How to properly transfer a large amount of data, such…

Passing large amounts of data, such as images, directly through Intent is not recommended due to the size limit on data serialized during transmission (usually a few hundred kilobytes or megabytes). Transferring too much data can lead to a TransactionTooLargeException.

Proper approaches:

Save data to a file and pass the file path in Intent.

Save the image to a temporary file.
Pass the URI or file path in the Extra of the intent.
The receiving activity reads the file from the received path.

// Saving in the first activity
val imageUri: Uri = saveImageToFile(bitmap) // Function to save Bitmap to file and return Uri
val intent = Intent(this, SecondActivity::class.java)
intent.putExtra("image_uri", imageUri.toString())
startActivity(intent)

// Reading in the second activity
val imageUriString = intent.getStringExtra("image_uri")
if (imageUriString != null) {
    val imageUri = Uri.parse(imageUriString)
    val bitmap = loadImageFromFile(imageUri) // Function to load Bitmap from Uri
    imageView.setImageBitmap(bitmap)
}

Use Singleton or global data storage.

Place data in a Singleton object or a separate class accessible from anywhere in the app.
No need to pass data between activities, just access the Singleton to get the data.

// Global object, e.g., in Application class or a separate singleton
object DataHolder {
    var bitmap: Bitmap? = null
}

// In the first activity
DataHolder.bitmap = bitmap

// In the second activity
val bitmap = DataHolder.bitmap
imageView.setImageBitmap(bitmap)
DataHolder.bitmap = null // Clear after use if needed

Consider the app's lifecycle and activity recreation.

Use a database (Room) or data storage (e.g., SharedPreferences, though not ideal for images).

Save the image (possibly as a byte array) in the database.
Pass the database record ID via Intent.
The receiving activity reads the image from the database using the ID.

// Saving in the first activity (pseudo-code for Room)
val imageEntity = ImageEntity(imageData = bitmapToByteArray(bitmap))
val imageId = imageDatabase.imageDao().insertImage(imageEntity)
val intent = Intent(this, SecondActivity::class.java)
intent.putExtra("image_id", imageId)
startActivity(intent)

// Reading in the second activity (pseudo-code for Room)
val imageId = intent.getLongExtra("image_id", -1)
if (imageId != -1L) {
    val imageEntity = imageDatabase.imageDao().getImageById(imageId)
    if (imageEntity != null) {
        val bitmap = byteArrayToBitmap(imageEntity.imageData)
        imageView.setImageBitmap(bitmap)
    }
}

Use Shared ViewModel in Navigation Component.

If using Navigation Component, you can use a shared ViewModel tied to the navigation graph or activity.
Data is placed in the ViewModel of one activity and accessible from another.

// In ViewModel
class SharedViewModel : ViewModel() {
    val imageBitmap = MutableLiveData<Bitmap>()
}

// In the first activity (using Navigation Component)
private val sharedViewModel: SharedViewModel by activityViewModels() // or by navGraphViewModels(R.id.nav_graph)
sharedViewModel.imageBitmap.value = bitmap

// In the second activity
private val sharedViewModel: SharedViewModel by activityViewModels() // or by navGraphViewModels(R.id.nav_graph)
sharedViewModel.imageBitmap.observe(viewLifecycleOwner) { bitmap ->
    if (bitmap != null) {
        imageView.setImageBitmap(bitmap)
    }
}

The method choice depends on the use case, data size, and app complexity. For images, saving to a file (and passing the URI) or using Singleton/ViewModel are often the most suitable and efficient solutions.

How to properly transfer a large amount of data, such as an image, between activities in Android?