Android fragments inside fragments

RecyclerView inside Fragment with Android Studio

In developing an Android application, there are two approaches. Native and Hybrid. Native applications developed for a specific platform, meanwhile hybrid applications developed for multiple platforms on a single base. In native, Android applications are written in Java-based, and iOS are written in Swift. My Software Development Project was requested by our client to use Native apps to develop our project. So, we use both Kotlin and Swift language for our project.

“The secret of getting ahead is getting started” — Mark Twain

My job during this development is developing the Android one. We use Android Studio as our IDE. It is an official IDE by Google for developing Android applications. Well, this is my last article related to my Software Development Project course. This time, I want to share my experience using Android Studio and Kotlin for the first time, especially in making a Recycler View, and to be more complicated, it is also inside a Fragment.

First thing first, please make sure you’ve already prepared this:

Understand the Concept

Before we start, you need to know what is exactly RecyclerView, CardView, and Fragment. For a more complete explanation, please see Android Developers.

RecyclerView

Sometimes in an application, we want to display a large set of data. Here we certainly need a view that can handle it. Several different components work together to display the data. All container for the User Interface is a RecyclerView object that you add to the layout. LayoutManager such as LinearLayoutManager or GridLayourManager could be your layout manager to fill the RecyclerView.

CardView

Package view of Material Design which commonly used for wrapping data, package data in several views. This view has a drop shadow and a corner radius. This is a subclass of FrameLayout.

Fragment

A fragment represents a portion of User Interface in a FragmentActivity. Multiple fragments could be combined in a single activity and reuse a fragment in multiple activities. We implement this fragment because at the end we want to make this recycler view page could be slide to another page. Here’s the illustration of it.

Let’s jump to the implementation

Here I want to make a RecyclerView consist of CardView, which is inside a Fragment.

Prepare the Android Studio

1. Create a New Project on Android Studio. Choose Empty Activity.

2. Add your file name, then click Finish

Add the Dependencies

Adding the dependencies for RecyclerView and CardView on your build.gradle (app stage).

Then do the Sync Project with Gradle Files

Add RecyclerView to layout

Next, add RecyclerView code on your res/layout XML file. Because I want to make it inside a Fragment, which could work with FrameLayout. So, the Root Element is FrameLayout.

1. Right-click the layout folder and go to New > Layout resource file
2. Add your file name
3. Select the Root Element with FrameLayout, then click OK

Create the layout with ConstraintLayout and RecyclerView.

Here’s the layout.

Create a CardView layout

Same as adding RecyclerView to layout, but the Root Element is CardView or androidx.cardview.widget.CardView.

I divided the row inside the CardView with LinearLayout, which is inside a RelativeLayout to makes them responsive. To insert the font and strings to the XML, don’t forget to add the resources first on the values folder. You can see the tutorial on my article about implement design guidelines here.

Here’s the layout.

Create an Adapter for the RecyclerView

On making RecylerView, there is must be an adapter to connect the RecyclerView with the CardView. The views in the list are represented by view holder objects. By extending RecyclerView.ViewHolder, these objects are instances of a class you defined. Each view holder is in charge of showing a single item with a view. This shows a list of questions, each view holder might represent a single question. The RecyclerView creates the same number of view holders as are expected to show the on-screen portion of the dynamic content. As the user scrolls through the list, the RecyclerView takes the off-screen views and rebinds them to the data which is scrolling onto the screen. The view holder objects are managed by an adapter, by extending RecyclerView.Adapter. This adapter created view holders as needed and also binds it to the data.

Here’s my model are a component that will be on the card later, such a code, category, and content. This fragment class will call the layout we’ve made before.

In the upcoming implementation, the data for the components are automatically fetched from the API. This code only shows if the data are input manually from the array.

For the simple implementation, create ViewHolder as an inner class on the RecyclerAdapter class.

DetailPertanyaan is an activity if the card has been clicked. For the supporting method in RecyclerAdapter class, add this code below the ViewHolder class.

onCreateViewHolder() needs to construct a RecyclerView.ViewHolder and set the view to display its contents. It would set the view by inflating the CardView layout.

onBindViewHolder() uses the view holder’s position to determine what the contents should be.

Set the Adapter to RecyclerView on Fragment class

This class will call the layout that consists of the RecyclerView and connect the adapter with the RecyclerView.

onViewCreated() will set the RecyclerAdapter to the RecyclerView layout.

Last but not least, don’t forget to Run your ‘app’ to see the result!

I will not explain more about the further Fragment implementation, you can use TabLayout as the sections pager adapter and ViewPager to make the page could be slide to the next fragment. This tutorial I made only for one fragment. There are so many inspirations and tutorials out there to explore more about this layout. This card also could be clicked and go to another activity, and the tutorials are also available on the internet. Hehe

Closing Statement

On developing my project with Android Kotlin, there are so many lessons that I learned. This is not the only task that I do, there is also another task. I learned a lot about this new framework, I use Android Studio and Kotlin for the first time. I learned it from the basics. Before we start the project, our client gave us a free course in Udemy on Android Fundamentals. You also can learn it here.

When I first succeed in making the sign-in layout, I am feeling very very joyful! My layout for the sign-in page was made on the Design option. It is very easy because you will feel like design a mockup, just drag and choose the details on the Attributes. As time goes by, I easily understand how to make the UI for Android and made the layout on the Text option, so I literally code the layout. I also learn how to make a SwipeRefreshLayout, Onboarding pages, and account page. There are also different obstacles in every task I did. I can increase my ability in every task I did on this project. So, if you want to learn about the native mobile application you could use Kotlin as your programming language and Android Studio for the IDE.

With this article, I officially finished my individual review writings on what has been learned and implemented in developing a project. Thank you for reading all my individual review, I’ll be glad that you read this last sentence. Especially, thank you Mr. Mishbah for grading all these articles 😀

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Android Fragments Common Queries & Common Mistakes

Fragment class in Android is used to build dynamic User Interfaces. Fragment should be used within the Activity. A greatest advantage of fragments is that it simplifies the task of creating UI for multiple screen sizes. A activity can contain any number of fragments.

Now this meaning of fragment sounds good and easy, right? But there is lot more involved, this article covers main needs and common mistakes while using Fragments.

I am assuming you are having basic knowledge of Fragment and Fragment lifecycle callbacks also I am assuming you know how implement communication between two fragments this article goes beyond that

So here are a few obstacles related to fragments some of you must have faced already, some of you might face later.

• FragmentManager: getSupportFragmentManager and getChildFragmentManager. Which one to use when and avoid memory leaks while using them.
• Callback from DialogFragment, ChildFragment, BottomSheetFragment to parent fragment.
• Fragments when using ViewPager and when to use FragmentStateAdapter vs FragmentPagerAdapter.
• When to use FragmentTransaction add vs replace ?
• Fragment receivers, broadcasts and memory leaks.
• Fragment BottomBarNavigation and drawer. How to handle these?
• commit() and commitAllowingStateLoss()
• Fragment option menus.
• Fragment getActivity(), getView() and NullPointers Exceptions.
• onActivityResult with nested fragments.
• Fragment and Bundle.
• Back Navigation.

Whoa . see its a big list, reply in comment if anyone wish to add something more to the list.

getSupportFragmentManager and getChildFragmentManager

FragmentManager is class provided by the framework which is used to create transactions for adding, removing or replacing fragments.

• getSupportFragmentManager is associated with Activity consider it as a FragmentManager for your Activity .

So whenever you are using ViewPager, BottomSheetFragment and DialogFragment in an Activity you will use getSupportFragmentManager

• getChildFragmentManager is associated with fragment.

Whenever you are ViewPager inside Fragment you will use getChildFragmentManager

Here is official link for this for better understanding.

Now coming to common mistakes people do when they are using ViewPager inside a Fragment they pass getSupportFragmentManager which is fragment manager for Activity and it causes issues as such memory leaks, ViewPager not updated properly sometimes etc.

Most important issue caused by using getSupportFragmentManager in Fragment is memory leak, let me tell you how? Your Fragment has stack of fragments which is used by ViewPager or any other thing and all these fragments stack is in activity since you used getSupportFragmentManager , now if close your Parent fragment it will be closed but it will not be destroyed because all child Fragments are in activity and they are still in memory which does not allow to destroy Parent Fragment hence causing leak. It will not just leak parent fragment but also leak all child fragments since none of them can be cleared from heap memory. So never try to use getSupportFragmentManager in a Fragment

Callback from DialogFragment, ChildFragment, BottomSheetFragment to parent fragment

This is very common issue people face when they use BottomSheetFragment or DialogFragment or ChildFragment.

Add a child fragment

Another example bottomSheetFragment

Now suppose you want callback from these child fragments to parent fragments . Most of people create connection between two fragments using activity, few people pass interface listeners as a parameter to fragment which really a bad practice and one should avoid this. Best way calling getParentFragment() from your child fragment to create a call back this is very simple way consider example below.

then setting callback to parent fragment add following code in child fragment.

thats it you can give a callback to your parent fragment now easily.

Using same way you can create a callback from child fragment inside ViewPager to parent fragment who is holding ViewPager.

Fragments when using ViewPager and adapters FragmentStateAdapter and FragmentPagerAdapter which one one to use when

FragmentPagerAdapter stores the whole fragment in memory, and could increase a memory overhead if a large amount of fragments are used in ViewPager . FragmentStatePagerAdapter only stores the savedInstanceState of fragments, and destroys all the fragments when they lose focus.

So when your is going to have many Fragments use FragmentStateAdapter if ViewPager is going to have less than three fragments use FragmentPagerAdapter.

Commonly faced issues

Update ViewPager not working:

People always come across the issue remember ViewPager fragments are managed by FragmentManager either from Fragment or Activity and this FragmentManager holds instance of all ViewPager Fragments.

So when people say ViewPager is not refreshed it’s nothing but old instances of fragments are still being hold by FragmentManager. So you need to find out why FragmentManger is holding instance of Fragments is there any leak or not ideally to refresh ViewPager following code works if it is not you are doing something wrong

Access current Fragment from ViewPager:

This is also very common issue we come across. For this people either create array list of fragments inside adapter or try to access fragment using some tags according to me both methods are not reliable. FragmentStateAdapter and FragmentPagerAdapter both provides method setPrimaryItem this can be used to set current fragment as below.

I am leaving a Github link below to this simple ViewPager project so that everyone can understand better.

amodkanthe/ViewPagerTest

Contribute to amodkanthe/ViewPagerTest development by creating an account on GitHub.

FragmentTransaction add vs replace

In our Activity we have a container and inside this container we display our Fragments

add will simply add fragment to container suppose you add FragmentA and FragmentB to container. Container will have FragmentA and FragmentB both and suppose if container is FrameLayout fragments are added one above the other. replace will simply replace a fragment on top of container so if I call create FragmentC now and call replace FragmentB which was on top will removed from container unless you are not calling addToBackStack and now FragmentC will be on top.

So which one to use when. replace removes the existing fragment and adds a new fragment . This means when you press back button the fragment that got replaced will be created with its onCreateView being invoked. Whereas add retains the existing fragments and adds a new fragment that means existing fragment will be active and they wont be in ‘paused’ state hence when a back button is pressed onCreateView is not called for the existing fragment(the fragment which was there before new fragment was added). In terms of fragment’s life cycle events onPause, onResume, onCreateView and other life cycle events will be invoked in case of replace but they wont be invoked in case of add .

Use replace fragment if don’t need to revisit current fragment and current fragment is not require anymore. Also if your app has memory constraints use replace instead of add.

Fragment receivers, broadcasts and memory leaks

Mistakes people commonly do when using receivers inside a fragment forgot to unregister receiver in onPause or OnDestroy. If you are registering fragment to listen to receiver inside onCreate or OnResume you will have to unregister it inside onPause or onDestroy otherwise it will cause memory leak

Also if have multiple fragments listening to same broadcast receiver make sure you register in onResume and unregister in onPause. Because if you use onCreate and onDestroy for register and unregister other fragments will not receive the broadcast as this fragment is not destroyed

Fragment BottomBarNavigation and drawer how to handle these

When we are using BottomBarNavigation and NavigationDrawer people face issues like fragments recreated, same fragment is added multiple times etc.

So in such case you can use fragment transaction show and hide instead of add or replace.

There is also one beautiful library which take care of navigations and avoid recreation of fragments called FragNav below is link to it

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