如何在单独的活动中从一个活动修改ArrayList

Question

How do i add more Cars to my ArrayList<Car> from a separate Activity ?

Because I have something like this :

 private List<Car> getData() {

 List<Car> cars = new ArrayList<Car>();

cars.add(new Car("Dodge", "Viper"));

cars.add(new Car("Chevrolet", "Corvette"));

cars.add(new Car("Aston Martin", "Vanquish"));

cars.add(new Car("Lamborghini", "Diablo"));

cars.add(new Car("Ford", "Pinto"));

return cars;

}

But cars are only example, I have textswitcher in one application and I want to get text from textswitcher and place it as new item in other Activity with listview.

Answer 1

Just make your List a class variable and have an addCar function

public void addCar(String make,String model){
      cars.add(new Car(make,model));
}

and change getData()

    private List<Car> getData() {

            addCar("Dodge", "Viper");
            addCar("Chevrolet", "Corvette");
            etc...

        return cars;

    }

and in your other Activity just call addCar(make,model)

Answer 2

Put cars into intent, which starts second Activity with putExtra() . Then retrieve it with getExtra() and add the cars you want.

Answer 3

There is no guarantee that the other Activity will exist in memory once you leave it (as the system may destroy it if memory resources become low). You should save your data to persistent storage (ie a database or SharedPreferences ) or pass the data as an Intent extra instead.

Answer 4

Basically you are going to need to pass the object to the other Activity for modification using Intents . HOWEVER , this seems very wrong . I would suggest re-thinking how you are adding Cars to your ArrayList outside of the Activity .

As Harmeet Singh mentioned, you might want to look into creating a sqlite table that will hold all your Cars . Then you can have your ListView have a CursorAdapter that is looking at that table. This will allow you add Cars from anywhere and will be MUCH more flexible and better practice.

Here are two posts that discuss passing the objects as Intents to your other Activity BUT again, i do not suggest you continue down this road to implement what you are asking. Go with sqlite and a database table.

1. How to pass object from one activity to another in Android
2. How do I pass data between activities in Android?

Answer 5

I would suggest you should use database like sqllite or to share a common resource like a xml file or any for permanent storage , this is not the way to make storage, as this type of storage is volatile .

All your data will go clean if memory clears in any case.

have a look android persistent storage