Android 内部存储：文件一旦被读取即为空

Question

So I am trying to save a HashMap as a JSON file into the internal storage of the app. This works well, as I can see in the device file explorer, everything is saved properly. When I then restart the app and read from the file it also works BUT after this one time reading the file is empty. Completely empty not even some "{}" when you save an empty JSON object.

public void writeNetworks(FileOutputStream fos) {
    Log.d(TAG, "writeNetworks");

    Gson gson = new GsonBuilder().create();
    String json = gson.toJson(networks);

    Log.d(TAG, json);

    PrintWriter out = new PrintWriter(new OutputStreamWriter(fos));
    out.println(json);
    out.flush();
    out.close();
}

public void readNetworks(FileInputStream fis) {
    Log.d(TAG, "readNetworks");

    try {
        BufferedReader in = new BufferedReader(new InputStreamReader(fis));
        StringBuilder json = new StringBuilder();
        String line;
        while((line = in.readLine()) != null ) {
            json.append(line);
        }
        in.close();

        Log.d(TAG, json.toString());

        Gson gson = new GsonBuilder().create();
        Type typeOfHashMap = new TypeToken<Map<String, WrcUser>>() { }.getType();
        networks = gson.fromJson(json.toString(), typeOfHashMap);
    } catch (IOException e) {
        e.printStackTrace();
    }
}

Any ideas?

Answer 1

I actually found a way for it to work... I am now calling writeNetowrks(..) in the onStop() method of my activity. It seems to work consistent so far.