Content Provider in Jetpack

Content Providers in Android

A Content Provider is a component in Android used to manage access to a central repository of data. It allows applications to share data with each other in a structured and secure way. Content providers enable CRUD (Create, Read, Update, Delete) operations on app data.

Key Features of Content Providers

1. Data Sharing: Allows sharing of data between different applications securely.
2. Structured Access: Provides a standardized way to query and manipulate data using URIs.
3. Integration: Works with ContentResolver for data access and manipulation.

Content Provider Components

1. URI (Uniform Resource Identifier): A unique identifier for the data (e.g., content://com.example.provider/users).
2. ContentResolver: Used by client applications to interact with the content provider.
3. Cursor: A pointer to the result set of a query.

Creating a Content Provider

To create a custom content provider:

1. Extend the ContentProvider class.
2. Implement its abstract methods:

• onCreate(): Initialize resources.
• query(): Retrieve data.
• insert(): Insert new data.
• update(): Update existing data.
• delete(): Delete data.
• getType(): Return the MIME type of data.

Example: Custom Content Provider

1. ContentProvider Class

class MyContentProvider : ContentProvider() {

    companion object {
        const val AUTHORITY = "com.example.provider"
        val CONTENT_URI: Uri = Uri.parse("content://$AUTHORITY/users")
        const val TABLE_NAME = "users"
    }

    private lateinit var database: SQLiteDatabase

    override fun onCreate(): Boolean {
        val dbHelper = MyDatabaseHelper(context!!)
        database = dbHelper.writableDatabase
        return true
    }

    override fun query(
        uri: Uri,
        projection: Array<out String>?,
        selection: String?,
        selectionArgs: Array<out String>?,
        sortOrder: String?
    ): Cursor? {
        return database.query(TABLE_NAME, projection, selection, selectionArgs, null, null, sortOrder)
    }

    override fun insert(uri: Uri, values: ContentValues?): Uri? {
        val id = database.insert(TABLE_NAME, null, values)
        context?.contentResolver?.notifyChange(uri, null)
        return ContentUris.withAppendedId(CONTENT_URI, id)
    }

    override fun update(uri: Uri, values: ContentValues?, selection: String?, selectionArgs: Array<out String>?): Int {
        val rowsUpdated = database.update(TABLE_NAME, values, selection, selectionArgs)
        context?.contentResolver?.notifyChange(uri, null)
        return rowsUpdated
    }

    override fun delete(uri: Uri, selection: String?, selectionArgs: Array<out String>?): Int {
        val rowsDeleted = database.delete(TABLE_NAME, selection, selectionArgs)
        context?.contentResolver?.notifyChange(uri, null)
        return rowsDeleted
    }

    override fun getType(uri: Uri): String? {
        return "vnd.android.cursor.dir/$TABLE_NAME"
    }
}

2. Database Helper

class MyDatabaseHelper(context: Context) : SQLiteOpenHelper(context, "MyDatabase", null, 1) {

    override fun onCreate(db: SQLiteDatabase) {
        db.execSQL("CREATE TABLE users (_id INTEGER PRIMARY KEY, name TEXT, email TEXT)")
    }

    override fun onUpgrade(db: SQLiteDatabase, oldVersion: Int, newVersion: Int) {
        db.execSQL("DROP TABLE IF EXISTS users")
        onCreate(db)
    }
}

3. Manifest Declaration

Add the content provider in the AndroidManifest.xml file.

<provider
    android:name=".MyContentProvider"
    android:authorities="com.example.provider"
    android:exported="true"
    android:grantUriPermissions="true" />

Using a Content Provider

1. Insert Data

val values = ContentValues().apply {
    put("name", "John Doe")
    put("email", "john.doe@example.com")
}

val uri = contentResolver.insert(MyContentProvider.CONTENT_URI, values)
Log.d("ContentProvider", "Inserted URI: $uri")

2. Query Data

val cursor = contentResolver.query(
    MyContentProvider.CONTENT_URI,
    arrayOf("_id", "name", "email"), // Columns
    null, // Selection
    null, // Selection Args
    null  // Sort Order
)

cursor?.use {
    while (it.moveToNext()) {
        val id = it.getInt(it.getColumnIndex("_id"))
        val name = it.getString(it.getColumnIndex("name"))
        val email = it.getString(it.getColumnIndex("email"))
        Log.d("ContentProvider", "User: $id, $name, $email")
    }
}

3. Update Data

val values = ContentValues().apply {
    put("email", "new.email@example.com")
}

val rowsUpdated = contentResolver.update(
    MyContentProvider.CONTENT_URI,
    values,
    "name = ?", // Selection
    arrayOf("John Doe") // Selection Args
)

Log.d("ContentProvider", "Rows Updated: $rowsUpdated")

4. Delete Data

val rowsDeleted = contentResolver.delete(
    MyContentProvider.CONTENT_URI,
    "name = ?", // Selection
    arrayOf("John Doe") // Selection Args
)

Log.d("ContentProvider", "Rows Deleted: $rowsDeleted")

Built-in Content Providers

Android includes several built-in content providers for common data types:

1. Contacts: ContactsContract
2. Media Store: MediaStore
3. Settings: Settings.System

Example: Querying contacts:

val cursor = contentResolver.query(
    ContactsContract.Contacts.CONTENT_URI,
    null, null, null, null
)

cursor?.use {
    while (it.moveToNext()) {
        val name = it.getString(it.getColumnIndex(ContactsContract.Contacts.DISPLAY_NAME))
        Log.d("Contacts", "Name: $name")
    }
}

Best Practices

1. Secure Data Access: Use permissions or implement validation to prevent unauthorized access.
2. Minimize Resource Usage: Optimize queries and limit the amount of data returned.
3. Use URIs: Define consistent URI structures for easy data manipulation.