How do I append text to existing text file? - kotlin

Question

When saving the text file it is being saved for example in the Documents/ folder. I'm aware of that I need to use append to add new line of text to that existing file but I am not entirely sure how and where to add this line of code and check that file exists.
This is the current code that is handling saving the file.
...
save.setOnClickListener {
saveFile()
}
}
private fun saveFile() {
val fileIntent = Intent(Intent.ACTION_CREATE_DOCUMENT).apply {
addCategory(Intent.CATEGORY_OPENABLE)
type = "text/plain"
putExtra(Intent.EXTRA_TITLE, "measurements.txt")
// Optionally, specify a URI for the directory that should be opened in
// the system file picker before your app creates the document.
//putExtra(DocumentsContract.EXTRA_INITIAL_URI, pickerInitialUri)
}
saveLauncher.launch(fileIntent)
}
private var saveLauncher = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result ->
if (result.resultCode == Activity.RESULT_OK) {
val uri = result.data?.data
try {
val outputStream = uri?.let { contentResolver.openOutputStream(it) }
outputStream?.write(getMeasurement?.toByteArray())
outputStream?.close()
} catch (e: Exception) {
Toast.makeText(this, "Error is ${e.localizedMessage}", Toast.LENGTH_SHORT).show()
}
}
}

Answer 1

You can use a Writer to append text. Also, you should not put your close call inside the try block, or it could get skipped and you won't release the file. close should go in a finally block, but it's easier to use use { } instead.
When you open an output stream from the content resolver, you can specify write and append mode by passing "wa" as the second argument. See here and here in the documentation.
openOutputStream throws an exception if the file doesn't already exist. If you want to create a file if it doesn't exist yet, you'll need to add that logic.
I like to exit early from a function rather than nest everything in an if-statement, so I rearranged it that way in my example, but you don't have to do that.
private var saveLauncher = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result ->
val uri = result.data?.data
val content = getMeasurement
if (result.resultCode != Activity.RESULT_OK || uri == null || content == null) {
return#registerForActivityResult
}
try {
contentResolver.openOutputStream(uri, "wa")
.writer().use { it.write(content) }
} catch (e: Exception) {
Toast.makeText(this, "Error is ${e.localizedMessage}", Toast.LENGTH_SHORT).show()
}
}