Android：将数据从一个片段传递到另一个

Question

I wanted to pass arraylist of objects from one fragment to another i tried the following ways, wanted to know what are the pro's and con's of the following or is their any better approach

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First

public myFragment(ArrayList<E> myarray) {
super();        
this.myarray=myarray;
}

In the above code i created a constructor in the fragment class and used it to modify the arraylist but as i read from net this is not the best practice i searched for other's

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Second

public static myFragment newInstance(ArrayList<E> myarray1) {
   //        TODO Auto-generated constructor stub
    MyFragment myFragment=new MyFragment();
    myarray=myarray1;

}

here i created a static method which modify's the static arraylist myarray

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Third

public static myFragment newInstance(ArrayList<E> myarray1) {
   //        TODO Auto-generated constructor stub
    MyFragment myFragment=new MyFragment();
    Bundle bundle=new Bundle();
    bundle.putSerializable(TAG,myarray1);
    myFragment.setArguments(bundle);
    return myFragment;

}

In this code i created a Serializable arraylist and passed it to bundel then

myarray=(ArrayList<E>) bundle.getSerializable(TAG);

retrived the arraylist from bundle

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Fourth

the forth method which i got on net was using parcelable instead of Serializable but it was bit difficult to create a parcelable, if any one can share easy way to create a parceable as i have array list inside arraylist.

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So which of them is best approach or is their any better approach to send custom object from one fragment to another and what are their pro's and con's

Answer 1

1) You shouldn't ever override Fragment's constructor, it will cause unexpected crashes when system tries to recreate the fragment using the reflection.

2) You shouldn't use static ArrayList to hold the data because if you run into situation where you want to instatiate two fragments of the same kind, one will override the data from the second one

3) Serializable is acceptable way, but it's rather slow compared to the Parcelable since it uses reflection to restore your data

4) Parcelable is a way to go. It's a bit of pain to make your class Parcelable but it's way faster than option 3., and safer than options 1. and 2.

another ideas:

5) If you don't need to persist the data, you can construct a singleton class which will hold the data in the ArrayList , and you can access it from anywhere in the application

6) If you need to persist the data, you should store it in the database, and when you go from one Activity to antoher, or from one Fragment to another, you just pass the ID of the object in question and pull the data from DB.

Answer 2

I would suggest using the newInstance() static method as this is the way that Google suggests that you create fragments (see http://developer.android.com/guide/components/fragments.html ) and make sure you have a no args constructor. (also limitations of others as Tomislav Novoselec has said)

A nice way I've found to easily convert objects to implement the Parcelable interface is this Android studio plugin > android-parcelable-intellij-plugin . There is also a website to help you do it too if you prefer > parcelable.com

(Parcelable objects are also more efficient than serializable too I've been told, so use them were you can)