将自定义对象保存到SD卡（Android）

Question

I'm exploring saving internally versus saving on the sdcard. Currently, I'm trying to save a custom object (DummyTwice) on the sdcard, like so:

            String root = (Environment.getExternalStorageDirectory().toString());
            File dir = new File(root + PUB_EXT_DIR);
            dir.mkdirs();
            File file = new File(dir,FILE_NAME);

            try {

                DummyTwice dt = new DummyTwice(textEnter.getText().toString());
                FileOutputStream os = new FileOutputStream(file);
                ObjectOutputStream oos = new ObjectOutputStream(os);
                oos.writeObject(dt);
                oos.close();
                os.close();

                Toast.makeText(v.getContext(),"Object Saved",Toast.LENGTH_SHORT).show();
                Toast.makeText(v.getContext(),file.getAbsolutePath(), Toast.LENGTH_LONG).show();

            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }

Execution stops at:

FileOutputStream os = new FileOutputStream(file);

Catching the exception:

FileNotFoundException e

What am I doing wrong? Relevant constants:

private final static String PUB_EXT_DIR = /data
private final static String FILE_NAME = /obj.dat 

Answer 1

you shouldn't write directly on the sdcard, and you should use

getExternalFilesDir(null)

instead of

Environment.getExternalStorageDirectory()

getExternalFilesDir(null) returns a private path on the sdcard for your Activity , like /sdcard/Android/data/package.your.app