Question

I’m experimenting with android, and I got to the point where I want to save something to internal memory and read from it, but I’m kind of stuck. I found this article http://developer.android.com/guide/topics/data/data-storage.html#filesInternal and as it suggested I created dummy method :

public void test(){

    String FILENAME = "hello_file";
    String string = "hello world!";

    FileOutputStream fos = openFileOutput(FILENAME, Context.MODE_PRIVATE);
    fos.write(string.getBytes());
    fos.close();

}

Which always throws NullPointerException, anyone knows what I’m missing?Maybe some permission in Androidmanifest.xml ?

QUESTION UPDATE:

FileOutputStream fos = openFileOutput(FILENAME, Context.MODE_PRIVATE);

Above line trows NPE. My class is abstract and its extending Activity, I don’t know if that is relevant or not.

Stack trace :

01-29 22:30:44.575: ERROR/TEST(458): java.lang.NullPointerException
01-29 22:30:44.575: ERROR/TEST(458): java.lang.RuntimeException: java.lang.NullPointerException

It seems that any IO operation throws NPE, I tried this as well :

try {
            File myDir = new File(getFilesDir().getAbsolutePath());
            String s = "";

            FileWriter fw = new FileWriter(myDir + "/Test.txt");
            fw.write("Hello World");
            fw.close();

            BufferedReader br = new BufferedReader(new FileReader(myDir + "/Test.txt"));
            s = br.readLine();

            // Set TextView text here using tv.setText(s);

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

File myDir = new File(getFilesDir().getAbsolutePath());

Throws NPE, I even added

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

into Androidmanifest.xml

I’ve made method and pass in Context ctx, but my ctx ends up null, how can I get this variable? set it to which value ?

Answer 1

From extensive googling I found that you need to pass Context to your method, which you initialize in onCreate method Context ctx = getApplicationContext(); and you pass it to the rest of the application which needs it.