Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

New navigation component from arch with nested navigation graph

I have one case and wish to implement it by arch navigation component. For example I have 2 Nav Graphs (main and nested). Can I call main graph from nested and how? enter image description here

like image 276
Serhii Pylypchuk Avatar asked Jun 06 '18 22:06

Serhii Pylypchuk


People also ask

How do you enable your project to use navigation components?

In the Project window, right-click on the res directory and select New > Android Resource File. The New Resource File dialog appears. Type a name in the File name field, such as "nav_graph". Select Navigation from the Resource type drop-down list, and then click OK.

What is popUpToInclusive?

When navigating back to destination A, we also popUpTo A, which means that we remove B and C from the stack while navigating. With app:popUpToInclusive="true" , we also pop that first A off of the stack, effectively clearing it.

What is NavGraph?

NavGraph is a collection of NavDestination nodes fetchable by ID. A NavGraph serves as a 'virtual' destination: while the NavGraph itself will not appear on the back stack, navigating to the NavGraph will cause the starting destination to be added to the back stack.


2 Answers

The point is to get the right NavController to navigate in the right graph. Let's take this scenario as an example:

MainActivity |- MainNavHost    |- NavBarFragment    |  |- NestedNavHost    |  |  |-NestedContentFragment1    |  |  |-NestedContentFragment2    |  |    |  |- BottomNavigationView    |    |- LoginFragment 

The main graph and the nested graph are in separate xml files: this is required, as far as I understood, because the navigations target different layout areas, so they require two different NavHosts. Each Navhost will need to reference its graph by id, which requires them to be in different resource files.

The point is that to navigate in a specific graph, we must get a reference to the right graph's owner: to do this, when calling Navigation.findNavController(view), the view argument is crucial.

Docs say that

NavHostFragments register their navigation controller at the root of their view subtree such that any descendant can obtain the controller instance through the Navigation helper class's methods

So for example, if inside NavBarFragment we write

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {     navController = Navigation.findNavController(view) } 

here view is a parent of the NestedNavHost (that is the nested NavHostFragment), not a descendant, meaning that findNavController will search upstream in the tree and will return the MainNavHost's NavController.

If instead we write

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {     val nestedNavHostFragment = childFragmentManager.findFragmentById(R.id.nestedNavHostFragment) as? NavHostFragment     navController = nestedNavHostFragment?.navController } 

where nestedNavHostFragment is the id of the FragmentContainerView in the layout, we get a reference to the correct NestedNavHost. Note the use of childFragmentManager, not parentFragmentManager.

In case you're still using the deprecated xml <fragment> tag, you can write

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {     val fragmentContainer = view.findViewById<View>(R.id.nestedNavHostFragment)     navController = Navigation.findNavController(fragmentContainer) } 

where nestedNavHostFragment is the id of the <fragment> tag. We get a reference to the correct NestedNavHost now, because the view we pass to findNavController belongs to the NestedNavHost's subtree.

Similarly, if you need to get a reference to the main NavController from inside a NestedContentFragment, here's what we can do:

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {     // we can get the innermost NavController using this view,     // because we are inside its subtree:     nestedNavController = Navigation.findNavController(view)      // we can find the outer NavController passing the owning Activity     // and the id of a view associated to that NavController,     // for example the NavHostFragment id:     mainNavController = Navigation.findNavController(activity!!, R.id.mainNavHostFragment) } 
like image 192
devrocca Avatar answered Sep 21 '22 22:09

devrocca


Actually you could use Global actions to navigate from a nested nav graph destination to a main nav graph destination.

Create a global action from nested nav graph to desired destination in main nav graph (highlighted in the image below)

example:

nav graph

<navigation android:id="@+id/main_nav_graph"      ... >      <fragment android:id="@+id/fragStart" .../>      <fragment .../>      <fragment .../>       <navigation  android:id="@+id/nested_nav_graph">            ...       <!-- Global Action -->      <action          android:id="@+id/action_global_start"          app:destination="@id/fragStart" />      </navigation>  </navigation> 

To navigate to main graph destination use

findNavController().navigate(R.id.action_global_start) 
like image 42
user158 Avatar answered Sep 20 '22 22:09

user158