Develop Reference

How can I make my Android app read and write a .txt file?

I'm using Xamarin, C# and Monogame and I'm taking a fully-working Desktop game and porting it over to Android.
My problem is that I have this "Content folder" that you would always use in the Desktop version of the app. But I cannot access it or any other folder through the code directly using Android.
basicShader = new Effect(game1.GraphicsDevice,System.IO.File.ReadAllBytes("Content/TextureShader.mgfxo"));
This works just fine in the Desktop app but throws System.IO.DirectoryNotFoundException:'Could not find a part of the path "/Content/TextureShader.mgfxo".' on Android.
I'd like to mention that I already had the code and the project working perfectly when it was a desktop program. I also have a private class-level variable string[] list_of_files and in the constructor, I had the line list_of_files = Directory.GetFiles("./Content","*.txt");
This is for saving and loading player data. It may have been rudimentary but I had a fully functioning program that saved and loaded data on my computer. I am transitioning this program to be an Android app and this is the only part of the project that isn't working. When I run the code as it was originally written, I get "System.IO.DirectoryNotFoundException: 'Could not find a part of the path '/Content'.' ".
I've tried playing around with trying to read the contents of different folders.
I've messed around with different paths, including the Resources folder instead.
I added <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" /> to my manifest.
I know that I'm trying to access internal storage, not external, so I also tried <uses-permission android:name="android.permission.READ_INTERNAL_STORAGE" /> just to see if that might work.
Nothing works.
In another stack overflow post, a guy commented:
For the people who are facing NullPointerException - you are trying to access the files in the app's internal storage which are private sorry you can't do that. –
coderpc
Jun 23, 2017 at 16:00
I cannot imagine why this would be true. Why would a programmer not be able to write a program that can access it's own internal storage? That makes no sense to me. Obviously my app needs to be able to read and write it's own internal storage! And if this is true, then how else can I save persistent data on my phone? I don't want a database or a shared thingamabobber that uses key-value pairs, I have a self-made system that works as a text file and I want to continue to use it. I refuse to believe that an Android app can't keep track of a simple .txt file in one of it's own folders, that's just too hard for me to imagine. It can't be true.
I wanted to ask the commenter about his comment but Stack Overflow wouldn't let me because I don't have over 50xp.

Just like CommonsWare sayed, you can use the Intent.ActionOpenDocument to get the uri of the file. Such as
static readonly int READ_REQUEST_CODE = 1337;
Intent intent = new Intent(Intent.ActionOpenDocument);
intent.AddCategory(Intent.CategoryOpenable);
intent.SetType("*/*");
StartActivityForResult(intent, READ_REQUEST_CODE);
And override the OnActivityResult method:
if (requestCode == READ_REQUEST_CODE && resultCode == Result.Ok)
{
// The document selected by the user won't be returned in the intent.
// Instead, a URI to that document will be contained in the return intent
// provided to this method as a parameter. Pull that uri using "resultData.getData()"
if (data != null)
{
Android.Net.Uri uri = data.Data;
DocumentFile documentFile = DocumentFile.FromSingleUri(this.ApplicationContext,uri);
// Then you can operate the file with input and output stream
}
}
More information please check the simple on the github:
https://github.com/xamarin/monodroid-samples/blob/main/StorageClient/StorageClientFragment.cs
In addition, if you can ensure the file's path. You can use the StreamWriter and the StreamReader to write and read the file. Such as:
using (StreamWriter sw = new StreamWriter(path))
{
sw.WriteLine(content);
}
Furthermore, you can try to create the content folder and the txt file in the Android with the following code.
var filename1 = Android.App.Application.Context.GetExternalFilesDir(System.DateTime.Now.ToString("Content")).AbsolutePath;
var filename = System.IO.Path.Combine(filename1, "xxx.txt");
using (System.IO.FileStream os = new System.IO.FileStream(filename, System.IO.FileMode.Create))
{
}
The folder and the files created by this way belongs to the app and you can access it easily.
You can read the official document about the storage in the Android.
Link : https://developer.android.com/training/data-storage/shared/documents-files

Kotlin: How to create/append file (and share)

I have a list of arrays of data in my app that I would now like to write to a file (csv) and use a 3rd party app (such as email) to share this csv file. I have had no luck finding any helpful resources for creating, finding the file path for, and appending to a file in Kotlin. Does anyone have experience with this or have examples to point to? Just to get started I'm trying to write the header and close the file so I can see that it is correctly writing.
This is what I have for now:
val HEADER = "ID, time, PSI1, PSI2, PSI3, speed1, speed2, temp1, temp2"
val filename = "export.csv"
var fileOutStream : FileOutputStream = openFileOutput(filename,Context.MODE_PRIVATE)
try {
fileOutStream.write(HEADER.toByteArray())
fileOutStream.close()
}catch(e: Exception){
Log.i("TAG", e.toString())
}
It doesn't throw the exception, but I cannot find the file in the file system. I'm using a physical tablet for testing/debug. I've checked the com.... folder for my app.

I cannot find the file in the file system
Use Android Studio's Device File Explorer and look in /data/data/.../files/, where ... is your application ID.
Also, you can write your code a bit more concisely as:
try {
PrintWriter(openFileOutput(filename,Context.MODE_PRIVATE)).use {
it.println(HEADER)
}
} catch(e: Exception) {
Log.e("TAG", e.toString())
}
use() will automatically close the PrintWriter, and PrintWriter gives you a more natural API for writing out text.

It appears there are many ways to create a file and append to it, depending on the minimum API version you are developing for. I am using minimum Android API 22. The code to create/append a file is below:
val HEADER = "DATE,NAME,AMOUNT_DUE,AMOUNT_PAID"
var filename = "export.csv"
var path = getExternalFilesDir(null) //get file directory for this package
//(Android/data/.../files | ... is your app package)
//create fileOut object
var fileOut = File(path, filename)
//delete any file object with path and filename that already exists
fileOut.delete()
//create a new file
fileOut.createNewFile()
//append the header and a newline
fileOut.appendText(HEADER)
fileOut.appendText("\n")
/*
write other data to file
*/

openFileOutput() creates a private file, likely inside of app storage. These files are not browsable by default. If you want to create a file that can be browsed to, you'll need the WRITE_EXTERNAL_STORAGE permission, and will want to create files into a directory such as is provided by getExternalFilesDir()

How to pick file from external storage using file picker in Android

I am having a problem with selecting image file from external storage using file picker in Android. This question is the consequence of this question - No such file or diectory error in image file upload using Retrofit in Android. What my problem is opening and reading file from external storage on activity result. I want to convert result URI into File.
I read a pdf file from download folder on activity result
Uri bookUri = data.getData();
if(bookUri!=null)
{
String filePath = bookUri.toString();//bookUri.toString()
String mime = app.getMimeType(filePath);
if(mime!=null && !mime.isEmpty() && (mime.toLowerCase()=="application/pdf" || mime.toLowerCase()=="application/txt" || mime.toLowerCase()=="application/text"))
{
bookFile = new File(bookUri.getPath());
ivBookFile.setImageResource(R.drawable.book_selected);
}
else{
Toast.makeText(getBaseContext(),"Unable to process file you have chosen.",Toast.LENGTH_SHORT).show();
}
}
As you can see I used new File(bookUri.getPath()); to convert into File. The above code works well. It is working. The problem is now I am trying to open an image file in DCIM/Camera folder on activity result.
This is the code I used
Uri selectedImageUri = data.getData();
if(selectedImageUri!=null)
{
try{
bmpCoverImage = MediaStore.Images.Media.getBitmap(getContentResolver(), selectedImageUri);
imageFile = new File(selectedImageUri.getPath());
if(bmpCoverImage!=null)
{
ivCoverImage.setImageBitmap(bmpCoverImage);
}
}
catch (IOException e)
{
Toast.makeText(getBaseContext(),"An error occurred with the file selected",Toast.LENGTH_SHORT).show();
}
}
As you can see I used new File(selectedImageUri.getPath()); like I did in reading pdf file. This time the code is not working. When I do operation with the file like in previous question, it gives me error.
I used this way also
imageFile = new File(Environment.getExternalStorageDirectory(),selectedImageUri.getPath());
I got the same error. How can I open the image file correctly from external storage? How can I convert the chosen file URI from external storage into File?

I am having a problem with selecting image file from external storage using file picker in Android
If you are referring to the code that you are using in this question, you are not "using file picker". You are using ACTION_GET_CONTENT, which has never been a "file picker", nor will it ever be a "file picker".
I want to convert result URI into File.
Usually, that is not necessary. But, if that is what you want to do:
use ContentResolver and openInputStream() to get an InputStream on the content represented by the Uri
create a FileOutputStream on your desired file
use Java I/O to copy the bytes from the InputStream into the FileOutputStream
The above code works well. It is working.
It works for the small number of devices that you tested, for the specific activities that the user chose to handle the ACTION_GET_CONTENT request. It will not work on most Android devices, and it will not work in most circumstances. The only time that code will work is if the Uri has a file scheme. Most of the time, it will not. Instead, it will have a content scheme, representing content supplied by a ContentProvider.
Please how can I open the image file correctly from external storage?
If you wish to continue using ACTION_GET_CONTENT, please understand that this has nothing to do with external storage specifically. You are not getting a file, on external storage or elsewhere. You are getting a Uri. This is akin to a URL, such as the URL for this Web page. Just as a URL does not necessarily point to a file on your hard drive, a Uri does not necessarily point to a file on the filesystem. Use a ContentResolver and DocumentFile to work with the Uri and the content that it identifies.
If you want to always get files on external storage (and nowhere else), then use an actual file picker library.

Multiple file sharing intent crashes when launched from ES File Explorer

I've written a small file sharing program in android where user can select multiple files for sharing via my app, either from native Android gallery or some file manager (like ES File Explorer). To start with, I'm just displaying the selected file paths in a TextView of MainActivity. Here is my code snippet:
if (Intent.ACTION_SEND_MULTIPLE.equals(getIntent().getAction())
&& getIntent().hasExtra(Intent.EXTRA_STREAM)) {
ArrayList<Parcelable> list = getIntent()
.getParcelableArrayListExtra(Intent.EXTRA_STREAM);
for (Parcelable parcel : list) {
Uri uri = (Uri) parcel;
String sourcepath = getPath(uri);
filepathNameArray.add(sourcepath); //building file path name array from gallery
myTextView.append(sourcepath + "\n"); //displaying selected files' path in textView
}
}
The above code works fine when user selects multiple files from Gallery, but the app crashes when I select files (for sharing via my app) from ES File Explorer. Can anyone please suggest a workaround for this? Thanks for your help!

Setting Internal Read Write properties for an existing file

I'm having an issue with opening internal data files in native applications
Its properly important to point out that I'm fairly new to Android development but not new to programming
Setup
I have a mobile Air application which i am running on an Android device. To load PDF's/ play videos within the application I have written a native extension to load the files via their native application.
Problem
When testing the app i found that file's stored in the external storage were loading fine and files in the internal storage were presenting messages from the native applications like cannot play file or cannot open file.( files in internal storage are downloaded and saved on the Air application end ).
This lead me to think its the permission setup within Android.
I know that files within the internal storage are private by default
I have read how to write to a file setting its permission using openFileOutput
but as the file already exists this won't work. I could load the file in and spit it out again but this isn't ideal as will result in what might be unnecessary overhead.
I'm not sure how to proceed, do i need to set a manifest properties on the Air App side? Android App side? both sides? If so which one and where
Or is their a way to change it at run-time, i found the setReadable function but its at API level 9 and i am idealy aiming a little lower than that.
Any help is greatly appreciated
public static void openFile( Activity parentActivity, String filePath, String fileType, String mimeType ) {
//Create the file we are to create
File fileToOpen = new File(filePath);
//Check if the file exists
if( fileToOpen.exists() ) {
//The path of the file we want to open
Uri path = Uri.fromFile(fileToOpen);
//Create a new intent of the file we want to view
Intent intent = new Intent(Intent.ACTION_VIEW);
//Set the path and the mime type for the file
intent.setDataAndType(path, mimeType);
//Remove any other activities
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
//Check that its within the try and catch block
try {
//Open the file by stating a new activity
parentActivity.startActivity(intent);
}
catch (ActivityNotFoundException e) {
//Make a pop-up informing that we don't have an application to open the file
Toast.makeText( parentActivity,"No Application Available to View " + fileType,Toast.LENGTH_SHORT).show();
}
} else {
//Display an alert which will show that the file dosn't exist
Toast.makeText( parentActivity, fileType+" file dosn't exist", Toast.LENGTH_SHORT).show();
}
}