the content provider registered with the authority. The content provider can interpret
the rest of the URI however it wants. The UriMatcher
class is helpful for parsing
URIs.
The primary methods that need to be implemented are:
onCreate()
which is called to initialize the providerquery(Uri, String[], String, String[], String)
which returns data to the callerinsert(Uri, ContentValues)
which inserts new data into the content providerupdate(Uri, ContentValues, String, String[])
which updates existing data in the content providerdelete(Uri, String, String[])
which deletes data from the content providergetType(Uri)
which returns the MIME type of data in the content providerData access methods (such as insert(Uri, ContentValues)
and
update(Uri, ContentValues, String, String[])
) may be called from many threads at once, and must be thread-safe.
Other methods (such as onCreate()
) are only called from the application
main thread, and must avoid performing lengthy operations. See the method
descriptions for their expected thread behavior.
Requests to ContentResolver
are automatically forwarded to the appropriate
ContentProvider instance, so subclasses don't have to worry about the details of
cross-process calls.
For more information about using content providers, read the Content Providers developer guide.
Nested Classes | |||||||||||
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ContentProvider.PipeDataWriter<T> | Interface to write a stream of data to a pipe. |
[Expand]
Inherited Constants | |||||||||||
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From interface
android.content.ComponentCallbacks2
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Public Constructors | |||||||||||
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Construct a ContentProvider instance.
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Public Methods | |||||||||||
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Override this to handle requests to perform a batch of operations, or the
default implementation will iterate over the operations and call
apply(ContentProvider, ContentProviderResult[], int) on each of them. | |||||||||||
After being instantiated, this is called to tell the content provider
about itself.
| |||||||||||
Override this to handle requests to insert a set of new rows, or the
default implementation will iterate over the values and call
insert(Uri, ContentValues) on each of them. | |||||||||||
Call a provider-defined method.
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Implement this to handle requests to delete one or more rows.
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Retrieves the Context this provider is running in.
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Return the path-based permissions required for read and/or write access to
this content provider.
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Return the name of the permission required for read-only access to
this content provider.
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Called by a client to determine the types of data streams that this
content provider supports for the given URI.
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Implement this to handle requests for the MIME type of the data at the
given URI.
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Return the name of the permission required for read/write access to
this content provider.
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Implement this to handle requests to insert a new row.
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Called by the system when the device configuration changes while your
component is running.
This method is always called on the application main thread, and must
not perform lengthy operations.
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Implement this to initialize your content provider on startup.
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This is called when the overall system is running low on memory, and
would like actively running process to try to tighten their belt.
This method is always called on the application main thread, and must
not perform lengthy operations.
| |||||||||||
Called when the operating system has determined that it is a good
time for a process to trim unneeded memory from its process.
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This is like
openFile(Uri, String) , but can be implemented by providers
that need to be able to return sub-sections of files, often assets
inside of their .apk. | |||||||||||
Override this to handle requests to open a file blob.
| |||||||||||
A helper function for implementing
openTypedAssetFile(Uri, String, Bundle) , for
creating a data pipe and background thread allowing you to stream
generated data back to the client. | |||||||||||
Called by a client to open a read-only stream containing data of a
particular MIME type.
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Implement this to handle query requests from clients.
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Implement this to handle query requests from clients with support for cancellation.
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Implement this to shut down the ContentProvider instance.
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Implement this to handle requests to update one or more rows.
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Protected Methods | |||||||||||
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Returns true if this instance is a temporary content provider.
| |||||||||||
Convenience for subclasses that wish to implement
openFile(Uri, String)
by looking up a column named "_data" at the given URI. | |||||||||||
Change the path-based permission required to read and/or write data in
the content provider.
| |||||||||||
Change the permission required to read data from the content
provider.
| |||||||||||
Change the permission required to read and write data in the content
provider.
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[Expand]
Inherited Methods | |||||||||||
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From class
java.lang.Object
| |||||||||||
From interface
android.content.ComponentCallbacks
| |||||||||||
From interface
android.content.ComponentCallbacks2
|
Construct a ContentProvider instance. Content providers must be
declared
in the manifest, accessed with ContentResolver
, and created
automatically by the system, so applications usually do not create
ContentProvider instances directly.
At construction time, the object is uninitialized, and most fields and
methods are unavailable. Subclasses should initialize themselves in
onCreate()
, not the constructor.
Content providers are created on the application main thread at application launch time. The constructor must not perform lengthy operations, or application startup will be delayed.
Override this to handle requests to perform a batch of operations, or the
default implementation will iterate over the operations and call
apply(ContentProvider, ContentProviderResult[], int)
on each of them.
If all calls to apply(ContentProvider, ContentProviderResult[], int)
succeed
then a ContentProviderResult
array with as many
elements as there were operations will be returned. If any of the calls
fail, it is up to the implementation how many of the others take effect.
This method can be called from multiple threads, as described in
Processes
and Threads.
operations | the operations to apply |
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OperationApplicationException | thrown if any operation fails. |
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After being instantiated, this is called to tell the content provider about itself.
context | The context this provider is running in |
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info | Registered information about this content provider |
Override this to handle requests to insert a set of new rows, or the
default implementation will iterate over the values and call
insert(Uri, ContentValues)
on each of them.
As a courtesy, call notifyChange()
after inserting.
This method can be called from multiple threads, as described in
Processes
and Threads.
uri | The content:// URI of the insertion request. |
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values | An array of sets of column_name/value pairs to add to the database. |
Call a provider-defined method. This can be used to implement interfaces that are cheaper and/or unnatural for a table-like model.
method | method name to call. Opaque to framework, but should not be null. |
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arg | provider-defined String argument. May be null. |
extras | provider-defined Bundle argument. May be null. |
Implement this to handle requests to delete one or more rows.
The implementation should apply the selection clause when performing
deletion, allowing the operation to affect multiple rows in a directory.
As a courtesy, call notifyDelete()
after deleting.
This method can be called from multiple threads, as described in
Processes
and Threads.
The implementation is responsible for parsing out a row ID at the end
of the URI, if a specific row is being deleted. That is, the client would
pass in content://contacts/people/22
and the implementation is
responsible for parsing the record number (22) when creating a SQL statement.
uri | The full URI to query, including a row ID (if a specific record is requested). |
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selection | An optional restriction to apply to rows when deleting. |
SQLException |
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Retrieves the Context this provider is running in. Only available once
onCreate()
has been called -- this will return null in the
constructor.
Return the path-based permissions required for read and/or write access to this content provider. This method can be called from multiple threads, as described in Processes and Threads.
Return the name of the permission required for read-only access to this content provider. This method can be called from multiple threads, as described in Processes and Threads.
Called by a client to determine the types of data streams that this content provider supports for the given URI. The default implementation returns null, meaning no types. If your content provider stores data of a particular type, return that MIME type if it matches the given mimeTypeFilter. If it can perform type conversions, return an array of all supported MIME types that match mimeTypeFilter.
uri | The data in the content provider being queried. |
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mimeTypeFilter | The type of data the client desires. May be a pattern, such as *\/* to retrieve all possible data types. |
Implement this to handle requests for the MIME type of the data at the
given URI. The returned MIME type should start with
vnd.android.cursor.item
for a single record,
or vnd.android.cursor.dir/
for multiple items.
This method can be called from multiple threads, as described in
Processes
and Threads.
Note that there are no permissions needed for an application to access this information; if your content provider requires read and/or write permissions, or is not exported, all applications can still call this method regardless of their access permissions. This allows them to retrieve the MIME type for a URI when dispatching intents.
uri | the URI to query. |
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Return the name of the permission required for read/write access to this content provider. This method can be called from multiple threads, as described in Processes and Threads.
Implement this to handle requests to insert a new row.
As a courtesy, call notifyChange()
after inserting.
This method can be called from multiple threads, as described in
Processes
and Threads.
uri | The content:// URI of the insertion request. |
---|---|
values | A set of column_name/value pairs to add to the database. |
Called by the system when the device configuration changes while your component is running. Note that, unlike activities, other components are never restarted when a configuration changes: they must always deal with the results of the change, such as by re-retrieving resources.
At the time that this function has been called, your Resources object will have been updated to return resource values matching the new configuration. This method is always called on the application main thread, and must not perform lengthy operations.
The default content provider implementation does nothing. Override this method to take appropriate action. (Content providers do not usually care about things like screen orientation, but may want to know about locale changes.)
newConfig | The new device configuration. |
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Implement this to initialize your content provider on startup. This method is called for all registered content providers on the application main thread at application launch time. It must not perform lengthy operations, or application startup will be delayed.
You should defer nontrivial initialization (such as opening,
upgrading, and scanning databases) until the content provider is used
(via query(Uri, String[], String, String[], String)
, insert(Uri, ContentValues)
, etc). Deferred initialization
keeps application startup fast, avoids unnecessary work if the provider
turns out not to be needed, and stops database errors (such as a full
disk) from halting application launch.
If you use SQLite, SQLiteOpenHelper
is a helpful utility class that makes it easy to manage databases,
and will automatically defer opening until first use. If you do use
SQLiteOpenHelper, make sure to avoid calling
getReadableDatabase()
or
getWritableDatabase()
from this method. (Instead, override
onOpen(SQLiteDatabase)
to initialize the
database when it is first opened.)
This is called when the overall system is running low on memory, and would like actively running process to try to tighten their belt. While the exact point at which this will be called is not defined, generally it will happen around the time all background process have been killed, that is before reaching the point of killing processes hosting service and foreground UI that we would like to avoid killing.
Applications that want to be nice can implement this method to release any caches or other unnecessary resources they may be holding on to. The system will perform a gc for you after returning from this method. This method is always called on the application main thread, and must not perform lengthy operations.
The default content provider implementation does nothing. Subclasses may override this method to take appropriate action.
Called when the operating system has determined that it is a good time for a process to trim unneeded memory from its process. This will happen for example when it goes in the background and there is not enough memory to keep as many background processes running as desired. You should never compare to exact values of the level, since new intermediate values may be added -- you will typically want to compare if the value is greater or equal to a level you are interested in.
To retrieve the processes current trim level at any point, you can
use ActivityManager.getMyMemoryState(RunningAppProcessInfo)
.
level | The context of the trim, giving a hint of the amount of
trimming the application may like to perform. May be
TRIM_MEMORY_COMPLETE , TRIM_MEMORY_MODERATE ,
TRIM_MEMORY_BACKGROUND , TRIM_MEMORY_UI_HIDDEN ,
TRIM_MEMORY_RUNNING_CRITICAL , TRIM_MEMORY_RUNNING_LOW ,
or TRIM_MEMORY_RUNNING_MODERATE .
|
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This is like openFile(Uri, String)
, but can be implemented by providers
that need to be able to return sub-sections of files, often assets
inside of their .apk.
This method can be called from multiple threads, as described in
Processes
and Threads.
If you implement this, your clients must be able to deal with such
file slices, either directly with
openAssetFileDescriptor(Uri, String)
, or by using the higher-level
ContentResolver.openInputStream
or ContentResolver.openOutputStream
methods.
If you are implementing this to return a full file, you
should create the AssetFileDescriptor with
UNKNOWN_LENGTH
to be compatible with
applications that can not handle sub-sections of files.
uri | The URI whose file is to be opened. |
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mode | Access mode for the file. May be "r" for read-only access, "w" for write-only access (erasing whatever data is currently in the file), "wa" for write-only access to append to any existing data, "rw" for read and write access on any existing data, and "rwt" for read and write access that truncates any existing file. |
FileNotFoundException | Throws FileNotFoundException if there is no file associated with the given URI or the mode is invalid. |
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SecurityException | Throws SecurityException if the caller does not have permission to access the file. |
Override this to handle requests to open a file blob.
The default implementation always throws FileNotFoundException
.
This method can be called from multiple threads, as described in
Processes
and Threads.
This method returns a ParcelFileDescriptor, which is returned directly to the caller. This way large data (such as images and documents) can be returned without copying the content.
The returned ParcelFileDescriptor is owned by the caller, so it is their responsibility to close it when done. That is, the implementation of this method should create a new ParcelFileDescriptor for each call.
uri | The URI whose file is to be opened. |
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mode | Access mode for the file. May be "r" for read-only access, "rw" for read and write access, or "rwt" for read and write access that truncates any existing file. |
FileNotFoundException | Throws FileNotFoundException if there is no file associated with the given URI or the mode is invalid. |
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SecurityException | Throws SecurityException if the caller does not have permission to access the file. |
A helper function for implementing openTypedAssetFile(Uri, String, Bundle)
, for
creating a data pipe and background thread allowing you to stream
generated data back to the client. This function returns a new
ParcelFileDescriptor that should be returned to the caller (the caller
is responsible for closing it).
uri | The URI whose data is to be written. |
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mimeType | The desired type of data to be written. |
opts | Options supplied by caller. |
args | Your own custom arguments. |
func | Interface implementing the function that will actually stream the data. |
FileNotFoundException |
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Called by a client to open a read-only stream containing data of a
particular MIME type. This is like openAssetFile(Uri, String)
,
except the file can only be read-only and the content provider may
perform data conversions to generate data of the desired type.
The default implementation compares the given mimeType against the
result of getType(Uri)
and, if the match, simple calls
openAssetFile(Uri, String)
.
See ClipData
for examples of the use and implementation
of this method.
uri | The data in the content provider being queried. |
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mimeTypeFilter | The type of data the client desires. May be a pattern, such as *\/*, if the caller does not have specific type requirements; in this case the content provider will pick its best type matching the pattern. |
opts | Additional options from the client. The definitions of these are specific to the content provider being called. |
FileNotFoundException | Throws FileNotFoundException if there is no file associated with the given URI or the mode is invalid. |
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SecurityException | Throws SecurityException if the caller does not have permission to access the data. |
IllegalArgumentException | Throws IllegalArgumentException if the content provider does not support the requested MIME type. |
Implement this to handle query requests from clients. This method can be called from multiple threads, as described in Processes and Threads.
Example client call:
// Request a specific record. Cursor managedCursor = managedQuery( ContentUris.withAppendedId(Contacts.People.CONTENT_URI, 2), projection, // Which columns to return. null, // WHERE clause. null, // WHERE clause value substitution People.NAME + " ASC"); // Sort order.Example implementation:
// SQLiteQueryBuilder is a helper class that creates the // proper SQL syntax for us. SQLiteQueryBuilder qBuilder = new SQLiteQueryBuilder(); // Set the table we're querying. qBuilder.setTables(DATABASE_TABLE_NAME); // If the query ends in a specific record number, we're // being asked for a specific record, so set the // WHERE clause in our query. if((URI_MATCHER.match(uri)) == SPECIFIC_MESSAGE){ qBuilder.appendWhere("_id=" + uri.getPathLeafId()); } // Make the query. Cursor c = qBuilder.query(mDb, projection, selection, selectionArgs, groupBy, having, sortOrder); c.setNotificationUri(getContext().getContentResolver(), uri); return c;
uri | The URI to query. This will be the full URI sent by the client; if the client is requesting a specific record, the URI will end in a record number that the implementation should parse and add to a WHERE or HAVING clause, specifying that _id value. |
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projection | The list of columns to put into the cursor. If null all columns are included. |
selection | A selection criteria to apply when filtering rows. If null then all rows are included. |
selectionArgs | You may include ?s in selection, which will be replaced by the values from selectionArgs, in order that they appear in the selection. The values will be bound as Strings. |
sortOrder | How the rows in the cursor should be sorted. If null then the provider is free to define the sort order. |
Implement this to handle query requests from clients with support for cancellation. This method can be called from multiple threads, as described in Processes and Threads.
Example client call:
// Request a specific record. Cursor managedCursor = managedQuery( ContentUris.withAppendedId(Contacts.People.CONTENT_URI, 2), projection, // Which columns to return. null, // WHERE clause. null, // WHERE clause value substitution People.NAME + " ASC"); // Sort order.Example implementation:
// SQLiteQueryBuilder is a helper class that creates the // proper SQL syntax for us. SQLiteQueryBuilder qBuilder = new SQLiteQueryBuilder(); // Set the table we're querying. qBuilder.setTables(DATABASE_TABLE_NAME); // If the query ends in a specific record number, we're // being asked for a specific record, so set the // WHERE clause in our query. if((URI_MATCHER.match(uri)) == SPECIFIC_MESSAGE){ qBuilder.appendWhere("_id=" + uri.getPathLeafId()); } // Make the query. Cursor c = qBuilder.query(mDb, projection, selection, selectionArgs, groupBy, having, sortOrder); c.setNotificationUri(getContext().getContentResolver(), uri); return c;
If you implement this method then you must also implement the version of
query(Uri, String[], String, String[], String)
that does not take a cancellation
signal to ensure correct operation on older versions of the Android Framework in
which the cancellation signal overload was not available.
uri | The URI to query. This will be the full URI sent by the client; if the client is requesting a specific record, the URI will end in a record number that the implementation should parse and add to a WHERE or HAVING clause, specifying that _id value. |
---|---|
projection | The list of columns to put into the cursor. If null all columns are included. |
selection | A selection criteria to apply when filtering rows. If null then all rows are included. |
selectionArgs | You may include ?s in selection, which will be replaced by the values from selectionArgs, in order that they appear in the selection. The values will be bound as Strings. |
sortOrder | How the rows in the cursor should be sorted. If null then the provider is free to define the sort order. |
cancellationSignal | A signal to cancel the operation in progress, or null if none.
If the operation is canceled, then OperationCanceledException will be thrown
when the query is executed. |
Implement this to shut down the ContentProvider instance. You can then invoke this method in unit tests.
Android normally handles ContentProvider startup and shutdown automatically. You do not need to start up or shut down a ContentProvider. When you invoke a test method on a ContentProvider, however, a ContentProvider instance is started and keeps running after the test finishes, even if a succeeding test instantiates another ContentProvider. A conflict develops because the two instances are usually running against the same underlying data source (for example, an sqlite database).
Implementing shutDown() avoids this conflict by providing a way to terminate the ContentProvider. This method can also prevent memory leaks from multiple instantiations of the ContentProvider, and it can ensure unit test isolation by allowing you to completely clean up the test fixture before moving on to the next test.
Implement this to handle requests to update one or more rows.
The implementation should update all rows matching the selection
to set the columns according to the provided values map.
As a courtesy, call notifyChange()
after updating.
This method can be called from multiple threads, as described in
Processes
and Threads.
uri | The URI to query. This can potentially have a record ID if this is an update request for a specific record. |
---|---|
values | A Bundle mapping from column names to new column values (NULL is a valid value). |
selection | An optional filter to match rows to update. |
Returns true if this instance is a temporary content provider.
Convenience for subclasses that wish to implement openFile(Uri, String)
by looking up a column named "_data" at the given URI.
uri | The URI to be opened. |
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mode | The file mode. May be "r" for read-only access, "w" for write-only access (erasing whatever data is currently in the file), "wa" for write-only access to append to any existing data, "rw" for read and write access on any existing data, and "rwt" for read and write access that truncates any existing file. |
FileNotFoundException |
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Change the path-based permission required to read and/or write data in the content provider. This is normally set for you from its manifest information when the provider is first created.
permissions | Array of path permission descriptions. |
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Change the permission required to read data from the content provider. This is normally set for you from its manifest information when the provider is first created.
permission | Name of the permission required for read-only access. |
---|
Change the permission required to read and write data in the content provider. This is normally set for you from its manifest information when the provider is first created.
permission | Name of the permission required for read/write access. |
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