When you want to access data in a content provider, you use the ContentResolver object in your application's Context to communicate with the provider as a client.
The ContentResolver object communicates with the provider object, an instance of a class that implements ContentProvider. The provider object receives data requests from clients, performs the requested action, and returns the results. This object has methods that call identically-named methods in the provider object, an instance of one of the concrete subclasses of ContentProvider.
The ContentResolver methods provide the basic "CRUD" create, retrieve, update, and delete functions of persistent storage. A common pattern for accessing a ContentProvider from your UI uses a CursorLoader to run an asynchronous query in the background. This allows the UI to continue to be available to the user while the query is running. This pattern involves the interaction of a number of different objects, as well as the underlying storage mechanism, as illustrated in figure 2.
Figure 2. Interaction between ContentProvider, other classes, and storage. Note: To access a provider, your application usually has to request specific permissions in its manifest file. This development pattern is described in more detail in the section Content Provider Permissions. One of the built-in providers in the Android platform is the user dictionary, which stores the spellings of non-standard words that the user wants to keep.
Table 1 illustrates what the data might look like in this provider's table:. In table 1, each row represents an instance of a word that might not be found in a standard dictionary.
Each column represents some data for that word, such as the locale in which it was first encountered. The column headers are column names that are stored in the provider. To refer to a row's locale, you refer to its locale column. To get a list of the words and their locales from the User Dictionary Provider, you call ContentResolver.
The query method calls the ContentProvider. The following lines of code show a ContentResolver. Content URIs include the symbolic name of the entire provider its authority and a name that points to a table a path. When you call a client method to access a table in a provider, the content URI for the table is one of the arguments. The ContentResolver object parses out the URI's authority, and uses it to "resolve" the provider by comparing the authority to a system table of known providers.
The ContentResolver can then dispatch the query arguments to the correct provider. A provider usually has a path for each table it exposes. Many providers allow you to access a single row in a table by appending an ID value to the end of the URI.
You often use id values when you've retrieved a set of rows and then want to update or delete one of them. Note: The Uri and Uri. Builder classes contain convenience methods for constructing well-formed URI objects from strings. This section describes how to retrieve data from a provider, using the User Dictionary Provider as an example.
For the sake of clarity, the code snippets in this section call ContentResolver. In actual code, however, you should do queries asynchronously on a separate thread. One way to do this is to use the CursorLoader class, which is described in more detail in the Loaders guide. Also, the lines of code are snippets only; they don't show a complete application. To retrieve data from a provider, your application needs "read access permission" for the provider. When you specify this element in your manifest, you are in effect "requesting" this permission for your application.
When users install your application, they implicitly grant this request. To find the exact name of the read access permission for the provider you're using, as well as the names for other access permissions used by the provider, look in the provider's documentation. The role of permissions in accessing providers is described in more detail in the section Content provider permissions. The User Dictionary Provider defines the permission android.
The next step in retrieving data from a provider is to construct a query. This first snippet defines some variables for accessing the User Dictionary Provider:. The next snippet shows how to use ContentResolver. A provider client query is similar to an SQL query, and it contains a set of columns to return, a set of selection criteria, and a sort order.
The set of columns that the query should return is called a projection the variable mProjection. The expression that specifies the rows to retrieve is split into a selection clause and selection arguments. The selection clause is a combination of logical and Boolean expressions, column names, and values the variable mSelectionClause. If you specify the replaceable parameter? In the next snippet, if the user doesn't enter a word, the selection clause is set to null , and the query returns all the words in the provider.
If the user enters a word, the selection clause is set to UserDictionary. In this SQL statement, the actual column names are used instead of contract class constants. Since the selection clause is treated as an SQL statement, this might cause the provider to erase all of the tables in the underlying SQLite database unless the provider is set up to catch SQL injection attempts. To avoid this problem, use a selection clause that uses?
When you do this, the user input is bound directly to the query rather than being interpreted as part of an SQL statement. Instead of using concatenation to include the user input, use this selection clause:.
A selection clause that uses? The ContentResolver. A Cursor object provides random read access to the rows and columns it contains. Using Cursor methods, you can iterate over the rows in the results, determine the data type of each column, get the data out of a column, and examine other properties of the results. Some Cursor implementations automatically update the object when the provider's data changes, or trigger methods in an observer object when the Cursor changes, or both.
Note: A provider may restrict access to columns based on the nature of the object making the query. For example, the Contacts Provider restricts access for some columns to sync adapters, so it won't return them to an activity or service.
If no rows match the selection criteria, the provider returns a Cursor object for which Cursor. If an internal error occurs, the results of the query depend on the particular provider. It may choose to return null , or it may throw an Exception. Since a Cursor is a "list" of rows, a good way to display the contents of a Cursor is to link it to a ListView via a SimpleCursorAdapter.
The following snippet continues the code from the previous snippet. It creates a SimpleCursorAdapter object containing the Cursor retrieved by the query, and sets this object to be the adapter for a ListView :. Rather than simply displaying query results, you can use them for other tasks. For example, you can retrieve spellings from the user dictionary and then look them up in other providers.
To do this, you iterate over the rows in the Cursor :. Cursor implementations contain several "get" methods for retrieving different types of data from the object. For example, the previous snippet uses getString. They also have a getType method that returns a value indicating the data type of the column.
A provider's application can specify permissions that other applications must have in order to access the provider's data. These permissions ensure that the user knows what data an application will try to access. Based on the provider's requirements, other applications request the permissions they need in order to access the provider. End users see the requested permissions when they install the application.
If a provider's application doesn't specify any permissions, then other applications have no access to the provider's data, unless the provider is exported.
Additionally, components in the provider's application always have full read and write access, regardless of the specified permissions. As noted previously, the User Dictionary Provider requires the android.
The provider has the separate android. When the Android Package Manager installs the application, a user must approve all of the permissions the application requests. If the user approves all of them, Package Manager continues the installation; if the user doesn't approve them, Package Manager aborts the installation.
The impact of permissions on provider access is explained in more detail in the Security and permissions guide. In the same way that you retrieve data from a provider, you also use the interaction between a provider client and the provider's ContentProvider to modify data.
You call a method of ContentResolver with arguments that are passed to the corresponding method of ContentProvider. The provider and provider client automatically handle security and inter-process communication. To insert data into a provider, you call the ContentResolver.
This method inserts a new row into the provider and returns a content URI for that row. This snippet shows how to insert a new word into the User Dictionary Provider:. The data for the new row goes into a single ContentValues object, which is similar in form to a one-row cursor. The columns in this object don't need to have the same data type, and if you don't want to specify a value at all, you can set a column to null using ContentValues.
Providers usually use this value as the table's primary key. The content URI returned in newUri identifies the newly-added row, with the following format:. Most providers can detect this form of content URI automatically and then perform the requested operation on that particular row. To update a row, you use a ContentValues object with the updated values just as you do with an insertion, and selection criteria just as you do with a query.
The client method you use is ContentResolver. You only need to add values to the ContentValues object for columns you're updating. If you want to clear the contents of a column, set the value to null. The following snippet changes all the rows whose locale has the language "en" to a have a locale of null.
The return value is the number of rows that were updated:. You should also sanitize user input when you call ContentResolver. To learn more about this, read the section Protecting against malicious input. Deleting rows is similar to retrieving row data: you specify selection criteria for the rows you want to delete and the client method returns the number of deleted rows. The following snippet deletes rows whose appid matches "user".
The method returns the number of deleted rows. Content providers can offer many different data types. The User Dictionary Provider offers only text, but providers can also offer the following formats:. You can see the available data types by looking at the Cursor class "get" methods. The data type for each column in a provider is usually listed in its documentation.
The data types for the User Dictionary Provider are listed in the reference documentation for its contract class UserDictionary. Words contract classes are described in the section Contract Classes. You can also determine the data type by calling Cursor.
You can use the MIME type information to find out if your application can handle data that the provider offers, or to choose a type of handling based on the MIME type.
You usually need the MIME type when you are working with a provider that contains complex data structures or files. For example, the ContactsContract. 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 the file, we call the file provider which provide the URI to access the file. Add the following line of code in the Manifest file. There is a tag provider which help to restrict the application to access files of specified path mentioned in the resorce file i. In this you have to create the xml provide file which tell the path of image URI in android. Create a xml file and following lines of code. Hope this will help you.
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A content provider is a subclass of ContentProvider that supplies structured access to data managed by the application. Multiple authorities are listed by separating their names with a semicolon. To avoid conflicts, authority names should use a Java-style naming convention such as com. Typically, it's the name of the ContentProvider subclass that implements the provider There is no default. At least one authority must be specified.
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