Fragment Management and Navigation (Delivery App)

Question

I am trying to build a delivery app. I have a list of products to choose from. After the user selects a product then he is lead to a series of stages to define extras and options of a certain product.

List of products:

Then, Lets say someone clicks on one of the products, we go to the controller FragmentActivity:

The subtotal at top and the button at the bottom of the page belongs to the fragment activity. Then I place a group of radio buttons at the center layout. Everything is fine till now. Click on the button leads for the replacement of the fragment:

Everything is beautiful until now. I can access the buttons and the subtotal through the fragments. However, if I press the back button on the device it leads me back to the list of products and not to the previous fragment. Even if I manage to go back to the previous fragment it would lose the radiobutton selection as well.

Then the next fragment is a calculation of the products and its extras:

When I press the button, I just use finish() in the fragment and it leads me back to the list of products which is my desired result. However, I need to know that I am coming from there in the list of products so I can add that product to the shopping cart that is being built for the delivery order.

I am really new in using fragments, but I can pass arguments just fine. What I am struggling is to control the navigation of the fragments through the FragmentActivity that controls the fragments. Also, I am struggling to keep the states of the fragments (remembering user input). At last, I need to go back to the list of products with a result of that item that was being constructed so I can add it to the shopping cart.

Am I going to the right direction? How can I implement these features(navigation, fragment state, returning to previous activity with some data since I just use finish()), Many thanks guys!

Alexios Karapetsas · Accepted Answer · 2015-07-29T19:57:46.150

2

You can navigate between the fragments just by adding them into the back stack like following:

// Works with either the framework FragmentManager or the
// support package FragmentManager (getSupportFragmentManager).
getSupportFragmentManager().beginTransaction()
                           .add(detailFragment, "detail")
                           // Add this transaction to the back stack
                           .addToBackStack()
                           .commit();

That way, when you will click the back button, it wont load the previous activity from the stack but the previous fragment that has been added in the backstack. You can find more details here: http://developer.android.com/training/implementing-navigation/temporal.html

Use the onSaveInstanceState(Bundle savedInstanceState) and the onActivityCreated(Bundle savedInstanceState) on every fragment that you want to save and retrieve data. And then do the following:

public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    if (savedInstanceState != null) {
        //Restore the fragment's state here
        String yourString  = savedInstanceState.getString("key");
    }
}

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
    //save whatever you want into the bundle
    savedInstanceState.putString("key", "your_value");
    // Always call the superclass so it can save the view hierarchy state
    super.onSaveInstanceState(savedInstanceState);
}

You can save whatever you want into the Bundle. From Strings to Parcelables and Serializables. More info here: http://developer.android.com/reference/android/os/Bundle.html

edited Jul 29 '15 at 19:57

answered Jul 29 '15 at 17:04

Alexios Karapetsas

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That might solve one problem but then how will I be back to the list of products since I can´t just use finish() in the the last fragment! – Gustavo Baiocchi Costa Jul 29 '15 at 17:10
@GustavoBaiocchiCosta You can save the items into a database, or in a singleton and retrieve them from any fragment or class you want. This is a code design issue and it's up to you. – Alexios Karapetsas Jul 29 '15 at 17:14
It worked for me, i managed to navigate through the fragments, will try to create a sqlite database and the finish() at the last fragment did take me where I wanted to go! Thanks mate! Accepted yr answer! – Gustavo Baiocchi Costa Jul 29 '15 at 17:20
The problem is that when I go back to the fragment the user selections are gone, the states of the fragments aren´t being recorded or remembered.... how can I do that? – Gustavo Baiocchi Costa Jul 29 '15 at 17:40
That's easy. Look the accepted answer here: http://stackoverflow.com/questions/15313598/once-for-all-how-to-correctly-save-instance-state-of-fragments-in-back-stack – Alexios Karapetsas Jul 29 '15 at 19:01
@GustavoBaiocchiCosta And by the way, if my answer has helped you solved your problem you can accept it. – Alexios Karapetsas Jul 29 '15 at 19:02
Trying to implement that savedinstance, but I dk how to do it... gotta save some stuff somehow – Gustavo Baiocchi Costa Jul 29 '15 at 19:48
If it solves my problem I will definitely accept yr answer, otherwise I will wait for a more complete answer tks – Gustavo Baiocchi Costa Jul 29 '15 at 19:54
@GustavoBaiocchiCosta Did you try the updated answer? – Alexios Karapetsas Jul 29 '15 at 20:24
Not yet Alexios, it does not restore the selection – Gustavo Baiocchi Costa Jul 30 '15 at 13:54
@GustavoBaiocchiCosta what's the problem? what do you see in logs? – Alexios Karapetsas Jul 30 '15 at 14:02
I get a null savedInstanceState alexios – Gustavo Baiocchi Costa Jul 30 '15 at 16:26
I have been reading and it has been said that the onSavedInstanceState is only called when the Activity is being destroyed, which is not my case, I only change the fragment layout, not the host FragmentActivity! – Gustavo Baiocchi Costa Jul 30 '15 at 16:39
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/84722/discussion-between-gustavo-baiocchi-costa-and-alexios-karapetsas). – Gustavo Baiocchi Costa Jul 30 '15 at 16:46
I had to save the data onPause and onDestroy, then on createView i just check if the data is null or not, if not null, then I can restore the views state... Since you helped me a lot I am marking your answer as accepted, thank you! – Gustavo Baiocchi Costa Jul 30 '15 at 20:21

Fragment Management and Navigation (Delivery App)

1 Answers1