Question 127023 in Android Studio Question posted in
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Android Studio – How do I read from a Object ArrayList File to a Object Arralist?

I’ve been trying to do this for a while but I didn’t find any solution.

I’m working on a shopping list app for android and I have an arraylist of items. I want to write it into a file which will be read everytime the app is opened, to save changes of it. I have a method to write the arraylist, which is this one:

File path = getApplicationContext().getFilesDir();
    try {
        FileOutputStream fos = new FileOutputStream("output");
        ObjectOutputStream oos = new ObjectOutputStream(fos);
        oos.writeObject(items);
        oos.close();
    } catch(Exception ex) {
        ex.printStackTrace();
    }

However I tried many things to read the file and none seem to work. What can I do?

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2

Answers


  1. Chosen as BEST ANSWER
    0

    Found the solution. I read the arraylist with this:

    public void loadContent(){

        File path = getApplicationContext().getFilesDir();
    File readFile = new File(path,"output.txt");
    

    try {

        FileInputStream readData = new FileInputStream(readFile);
        ObjectInputStream readStream = new ObjectInputStream(readData);
        ArrayList<Item> aux = (ArrayList<Item>) readStream.readObject();
        readStream.close();
        items = aux;

        adapter = new ArrayAdapter<>(this,android.R.layout.simple_list_item_multiple_choice,items);

        elementsList.setAdapter(adapter);
    } catch (Exception e) {
        e.printStackTrace();
    }


}

  2. 0

    In java, you can use a try-witch-resource block.This makes sure that you close the file of something goes wrong. I use BufferReader when I want to read from a while.

    In this code snippet, I store each line in an arraylist:

    ArrayList<String> lines;

    Then you iterate through the file:

    try(BufferedReader reader = Files.newBufferedReader(path)) {
        String line;
        while((line = reader.readLine())!= null){ //while there is a next line..
            lines.add(line);
        }
    } catch (IOException e) {
        /* File does not exits. */
        throw new IllegalArgumentException("File not found");
    }

    I recommend watching a youtube video, or reading on the javadoc for the buffer reader.

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