Let us consider the situation when you have ContentView
and DestinationView
. Both of them depend on some shared data, that typically lies inside the @ObservedObject var viewModel
, that you pass from parent to child either via @EnvironmentObject
or directly inside init()
.
The DestinationView
in this case wants to enrich the viewModel by fetching some additional content inside .onAppear
.
In this case, when using NavigationLink
you might encounter the situation when the DestinationView
gets into an update loop when you fetching content, as it also updates the parent view and the whole structure is redrawn.
When using the List
you explicitly set the row's ids and thus view is not changed, but if the NavigationLink
is not in the list, it would update the whole view, resetting its state, and hiding the DestinationView
.
The question is: how to make NavigationLink
update/redraw only when needed?
In SwiftUI the update mechanism compares View structs to find out whether they need to be updated, or not. I've tried many options, like making ViewModel
Hashable
,Equatable
, andIdentifiable
, forcing it to only update when needed, but neither worked.The only working solution, in this case, is making a
NavigationLink
wrapper, providing it withid
for equality checks and using it instead.Then in
ContentView
use it with.equatable()
Helpful tip:
If your
ContentView
also does some updates that would impact the DestinationView it's suitable to use LazyView to prevent Destination from re-initializing before it's even on the screen.P.S: Apple seems to have fixed this issue in iOS14, so this is only iOS13 related issue.