Question

I am working on a project that involves me having to share an array list of objects with all of the activities that make up the application. Until recently I was passing the list between activities by implementing the parcelable interface. An example of this is seen below:

MenuItem class:

ublic class MenuItem implements Parcelable {

private String name;
private double price;
private int qty;
private String info;

public MenuItem(String name, double price) {
    super();
    this.name = name;
    this.price = price;
}
public MenuItem() {
    // TODO Auto-generated constructor stub
}
public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}
public double getPrice() {
    return price;
}
public void setPrice(double price) {
    this.price = price;
}

public int getQty() {
    return qty;
}
public void setQty(int qty) {
    this.qty = qty;
}
public String getInfo() {
    return info;
}
public void setInfo(String info) {
    this.info = info;
}
@Override
public String toString() {
    return name;
}


//Parcelable methods.
public static final Parcelable.Creator<MenuItem> CREATOR = new Parcelable.Creator<MenuItem>() {

    @Override
    public MenuItem createFromParcel(Parcel source) {
        return new MenuItem(source);
    }

    @Override
    public MenuItem[] newArray(int size) {
        return new MenuItem[size];
    }
};

public MenuItem(Parcel source) {
    this();
    readFromParcel(source);
}

private void readFromParcel(Parcel source) {
    name = source.readString();
    price = source.readDouble();
}

@Override
public int describeContents() {
    return 0;
}

@Override
public void writeToParcel(Parcel dest, int flags) {
    dest.writeString(name);
    dest.writeDouble(price);
}

}

Order class – which I would change to be the Singleton (holds list of menu items)

public class Order implements Parcelable {


private int covers;
private int table;
private ArrayList<MenuItem> items;


public Order(){
    super();
    this.items = new ArrayList<MenuItem>();

}

public static final Parcelable.Creator<Order> CREATOR = new Parcelable.Creator<Order>() {

    @Override
    public Order createFromParcel(Parcel source) {
        return new Order(source);
    }

    @Override
    public Order[] newArray(int size) {
        return new Order[size];
    }


};

public Order(int covers, int table) {
    super();
    this.covers = covers;
    this.table = table;
    this.items = new ArrayList<MenuItem>();
}

public int getCovers() {
    return covers;
}

public void setCovers(int covers) {
    this.covers = covers;
}

public int getTable() {
    return table;
}

public void setTable(int table) {
    this.table = table;
}

public ArrayList<MenuItem> getItems() {
    return items;
}

public void setItems(ArrayList<MenuItem> items) {
    this.items = items;
}

//add to order
public void addToOrder(MenuItem m){
    items.add(m);
}

//remove from order
public void removeFromOrder(MenuItem m){
    items.remove(m);
}

public Order(Parcel source) {
    this();
    readFromParcel(source);
}

@Override
public int describeContents() {
    // TODO Auto-generated method stub
    return 0;
}

@Override
public void writeToParcel(Parcel dest, int flags) {
    // TODO Auto-generated method stub
    dest.writeInt(covers);
    dest.writeInt(table);
    dest.writeTypedList(items);

}

private  void readFromParcel(Parcel source) {
    // TODO Auto-generated method stub
    covers = source.readInt();
    table = source.readInt();
    items = new ArrayList<MenuItem>();
    source.readTypedList(items,  MenuItem.CREATOR);

}

}

This is how I pass the data between activities:

myOrderBtn.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            Toast.makeText(v.getContext(), "myOrderBtn", Toast.LENGTH_SHORT).show();
            Intent i = new Intent(v.getContext(), ViewOrderActivity.class);
            i.putExtra("data", order);
            if(!saved){
            saveOrderState();
            }
            startActivity(i);

        }
    });

and retrieve this way:

public void getOrderData(){
    Intent i = getIntent();
    if(i != null && i.hasExtra("data")){
        order = i.getParcelableExtra("data");
        Toast.makeText(this.getApplicationContext(), "STARTERS recieved order object, covers: " + order.getCovers() + " table no: " + order.getTable() + " order size: " + order.getItems().size(), Toast.LENGTH_SHORT).show();

        if(order.getItems().size() == 0){
            //Toast.makeText(this.getApplicationContext(), "No items added to your order...", Toast.LENGTH_SHORT).show();
        }else{
            for(int j = 0; j != order.getItems().size(); j++){
                dishItems.add(order.getItems().get(j));
            }
        }

        saved = false;

    }
}

Today I learned about the use of a Singleton for global access to data, and I am wondering would it be a good idea to switch to this style of data access? It seems easier to control and a lot tidier with respects to the code.

I’d be interested to see what your opinions on this are. This link here is the pattern I would like to implement:

http://www.devahead.com/blog/2011/06/extending-the-android-application-class-and-dealing-with-singleton/

I should mention, the project is part of my studies in my course. I have to submit my code in a few weeks time, so I am looking for the best way to make it more efficient. So please let me know if you see anything that looks wrong as well!

Answer 1

There is very little reason to use Parcelable to move an object around inside a single Linux process. I suggest making your menu a static member of a custom Application object, something like this:

public class MyApplication extends Application {
    private static final List<MenuItem> menu;
    static {
        List<MenuItem> l = new ArrayList<MenuItems>();
        l.add(new MenuItem(...));
        ...
        menu = Collections.unmodifiableList(l);
    }

    ...

    public List<MenuItems> getMenu() { return menu; }

    ....

}

Make sure that the list is immutable, so that you don’t have to worry about concurrency issues.

In your manifest:

<application
    android:name=".MyApplication"

… and access it with:

List<MenuItem> menu = ((MyApplication) getApplication()).getMenu();