Using Singleton methods in activities (Android)

Question

So I have been working on this android project in Android Studio where I let users create to-do lists. It's a class assignment and I have to work with a Singleton. I have been reading a lot of info and questions/answers about it but it has only made me progressively more confused.

In my MainActivity I tried to call the method ReadTitlesFromFile , but I get the errors:

Modifier 'public' not allowed here

and

Inner classes cannot have static declarations

Even though the code is exactly the same as the example that I found somewhere. Can somebody help me with fixing the error?

This is my Singleton:

public class ToDoManagerSingleton {
private ArrayList<ToDoList> listTitles;

// One single instance for the entire app
private static ToDoManagerSingleton ourInstance = new ToDoManagerSingleton();

// Constructor
private ToDoManagerSingleton() {
    // Empty ArrayList with in it the different lists
    listTitles = new ArrayList<ToDoList>();
}

// Method to get the one single instance
public static ToDoManagerSingleton getInstance() {
    return ourInstance;
}

// Getter and setter
public void setListTitles (ArrayList listTitlesArg){
    listTitles = listTitlesArg;
}

public ArrayList getListTitles(){
    return listTitles;
}

// Add new title to list
public void AddNewTitle(ToDoList title){
    listTitles.add(title);
}

// Write list titles to a file
public void WriteListTitlesToFile (Context context){
    PrintStream outstream = null;
    try{
        outstream = new PrintStream(context.openFileOutput("titlesfile.txt", Context.MODE_PRIVATE));
        for (ToDoList listTitle : listTitles) {
            outstream.println(listTitle);
        }
    }
    catch (FileNotFoundException e){
        e.printStackTrace();
    }
}

// Read titlesfile.txt
public void ReadTitlesFromFile(Context context){
    try {
        FileInputStream inStream = context.openFileInput("titlesfile.txt");
        InputStreamReader inReader = new InputStreamReader(inStream);
        BufferedReader bufferedReader = new BufferedReader(inReader);
        StringBuilder sBuilder = new StringBuilder();
        String line;
        while ((line = bufferedReader.readLine()) != null){
            sBuilder.append(line).append("\n");
        }
    }
    catch (FileNotFoundException e){
        e.printStackTrace();
    }
    catch (IOException e){
        e.printStackTrace();
    }
}

// Read itemsfile.txt
public void ReadItemsFromFile(Context context){
    try {
        FileInputStream inStream = context.openFileInput("itemsfile.txt");
        InputStreamReader inReader = new InputStreamReader(inStream);
        BufferedReader bufferedReader = new BufferedReader(inReader);
        StringBuilder sBuilder = new StringBuilder();
        String line;
        while ((line = bufferedReader.readLine()) != null){
            sBuilder.append(line).append("\n");
        }
    }
    catch (FileNotFoundException e){
        e.printStackTrace();
    }
    catch (IOException e){
        e.printStackTrace();
    }
}

}

And this is the MainActivity class:

public class MainActivity extends AppCompatActivity {

ListView showSavedFilesListview;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // Initialize listview
    showSavedFilesListview = (ListView) findViewById(R.id.ListView1);

    // Read titles from titlesfile.txt
    public class ReadTitles {
        public static void main (Context context) {
            ToDoManagerSingleton tmp = ToDoManagerSingleton.getInstance();
            tmp.ReadTitlesFromFile(Context context);
        }
    }

}

I'm sorry if this is a stupid question, or if it has already been asked before, but I'm new to programming and all the info tends to confuse me.

Answer 1

You have placed a class inside a method. That's why you are getting the error: "Modifier 'public' not allowed here"

You don't need the class ReadTitles anyway; and even if you do use it, remove the the static modifier from the main method.

Simply, instead of this:

// Read titles from titlesfile.txt
public class ReadTitles {
    public static void main (Context context) {
        ToDoManagerSingleton tmp = ToDoManagerSingleton.getInstance();
        tmp.ReadTitlesFromFile(Context context);
    }
}

put this:

// Read titles from titlesfile.txt
ToDoManagerSingleton tmp = ToDoManagerSingleton.getInstance();
tmp.ReadTitlesFromFile(this); // use the Activity context

Answer 2

As previously mentioned, you are attempting to declare a class of type ReadTitles within the onCreate method. You cannot do this.

Instead of:

public class ReadTitles {
    public static void main (Context context) {
        ToDoManagerSingleton tmp = ToDoManagerSingleton.getInstance();
        tmp.ReadTitlesFromFile(Context context);
    }
}

You can simply call your Singletons instance within onCreate . However, you need to obtain the application Context before you can call your ReadTitlesFromFile method. Presently, you're attempting to explicitly declare the type when passing the parameter to the ReadTitlesFromFile . You do not do this, as it will result in a compiler error. Instead, use the getApplicationContext() method to obtain the Context . See below:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // Initialize listview
    showSavedFilesListview = (ListView) findViewById(R.id.ListView1);

    // Read titles from titlesfile.txt
    ToDoManagerSingleton tmp = ToDoManagerSingleton.getInstance();
    Context context = getApplicationContext();
    tmp.ReadTitlesFromFile(context);
}