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[Navigation] Return early from NavigatorProvider#addNavigator if possible #176

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[Navigation] Return early from NavigatorProvider#addNavigator if possible #176

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Return early from NavigatorProvider#addNavigator if previous & naviga… 
…tor are equal

We want to return early from `addNavigator` if the previous and to-be-added navigator are equal. This allows calling `addNavigator` as a side effect of every composition without having to worry about the Navigator being replaced every time.

Test: Added addExistingNavigatorDoesntReplace and addWithSameNameButUnequalNavigatorDoesReplace in NavigatorProviderTest.kt

Fixes: b/187443146
Change-Id: Id09b7e3306c49f261b80c724d36c614671f5a7ac
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@jossiwolf
jossiwolf committed May 7, 2021
commit ba934c563f6e50f20d147be86bba254285c524da
3 changes: 3 additions & 0 deletions navigation/navigation-common/src/main/java/androidx/navigation/NavigatorProvider.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -103,6 +103,9 @@ public open class NavigatorProvider {
): Navigator<out NavDestination>? {
require(validateName(name)) { "navigator name cannot be an empty string" }
val previousNavigator = _navigators[name]
if (previousNavigator == navigator) {
return navigator
}
check(previousNavigator?.isAttached != true) {
"Navigator $navigator is replacing an already attached $previousNavigator"
}
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45 changes: 45 additions & 0 deletions navigation/navigation-common/src/test/java/androidx/navigation/NavigatorProviderTest.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@
package androidx.navigation

import android.os.Bundle
import androidx.navigation.testing.TestNavigatorState
import com.google.common.truth.Truth.assertThat
import com.google.common.truth.Truth.assertWithMessage
import org.junit.Assert.fail
Expand Down Expand Up @@ -100,6 +101,50 @@ class NavigatorProviderTest {
.isEqualTo(navigator)
}

@Test
fun addExistingNavigatorDoesntReplace() {
val navigatorState = TestNavigatorState()
val provider = NavigatorProvider()
val navigator = EmptyNavigator()

provider.addNavigator(navigator)
assertThat(provider.getNavigator<EmptyNavigator>(EmptyNavigator.NAME))
.isEqualTo(navigator)

navigator.onAttach(navigatorState)
assertWithMessage("Navigator should be attached")
.that(provider.getNavigator<EmptyNavigator>(EmptyNavigator.NAME).isAttached)
.isTrue()

// addNavigator should throw when trying to replace an existing, attached navigator, but
// we should have returned before that
try {
provider.addNavigator(navigator)
} catch (navigatorAlreadyAttached: IllegalStateException) {
fail(
"addNavigator with an existing navigator should return early and not " +
"attempt to replace"
)
}
}

@Test
fun addWithSameNameButUnequalNavigatorDoesReplace() {
val provider = NavigatorProvider()
val navigatorA = EmptyNavigator()
val navigatorB = EmptyNavigator()

assertThat(navigatorA).isNotEqualTo(navigatorB)

provider.addNavigator(navigatorA)
assertThat(provider.getNavigator<EmptyNavigator>(EmptyNavigator.NAME))
.isEqualTo(navigatorA)

provider.addNavigator(navigatorB)
assertThat(provider.getNavigator<EmptyNavigator>(EmptyNavigator.NAME))
.isEqualTo(navigatorB)
}

private val provider = NavigatorProvider()

@Test
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