Develop Reference

Android, how to prevent internal storage files to be deleted when the app is uninstalled

I'm developing an app which stores few setting in two .xml files, saved on internal storage. I need to save them in there, so please don't answer me "Save them on SD-cards".
I try to uninstall an then re-install (from Android Studio) my app to see if the android:allowBackup="true" works also for internal stored file but the answer was no.
Is this because I done the re-install from the IDE or I need to add some code somewhere?
Thanks for help.

Starting API level 29 there is the "hasFragileUserData" manifest flag
The documentation states that
If true the user is prompted to keep the app's data on uninstall.
May be a boolean value, such as "true" or "false".
Sample code:
<application
....
android:hasFragileUserData="true">

You can save those file using Environment.getExternalStorageDirectory() This stores on the external storage device. Dont get confused with the term external storage as the SD card. SD card is the secondary external storage. But Environment.getExternalStorageDirectory() returns top-level directory of the primary external storage of your device which is basically a non removable storage.
So the file path can be /storage/emulated/0/YOURFOLDER/my.xml
So even if you uninstall the app, these files will not get deleted.
You can use this snippet to create a file in your primary external storage:
private final String fileName = "note.txt";
private void writeFile() {
File extStore = Environment.getExternalStorageDirectory();
// ==> /storage/emulated/0/note.txt
String path = extStore.getAbsolutePath() + "/" + fileName;
Log.i("ExternalStorageDemo", "Save to: " + path);
String data = editText.getText().toString();
try {
File myFile = new File(path);
myFile.createNewFile();
FileOutputStream fOut = new FileOutputStream(myFile);
OutputStreamWriter myOutWriter = new OutputStreamWriter(fOut);
myOutWriter.append(data);
myOutWriter.close();
fOut.close();
Toast.makeText(getApplicationContext(), fileName + " saved", Toast.LENGTH_LONG).show();
} catch (Exception e) {
e.printStackTrace();
}
}
Don't forget to add below permission in Android Manifest
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
You can then read that file as below:
private void readFile() {
File extStore = Environment.getExternalStorageDirectory();
// ==> /storage/emulated/0/note.txt
String path = extStore.getAbsolutePath() + "/" + fileName;
Log.i("ExternalStorageDemo", "Read file: " + path);
String s = "";
String fileContent = "";
try {
File myFile = new File(path);
FileInputStream fIn = new FileInputStream(myFile);
BufferedReader myReader = new BufferedReader(
new InputStreamReader(fIn));
while ((s = myReader.readLine()) != null) {
fileContent += s + "\n";
}
myReader.close();
this.textView.setText(fileContent);
} catch (IOException e) {
e.printStackTrace();
}
Toast.makeText(getApplicationContext(), fileContent, Toast.LENGTH_LONG).show();
}

Where does the file get saved using "File file = new file(filename)" in Android

I am writing an android application. In the MainActivity.java, I created a method to write and then read contents from a file. These code runs successfully I and can store the data in a file named abc.txt, but I cannot find the written file in ES File Explorer.
public void writeInIt(View view) {
try {
String Message = editText.getText().toString();
final File myFile = new File("abc.txt");
if (!myFile.exists()) {myFile.createNewFile(); }
FileOutputStream outputStream = new FileOutputStream(myFile);
outputStream.write(Message.getBytes());
outputStream.close();
editText.setText("");
Toast.makeText(getApplicationContext(), "Message Saved", Toast.LENGTH_LONG).show();
} catch (IOException e) {
e.printStackTrace();
}
}
Where does it save the file? Why I can't I search it through the File Explorer?
Ref to "http://developer.android.com/reference/java/io/File.html", if i include path, it will definitely store in that path location. However, if I not locate the dir, it can still store in device, but where does the file actually save???

"File file = new file(filename)"
this code does not save anything, it only cretes a class wrapper for file or director path. The closest method to actually create file would be to use file.createNewFile method.
There is guide for writing files from google: Saving Files
[edit]
following code generates exception "open failed: EROFS (Read-only file system)":
File fl = new File("test12.txt");
try {
fl.createNewFile();
} catch (IOException e) {
e.printStackTrace();
}

In Android manifest:
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
this is the code :
public void generateNoteOnSD(String sFileName, String sBody){
try
{
File root = new File(Environment.getExternalStorageDirectory(), "Notes");
if (!root.exists()) {
root.mkdirs();
}
File gpxfile = new File(root, sFileName);
FileWriter writer = new FileWriter(gpxfile);
writer.append(sBody);
writer.flush();
writer.close();
Toast.makeText(this, "Saved", Toast.LENGTH_SHORT).show();
}
catch(IOException e)
{
e.printStackTrace();
importError = e.getMessage();
iError();
}
}

You can find this file in device manager.
Click your device (file symbol)
/data/user/0/com.example.myapplication/files and than follow this path

How to create files to a specific folder in android application?

In my application, I want to create a text file in the cache folder and first what I do is create a folder in the cache directory.
File myDir = new File(getCacheDir(), "MySecretFolder");
myDir.mkdir();
Then I want to create a text file in that created folder using the following code that doesn't seem to make it there. Instead, the code below creates the text file in the "files" folder that is in the same directory as the "cache" folder.
FileOutputStream fOut = null;
try {
fOut = openFileOutput("secret.txt",MODE_PRIVATE);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
String str = "data";
try {
fOut.write(str.getBytes());
} catch (IOException e) {
e.printStackTrace();
}
try {
fOut.close();
} catch (IOException e) {
e.printStackTrace();
}
SO my question is, how do I properly designate the "MySecretFolder" to make the text file in?
I have tried the following:
"/data/data/com.example.myandroid.cuecards/cache/MySecretFolder", but it crashes my entire app if I try that. How should I properly save the text file in the cache/MySecretFolder?

use getCacheDir(). It returns the absolute path to the application-specific cache directory on the filesystem. Then you can create your directory
File myDir = new File(getCacheDir(), "folder");
myDir.mkdir();
Please try this maybe helps you.
Ok, If you want to create the TextFile in Specific Folder then You can try to below code.
try {
String rootPath = Environment.getExternalStorageDirectory()
.getAbsolutePath() + "/MyFolder/";
File root = new File(rootPath);
if (!root.exists()) {
root.mkdirs();
}
File f = new File(rootPath + "mttext.txt");
if (f.exists()) {
f.delete();
}
f.createNewFile();
FileOutputStream out = new FileOutputStream(f);
out.flush();
out.close();
} catch (Exception e) {
e.printStackTrace();
}

Just change
fOut = openFileOutput("secret.txt",MODE_PRIVATE);
to
fOut = openFileOutput(myDir+"/secret.txt",MODE_PRIVATE);
This will make secret.txt under MySecretFolder

getPrivateDir will create a folder in your private area (Context.MODE_WORLD_WRITEABLE- use what suits you from Context.MODE_...)
public File getPrivateDir(String name)
{
return context.getDir(name, Context.MODE_WORLD_WRITEABLE);
}
openPrivateFileInput will create a file if it doesn't exist in your private folder in files directory and return a FileInputStream :
/data/data/your.packagename/files
Your application private folder is in
/data/data/your.packagename
public FileInputStream openPrivateFileInput(String name) throws FileNotFoundException
{
return context.openFileInput(name);
}
If you package name is uno.due.com your app private folder is:
/data/data/uno.due.com
All directories underneath are weather created by you or by android for you. When you create a file as above it will go under:
/data/data/uno.due.com/files

Simple and easy code to create folder, file and write/append into the file
try {
String path = Environment.getExternalStorageDirectory().getAbsolutePath() + "/newfoldername/"; // it will return root directory of internal storage
File root = new File(path);
if (!root.exists()) {
root.mkdirs(); // create folder if not exist
}
File file = new File(rootPath + "log.txt");
if (!file.exists()) {
file.createNewFile(); // create file if not exist
}
BufferedWriter buf = new BufferedWriter(new FileWriter(file, true));
buf.append("hi this will write in to file");
buf.newLine(); // pointer will be nextline
buf.close();
}
catch (Exception e) {
e.printStackTrace();
}
NOTE: It needs the Android External Storage Permission so add below line in AndroidManifest.xml
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>

Android: problems creating a file

I'm writing an Android application in which I want to create text files in a particular folder and afterwards I want to read the files from my device.
I'm doing this way:
File sd = Environment.getExternalStorageDirectory();
File f;
FileWriter fw = null;
String path = sd.getAbsolutePath() + "/Samples/";
f = new File(path+File.separator+"filename.txt");
if (!f.exists())
{
f.mkdirs();//Creates the directory named by this file, creating missing parent directories if necessary
try
{
f.createNewFile();
//fw = new FileWriter(f, true);
}
catch (IOException e)
{
Log.e("ERROR","Exception while creating file:"+e.toString());
}
The problem is that in this way I create another folder instead of a text file. What can I do? Thanks

Instead of:
f.mkdirs();
do:
path.mkdirs();

I found the solution and I want to share it with you:
File sd = Environment.getExternalStorageDirectory();
File folder;
String path = sd.getAbsolutePath() ;
folder = new File(path, dirName);
if (!folder.exists()){
folder.mkdirs();}
try{
File file = new File(folder, fileName+".txt");
file.createNewFile();
} catch (IOException e) {
Log.e("ERROR", "Exception while creating file:" + e.toString());
}
I hope this could help other people having the same problem. Good luck

Create file from assets and get its path

I want to display a PDF stored in the assets folder using an external library. This library requires a path to a file.
I read that the pdf stored in the assets folder is not stored as a file. What I need is
Read the pdf-file from the assets into a (temporary) file object
get the path of that object for the external pdf-viewer-library
What I got so far is the following:
stream = getAssets().open("excerpt.pdf");
BufferedReader reader = new BufferedReader(
new InputStreamReader(stream));
I'm not really sure what to do next unfortunately...
EDIT:
I tried the following code:
private void copyAssets() {
AssetManager assetManager = getAssets();
String[] files = null;
try {
files = assetManager.list("");
} catch (IOException e) {
Log.e("tag", "Failed to get asset file list.", e);
}
for(String filename : files) {
InputStream in = null;
OutputStream out = null;
try {
in = assetManager.open(filename);
String dirout= Environment.getExternalStorageDirectory().getAbsolutePath() + "/X/Y/Z/" ;
File outFile = new File(dirout, filename);
out = new FileOutputStream(outFile);
copyFile(in, out);
in.close();
in = null;
out.flush();
out.close();
out = null;
} catch(IOException e) {
Log.e("tag", "Failed to copy asset file: " + filename, e);
}
}
}
...
I am getting an exception in "out = new FileOutputStream(outFile);" (no such file or directory). I thought the code create a file there?

Does the directory exists?
If not, it will send an IOException.
Just to make sure, try this approach:
final File directory = new File("/sdcard/X/Y/Z/");
if (!directory.exists()) {
directory.mkdirs();
}
It will create the parent directories if they don't exist. If they exist, it will return false and it will NOT delete the content in it. After this, just continue the same way you were doing it.
File outFile = new File(directory, filename);
Don't forget to add the permissions to your AndroidManifest!
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

Copy the file to a public location that other applications can access using a process similar to that described in this question.
Keep a reference to the external file you created for launching your Intent(Intent.ACTION_VIEW).
Build an Intent to view your pdf, ex:
public void viewPdf(File YOUR_PUBLIC_FILE_FROM_STEP_1) {
PackageManager packageManager = getPackageManager();
Intent viewPdf = new Intent(Intent.ACTION_VIEW);
viewPdf.setType("application/pdf");
List<ResolveInfo> list =packageManager.queryIntentActivities(viewPdf,PackageManager.MATCH_DEFAULT_ONLY);
// Check available PDF viewers on device
if (list.size() > 0) {
Intent from_external_app = new Intent(Intent.ACTION_VIEW);
from_external_app.setDataAndType(Uri.fromFile(YOUR_PUBLIC_FILE_FROM_STEP_1),
"application/pdf");
from_external_app.setFlags(Intent.FLAG_ACTIVITY_NO_HISTORY);
startActivity(from_external_app);
}