无法写入文件 - 为什么？

Question

I am attempting to save to long term file storage in android as well as create a new file in the process. This code keeps crashing with minimal helpful logcat.

Thanks.

public void save (String text) {
    FileOutputStream fos = null;
    try {
        fos = openFileOutput("logfile.txt", MODE_PRIVATE);
        fos.write(text.getBytes());
    } catch (FileNotFoundException e)
    {} catch (IOException e) {
        e.printStackTrace();
    } finally {
        if(fos != null)
        {
            try {
                fos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

I expect it to create a file called logfile.txt and print text to it but instead it crashes.

Answer 1

You need the file write permission in the manifest and ask for it (again) during runtime (as a pop-up). This is assuming you use external storage. Did you do this?

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

if (ContextCompat.checkSelfPermission(getActivity(),  Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
                            ActivityCompat.requestPermissions(getActivity(), new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 0x11);
                    } else Log.d("TAG", "permission already granted");

Answer 2

Try something alike this, in order to get a FileOutputStream from a File in tmp / private storage:

// File file = File.createTempFile("logfile", ".txt");
File file = new File(getFilesDir(), "logfile.txt");
FileOutputStream fos = new FileOutputStream(file);

The resulting path should be /data/data/tld.domain.package/files/logfile.txt .

file.getAbsolutePath() has the value.

See Save a file on internal storage .