How to read and write txt files in android in kotl

问题:

I'm still pretty much a beginner in kotlin and android studio. I can access most of the android widgets but I cannot access files and so far I managed to come across only the following code which does not work. The app crashes...

var recordsFile = File("/LET/Records.txt")
recordsFile.appendText("record goes here")

It will be much appreciated if I can also know how to create the file at a specific location. Like at root directory or internal storage or in a file in the internal storage. Thanks..

回答1:

I just want to add on to TpoM6oH's answer. When working with Files, you may be not guaranteed with 100% success on the file operations you intend. So, it is a better practice to try and catch for exceptions like filenotfoundexception etc. and take a due care about the flow of program control.

To create a file at the external storage in Android, you can get the location using

Environment.getExternalStorageDirectory()

and check if the location exists. If it does not, create one and continue creating and writing your file using Kotlin

val sd_main = File(Environment.getExternalStorageDirectory()+"/yourlocation")
var success = true
if (!sd_main.exists())
    success = sd_main.mkdir()

if (success) {
    val sd = File("filename.txt")

    if (!sd.exists())
        success = sd.mkdir()

    if (success) {
        // directory exists or already created
        val dest = File(sd, file_name)
        try {
            // response is the data written to file
            PrintWriter(dest).use { out -> out.println(response) }
        } catch (e: Exception) {
            // handle the exception
        }
    }
} else {
    // directory creation is not successful
}

Hope this helps.

回答2:

You need to use internal or external storage directory for your file.

Internal:

val path = context.getFilesDir()

External:

val path = context.getExternalFilesDir(null)

If you want to use external storage you'll need to add a permission to the manifest:

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

Create your directory:

val letDirectory = File(path, "LET")
letDirectory.mkdirs()

Then create your file:

val file = File(letDirectory, "Records.txt")

Then you can write to it:

FileOutputStream(file).use {
    it.write("record goes here".getBytes())
}

or just

file.appendText("record goes here")

And read:

val inputAsString = FileInputStream(file).bufferedReader().use { it.readText() }

回答3:

Kotlin has made file reading/writing quite simple.

For reading/writing to internal storage:

context.openFileOutput(filename, Context.MODE_PRIVATE).use {
    it.write(message.toByteArray())
}
.
.
.
val file = File(context.filesDir, "myfile.txt")
val contents = file.readText() // Read file

For reading/writing to external storage:

val file = File(Environment.getExternalStorageDirectory()+"/path/to/myfile.txt")
file.writeText("This will be written to the file!")
.
.
.
val contents = file.readText() // Read file

回答4:

In 5 lines: create file to internal directory if not exists, write to file, read file

val file = File(ctx.filesDir, FILE_NAME)
file.createNewFile()
file.appendText("record goes here")
val readResult = FileInputStream(file).bufferedReader().use { it.readText() }
println("readResult=$readResult")