coco
57 lines
2.0 KiB
Markdown
57 lines
2.0 KiB
Markdown
# Stack API
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### SnapshotStateStack
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Voyager is backed by a [SnapshotStateStack](https://github.com/adrielcafe/voyager/blob/main/voyager-core/src/main/java/cafe/adriel/voyager/core/stack/SnapshotStateStack.kt):
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* Implementation of [Stack](https://github.com/adrielcafe/voyager/blob/main/voyager-core/src/main/java/cafe/adriel/voyager/core/stack/Stack.kt) that can be observed and snapshot
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* Internally uses a [SnapshotStateList](https://developer.android.com/reference/kotlin/androidx/compose/runtime/snapshots/SnapshotStateList)
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* State-aware: content change triggers a [recomposition](https://developer.android.com/jetpack/compose/mental-model#recomposition)
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You will use it to navigate forward (`push`, `replace`, `replaceAll`) and backwards (`pop`, `popAll`, `popUntil`), but the `SnapshotStateStack` can also be used as a regular collection outside the `Navigator`.
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```kotlin
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val stack = mutableStateStackOf("🍇", "🍉", "🍌", "🍐", "🥝", "🍋")
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// 🍇, 🍉, 🍌, 🍐, 🥝, 🍋
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stack.lastItemOrNull
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// 🍋
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stack.push("🍍")
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// 🍇, 🍉, 🍌, 🍐, 🥝, 🍋, 🍍
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stack.pop()
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// 🍇, 🍉, 🍌, 🍐, 🥝, 🍋
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stack.popUntil { it == "🍐" }
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// 🍇, 🍉, 🍌, 🍐
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stack.replace("🍓")
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// 🍇, 🍉, 🍌, 🍓
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stack.replaceAll("🍒")
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// 🍒
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```
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You can also create a `SnapshotStateStack` through `rememberStateStack()`, it will [restore the values](state-restoration.md) after Activity recreation.
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### **Events**
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Whenever the content changes, the `SnapshotStateStack` will emit a `StackEvent`. Use the `stack.lastEvent` to get the most recent one.
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The available events are:
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* `Push`: whenever `push` is called
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* `Replace`: whenever `replace` and `replaceAll` are called
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* `Pop`: whenever `pop` and `popAll` are called
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* `Idle`: default event
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This is very useful for deciding which [transition](transitions-api) to make.
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### Sample
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!!! info
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Source code [here](https://github.com/adrielcafe/voyager/tree/main/samples/android/src/main/java/cafe/adriel/voyager/sample/stateStack).
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