Android ContentProviders & MediaStore Architecture

A ContentProvider manages access to a centralized repository of data. In Android, each app runs in its own private sandbox with isolated storage. ContentProviders provide a standardized, secure mechanism for sharing data across process boundaries using standard Content URIs.

Content URI Structure

Just as a website is identified by an HTTP URL, data inside a ContentProvider is addressed via a Content URI:

content://com.veewom.android.provider/tutorials/42
  │                 │                      │      │
Scheme          Authority                 Path    ID

• Scheme: Always content:// for Android providers.
• Authority: A globally unique string (typically the package name + .provider).
• Path: Identifies the table or resource category (e.g., tutorials).
• ID: Optional primary key pointing to a specific row record.

Querying System Data via ContentResolver (MediaStore)

Android's system MediaStore provider manages photos, videos, and audio on the device. Here is how an app queries user photos:

import android.content.ContentUris
import android.provider.MediaStore
import android.net.Uri

data class MediaPhoto(val uri: Uri, val displayName: String, val size: Long)

fun queryRecentPhotos(context: Context): List<MediaPhoto> {
    val photoList = mutableListOf<MediaPhoto>()
    val projection = arrayOf(
        MediaStore.Images.Media._ID,
        MediaStore.Images.Media.DISPLAY_NAME,
        MediaStore.Images.Media.SIZE
    )
    val sortOrder = "${MediaStore.Images.Media.DATE_ADDED} DESC"

    context.contentResolver.query(
        MediaStore.Images.Media.EXTERNAL_CONTENT_URI,
        projection,
        null,
        null,
        sortOrder
    )?.use { cursor ->
        val idColumn = cursor.getColumnIndexOrThrow(MediaStore.Images.Media._ID)
        val nameColumn = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DISPLAY_NAME)
        val sizeColumn = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.SIZE)

        while (cursor.moveToNext()) {
            val id = cursor.getLong(idColumn)
            val name = cursor.getString(nameColumn)
            val size = cursor.getLong(sizeColumn)
            val contentUri = ContentUris.withAppendedId(
                MediaStore.Images.Media.EXTERNAL_CONTENT_URI, id
            )
            photoList.add(MediaPhoto(contentUri, name, size))
        }
    }
    return photoList
}