Managing Android Fragment Backstack Through Tags by Heming Liu Tubi Engineering

However at some point you are likely going to run into a situation that doesn’t quite fit the mold of a an application with a simple back stack. Note that you must always use getChildFragmentManager when interacting with nested fragments instead of using getSupportFragmentManager. Read this stackoverflow post for an explanation of the difference between the two.

fragment backstack

The user can tap on an item in RosterListFragment to bring it up in DisplayFragment, and the user can click an “edit” toolbar button to bring it up in EditFragment. When an activity goes into the background, the activity is placed in the back stack. This allows the activity to be resumed when the user presses the Back button. To update the drawer when the back stack changes, make a method that accepts in a Fragment and compares the class names. Also add an OnBackStackChangedListener and have it call your update method if there is a valid Fragment. The problem is, when I launch A and then B, then press ‘back’, B is removed and A is resumed.

Organizing your Code

We use getFragmentTag() to get the unique tag per fragment instance for fragment transaction. In our library, to make it easier to look up and reference, we use the same tag for both the fragment instance and Automate Software Testing and Delivery transaction. Note that each tag is unique for each fragment instance, so that we can manipulate multiple instances of the same class. Google recommends using FragmentTransaction to manipulate fragments.

One textview and two buttons are there in the above layout file. In onCreateView() method, compiler will Python-Crash-Course Python101 inflate the fragment_fragment_one.xml file. Thus, it will get the view of fragment_fragment_one.xmlfile.

We want this library to help ease the pain of dealing with the Fragment backstack for fellow Android developers. We hope you’ll give it a shot and would love to get feedback on it. I am having troules understanding how fragments work in saving and restoring data and other things. With the above, making an app that has a navigation pattern similar to Instagram becomes easy. Now, whenever the back stack changes, the title and checked position will reflect the visible Fragment. But I want to resume A and destroy all fragments on top of it .

When we load a new Fragment instance, based on the type of new Fragment instance, we save the previous Fragment instance tag to new Fragment instance. If a Fragment instance is marked as skipOnPop, it will maintain a tag pointing to the last Fragment instance that should not be skipped. You are welcome to use hide() and show() on a FragmentTransaction to hide and show fragments. Hide() does not remove or destroy the fragment; it simply removes its views from the view hierarchy. Now, suppose that the business rule is that when we save our changes in EditFragment, we are to return to the RosterListFragment.

Now let us create practical examples with android studio to see how the theory of fragment actually works in android app. After this much information, you have enough basic idea about the importance of the fragment in android app development. This is where fragments help us to create such type of designs without handling the complex view hierarchy. When you Google Apps Script Wikipedia add a fragment as a part of your activity layout, it lives in a ViewGroup inside the activity’s view hierarchy and the fragment defines its own view layout. Android also provides the feature to add the fragment to the backstack similar to that the backstack of activity. Every fragment’s lifecycle is directly affected by it’s parent activity’s lifecycle.

Show me the code

To place a fragment into the back stack, you need to explicitly call the addToBackStack() method during a fragment transaction. Since you want only one back stack entry per Fragment, make the back state name the Fragment’s class name (via getClass().getName()). Then when replacing a Fragment, use the popBackStackImmediate() method.

fragment backstack

When the user clicks on any article from the list, we will open another activity with second fragment which will show up the whole article. Now for the same application, consider the screen of mobile device. In the larger screen of the tablet, there is much more space to combine and interchange the UI components effectively. We can also pass the name of the transaction and upto that transaction, all other transactions will be removed. A sample Android application to demonstrate how to build screens as fully independent modules. In addition to the fragment system automatically handling BACK, you might have a need to go back programmatically, and sometimes you need to go back multiple levels.

It fully supports iOS tabs style navigation, which means it keeps and maintains multiple child Fragment backstacks. The method showFragment() is the one we use to show a Fragment on the screen; we invoke it every time we need to change the visible Fragment. If we want to save the current transaction being able to come back to the current Fragment we pass true as addToStack value, otherwise we pass false. Reading the documentation, there is a way to pop the back stack based on either the transaction name or the id provided by commit. Using the name may be easier since it shouldn’t require keeping track of a number that may change and reinforces the “unique back stack entry” logic. Inevitably in certain cases you will want to embed a fragment within another fragment.

Remove one transaction from backstack:

OnCreateView() is called by Android once the Fragment should inflate a view. OnCreate() is called to do initial creation of the fragment. View state management logic such as visibility or error handling. You can find the code here (artificial-back-stack branch). And allow him to rejoin the flow at the last point he left (and don’t lose a user because of a long sign-up process). Welcome to Android Fragments Backstack lifecycle tutorial for beginners.

Your Activity for Fragment operation has to extend from FoActivity. FileNotFoundException (java.io)Thrown when a file specified by a program cannot be found. EOFException (java.io)Thrown when a program encounters the end of a file or stream during an input operation. The Lists tab is delved into further, by pushing the detail AdoptDoggoFragment unto its stack.

Going back partway through the stack isn’t particularly easy with this approach. For more details about this pattern, check out our detailed Creating Custom Listeners guide. This pattern makes passing arguments to fragments for initialization fairly straightforward.

  • When I opened the main activity first, the first fragment is running inside the frame layout.
  • The FragmentManager class and the FragmentTransaction class allow you to add, remove and replace fragments in the layout of your activity at runtime.
  • First activity will hold the first fragments with the lists of the articles.
  • The other option is to pass in zero, which will pop everything up to the specified state.
  • In my example this would leave the current tab on the backstack, so hitting back after navigating to a tab would bring you back to the previous tab.

Thus, you can see that we have learn how to control the click event and to change the value of textview from the JAVA file of the fragment. When the user clicks the button, we change the value of the textview. Click event of both button will fill different text in the textview. In this example, I will show you how to control the UI widgets like textview, button, Imageview etc. in the fragment’s java class.

And while in this case we only need to skip one Fragment instance , what if there are multiple fragments that need to be skipped? We definitely don’t want to call popBackStack() multiple times, all at once. So it would be really nice if this can be handled automatically. All i want to have is an activity with 2 fragments frag1 and frag2, each with a button , and edittext and textview, sending and recieving data while saving their state. You may also opt to perform these operations synchronously or asynchronously, or add a tag to them. For these reasons, the FragmentManager should not be the API surface you use to implement navigation in your app; it needs an abstraction that delegates to it.

One solution: manage the backstack yourself

First activity will hold the first fragments with the lists of the articles. For example, suppose you have an app like the ToDo app from Exploring Android. We have a list of to-do items , a screen to display details of a to-do item , and a screen to edit details of a to-do item .

While textview says that it is placed in the layout of activity so that we can differentiate the area of activity with the area of fragment. Inside this fragment, we will add one textview and two buttons. This method will use FragmentManager and FragmentTransaction class to create a fragment. If it’s value is true then compiler will add this fragment to the backstack. On the click event of both textviews, we will make different fragments. Let us create two fragments example in android studio to see the practical execution of fragments.

The Nav and Lists tab are then alternated between to show that their independent stack states are preserved. The conditional was changed a bit since selecting the same fragment while it was visible also caused duplicate entries. And when I press the ‘back’ button, B is destroyed and C is resumed. When I used this approach, I ran into a few quirks that I didn’t like. This is true, and you shouldn’t be afraid to manage the back stack yourself if the framework simply isn’t going to work in your scenario.