Pick one: Setting your nav graph

tl;dr Only add your nav graph one place. Want to know why, read on.

I was learning how to use navigation components and I did what many of us do: read a bunch of blog posts to piece together how to do what I wanted to accomplish. You all have created so many great resources on how to use the latest libraries. I had navigation set up for this feature in no time.

It wasn’t long after that I started to notice some odd behavior. When rotating the device, I would always end on my start destination no matter where I was in the graph. For example, say I had a start destination fragment of a list and a detail fragment that I navigated to when you click a list item. After navigating to the detail fragment, then rotate the device, I would be back on the start destination list.

I dug into the source code (which I later discovered I misunderstood). It suggested to me that I should only set the graph in the activity if it was the first time the activity was opened. I added a check for savedInstanceState, and it seemed to solved the problem. I soon found out I was mistaken.

// DON'T DO THIS
if (savedInstanceState == null) {
    findNavController(R.id.navHostFragment)
        .setGraph(R.navigation.nav_graph)
}
// DON'T DO THIS

I got into a conversation about another problem I was trying to solve, and this came up. It was there I learned this gotcha: you shouldn’t set your nav graph in both your layout xml file and the activity code. This essentially sets the graph twice and resets everything.

You can either set it in your xml using app:navGraph:

<fragment
    android:id="@+id/navHostFragment"
    android:name="androidx.navigation.fragment.NavHostFragment"
    app:defaultNavHost="true"
    app:navGraph="@navigation/new_events_nav_graph" />

OR you can set it in your activity using setGraph:

findNavController(R.id.navHostFragment)
    .setGraph(R.navigation.nav_graph)

Moral of the story: Pick on place to set your graph.

Huge thanks to Ian Lake for pointing this out to me.

04/06/2020

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Pick one: Setting your nav graph