What You'll Learn
How to use Android's file storage options: internal storage, scoped external storage, and Storage Access Framework.
Storage Types
| Type | API | Permission |
|---|---|---|
| Internal | context.filesDir | None |
| External (app) | getExternalFilesDir() | None |
| User files | SAF OpenDocument | None |
| Gallery | MediaStore | None (Android 10+) |
Internal Storage
// Write
context.openFileOutput("data.txt", Context.MODE_PRIVATE).use {
it.write(content.toByteArray())
}
// Read
context.openFileInput("data.txt").bufferedReader().use { it.readText() }
SAF — File Picker
val openLauncher = rememberLauncherForActivityResult(
ActivityResultContracts.OpenDocument()
) { uri -> uri?.let { readTextFromUri(context, it) } }
Button(onClick = { openLauncher.launch(arrayOf("text/*")) }) {
Text("Open File")
}
MediaStore — Save to Gallery
val values = ContentValues().apply {
put(MediaStore.Images.Media.DISPLAY_NAME, "photo.png")
put(MediaStore.Images.Media.MIME_TYPE, "image/png")
put(MediaStore.Images.Media.RELATIVE_PATH, Environment.DIRECTORY_PICTURES)
}
val uri = resolver.insert(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, values)
Summary
- Internal storage for app-private data
- External app-specific dirs need no permissions
- SAF for user-driven file operations
- MediaStore for shared media
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