IssueTracker

Partly, this is my fault -- val is not that useful in the @Model context, since @Model relies on mutability. I am used to thinking in terms of immutable viewstates and screwed this up.

However, it probably should not crash this way. Either it should work (with a never-changing value) or it should fail with a "are you *really* sure you want this here?" sort of error.

I'd like to add that declaring `canProceed` as a `var` won't crash the app.
The extension function is avoidable by just having the `get()`-getter function inside the class itself. That also avoids the crash.

Try,

@Model
data class AgreementViewState(var terms: Boolean, var privacy: Boolean) {
    val canProceed get() = terms && privacy
}

(note the addtion of get()) which seems to be what you intended. `val canProceed = terms && privacy` is not a derived property, rather, it is an initialized property.

Yes, that echoes comment #3. It too works, akin to fun canProceed(), an external extension function, and a var. So, in terms of having working approaches, I'm good.

I'll still argue that the initialized val shouldn't blow up the way that it does, though.

Does Model support val properties in the primary constructor? What if I want to update (rebind) view with the NEW data from the API for e.g. and not necessarily update var fields in the existing @Model data, is that supported?

It is generally advised in the Kotlin community to "limit mutability" and use 'val' as much as possible (book Effective Kotlin by Marcin Moskala), while here you advise all @Model data to use var fields?

Epoxy library works great with immutable models, and always properly rebinds existing views based on new immutable Model objects you pass into it.

Project: platform/frameworks/support
Branch: androidx-master-dev

commit fcf76b3241844f18106d6e850004952046d4bfb6
Author: Leland Richardson <lelandr@google.com>
Date:   Wed May 13 16:58:59 2020

    Deprecate @Model
   
    Relnote: “
    @Model annotation is now deprecated. Use state and mutableStateOf as alternatives. This deprecation decision was reached after much careful discussion.
   
    Justification
    =============
   
    Rationale includes but is not limited to:
    - Reduces API surface area and concepts we need to teach
    - More closely aligns with other comparable toolkits (Swift UI, React, Flutter)
    - Reversible decision. We can always bring @Model back later.
    - Removes corner-case usage and difficult to answer questions about configuring @Model as things we need to handle
      - @Model data classes, equals, hashcode, etc.
      - How do I have some properties “observed” and others not?
      - How do I specify structural vs. referential equality to be used in observation?
    - Reduces “magic” in the system. Would reduce the likelihood of someone assuming system was smarter than it is (ie, it knowing how to diff a list)
    - Makes the granularity of observation more intuitive.
    - Improves refactorability from variable -> property on class
    - Potentially opens up possibilities to do hand-crafted State-specific optimizations
    - More closely aligns with the rest of the ecosystem and reduces ambiguity towards immutable or us “embracing mutable state”

   
    Migration Notes
    ===============
   
    Almost all existing usages of @Model are fairly trivially transformed in one of two ways. The example below has a @Model class with two properties just for the sake of example, and has it being used in a composable.
   
    ```
    @Model class Position(
     var x: Int,
     var y: Int
    )
   
    @Composable fun Example() {
     var p = remember { Position(0, 0) }
     PositionChanger(
       position=p,
       onXChange={ p.x = it }
       onYChange={ p.y = it }
     )
    }
    ```
   
    Alternative 1: Use State<OriginalClass> and create copies.
    ----------------------------------------------------------
   
    This approach is made easier with Kotlin’s data classes. Essentially, make all previously `var` properties into `val` properties of a data class, and then use `state` instead of `remember`, and assign the state value to cloned copies of the original using the data class `copy(...)` convenience method.
   
    It’s important to note that this approach only works when the only mutations to that class were done in the same scope that the `State` instance is created. If the class is internally mutating itself outside of the scope of usage, and you are relying on the observation of that, then the next approach is the one you will want to use.
   
    ```
    data class Position(
     val x: Int,
     val y: Int
    )
   
    @Composable fun Example() {
     var p by state { Position(0, 0) }
     PositionChanger(
       position=p,
       onXChange={ p = p.copy(x=it) }
       onYChange={ p = p.copy(y=it) }
     )
    }
    ```
   
    Alternative 2: Use mutableStateOf and property delegates
    --------------------------------------------------------
   
    This approach is made easier with Kotlin’s property delegates and the `mutableStateOf` API which allows you to create MutableState instances outside of composition. Essentially, replace all `var` properties of the original class with `var` properties with `mutableStateOf` as their property delegate. This has the advantage that the usage of the class will not change at all, only the internal implementation of it. The behavior is not completely identical to the original example though, as each property is now observed/subscribed to individually, so the recompositions you see after this refactor could be more narrow (a good thing).
   
    ```
    class Position(x: Int, y: Int) {
     var x by mutableStateOf(x)
     var y by mutableStateOf(y)
    }
   
    // source of Example is identical to original
    @Composable fun Example() {
     var p = remember { Position(0, 0) }
     PositionChanger(
       position=p,
       onXChange={ p.x = it }
       onYChange={ p.y = it }
     )
    }
    ```
    “
   
    Bug: 156546430
    Bug: 152993135
    Bug: 152050010
    Bug: 148866188
    Bug: 148422703
    Bug: 148394427
    Bug: 146362815
    Bug: 146342522
    Bug: 143413369
    Bug: 135715219
    Bug: 126418732
    Bug: 147088098
    Bug: 143263925
    Bug: 139653744
   
    Change-Id: I409e8c158841eae1dd548b33f1ec80bb609cba31

M       compose/compose-compiler-hosted/integration-tests/src/test/java/androidx/compose/plugins/kotlin/frames/FrameDiagnosticTests.kt
M       compose/compose-runtime/api/0.1.0-dev12.txt
M       compose/compose-runtime/api/current.txt
M       compose/compose-runtime/api/public_plus_experimental_0.1.0-dev12.txt
M       compose/compose-runtime/api/public_plus_experimental_current.txt
M       compose/compose-runtime/api/restricted_0.1.0-dev12.txt
M       compose/compose-runtime/api/restricted_current.txt
M       compose/compose-runtime/compose-runtime-benchmark/src/androidTest/java/androidx/compose/benchmark/ComposeBenchmark.kt
M       compose/compose-runtime/compose-runtime-benchmark/src/androidTest/java/androidx/compose/benchmark/SiblingBenchmark.kt
M       compose/compose-runtime/compose-runtime-benchmark/src/androidTest/java/androidx/compose/benchmark/dbmonster/DbMonster.kt
M       compose/compose-runtime/compose-runtime-benchmark/src/androidTest/java/androidx/compose/benchmark/realworld4/RealWorld4_DataModels.kt
M       compose/compose-runtime/samples/src/main/java/androidx/compose/samples/ModelSamples.kt
M       compose/compose-runtime/src/commonMain/kotlin/androidx/compose/FrameManager.kt
M       compose/compose-runtime/src/commonMain/kotlin/androidx/compose/Model.kt
M       compose/compose-runtime/src/commonMain/kotlin/androidx/compose/MutableState.kt
M       compose/compose-runtime/src/commonMain/kotlin/androidx/compose/Observe.kt
M       compose/compose-runtime/src/commonMain/kotlin/androidx/compose/Recompose.kt
M       compose/compose-runtime/src/commonMain/kotlin/androidx/compose/StableMarker.kt
M       ui/integration-tests/benchmark/src/androidTest/java/androidx/ui/benchmark/test/ModelObserverBenchmark.kt
M       ui/integration-tests/benchmark/src/androidTest/java/androidx/ui/benchmark/test/RadioGroupBenchmark.kt
M       ui/integration-tests/demos/src/main/java/androidx/ui/demos/DemoColorPalette.kt
M       ui/integration-tests/src/main/java/androidx/ui/integration/test/foundation/RectsInColumnSharedModelTestCase.kt
M       ui/ui-android-view/integration-tests/android-view-demos/src/main/java/androidx/ui/androidview/demos/WebComponentActivity.kt
M       ui/ui-animation/src/main/java/androidx/ui/animation/AnimatedValueEffects.kt
M       ui/ui-animation/src/main/java/androidx/ui/animation/Transition.kt
M       ui/ui-core/src/androidTest/java/androidx/ui/core/test/AndroidLayoutDrawTest.kt
M       ui/ui-core/src/androidTest/java/androidx/ui/core/test/AndroidViewCompatTest.kt
M       ui/ui-core/src/androidTest/java/androidx/ui/core/test/ClipTest.kt
M       ui/ui-core/src/androidTest/java/androidx/ui/core/test/DrawShadowTest.kt
M       ui/ui-core/src/androidTest/java/androidx/ui/core/test/ModelReadsTest.kt
M       ui/ui-core/src/androidTest/java/androidx/ui/core/test/OpacityTest.kt
D       ui/ui-core/src/androidTest/java/androidx/ui/core/test/ValueModel.kt
M       ui/ui-core/src/androidTest/java/androidx/ui/core/test/WithConstraintsTest.kt
M       ui/ui-core/src/androidTest/java/androidx/ui/res/ResourcesTest.kt
M       ui/ui-core/src/androidTest/java/androidx/ui/semantics/SemanticsTests.kt
M       ui/ui-core/src/main/java/androidx/ui/core/ModelObserver.kt
M       ui/ui-core/src/main/java/androidx/ui/res/Resources.kt
M       ui/ui-core/src/test/java/androidx/ui/core/selection/SelectionManagerDragTest.kt
M       ui/ui-core/src/test/java/androidx/ui/core/selection/SelectionManagerLongPressDragTest.kt
M       ui/ui-core/src/test/java/androidx/ui/core/selection/SelectionManagerTest.kt
M       ui/ui-foundation/src/androidTest/java/androidx/ui/foundation/DeterminateProgressTest.kt
M       ui/ui-layout/src/androidTest/java/androidx/ui/layout/test/ContainerTest.kt
M       ui/ui-layout/src/androidTest/java/androidx/ui/layout/test/OnPositionedTest.kt
M       ui/ui-material/api/0.1.0-dev12.txt
M       ui/ui-material/api/current.txt
M       ui/ui-material/api/public_plus_experimental_0.1.0-dev12.txt
M       ui/ui-material/api/public_plus_experimental_current.txt
M       ui/ui-material/api/restricted_0.1.0-dev12.txt
M       ui/ui-material/api/restricted_current.txt
M       ui/ui-material/integration-tests/material-demos/src/main/java/androidx/ui/material/demos/DynamicThemeActivity.kt
M       ui/ui-material/src/androidTest/java/androidx/ui/material/DrawerTest.kt
M       ui/ui-material/src/androidTest/java/androidx/ui/material/ProgressIndicatorTest.kt
M       ui/ui-material/src/androidTest/java/androidx/ui/material/RadioGroupUiTest.kt
M       ui/ui-material/src/main/java/androidx/ui/material/Color.kt
M       ui/ui-material/src/main/java/androidx/ui/material/Scaffold.kt
M       ui/ui-test/src/androidTest/java/androidx/ui/test/AndroidComposeTestCaseRunnerTest.kt
M       ui/ui-test/src/androidTest/java/androidx/ui/test/MultipleComposeRootsTest.kt
M       ui/ui-text/src/main/java/androidx/ui/text/CoreText.kt
M       ui/ui-text/src/main/java/androidx/ui/text/CoreTextField.kt

https://android-review.googlesource.com/1311293

Project: platform/frameworks/support
Branch: androidx-main

commit dd000ea5e6eb3a8f07b869595ca62aa2fb781d12
Author: Andrey Kulikov <andreykulikov@google.com>
Date:   Mon Feb 22 19:42:13 2021

    Fix for broken rememberSaveable { mutableStateOf(0) } with navigation-compose
   
    Previously we were converting MutableState into a parcelable structure only for a direct child of the saving list. It was incorrect as SaveableStateHolder used in navigation is wrapping the state of the screen as a value into a Map. Now we will recursively iterate through List/Maps and covert all inner MutableState objects.
   
    Fixes: 180042685
    Fixes: 180701630
    Test: new tests in ActivityRecreationTest
    Relnote: Fix for broken rememberSaveable { mutableStateOf(0) } when used inside a destination of navigation-compose.
    Change-Id: I1312b5b210dde32250945d164a2f3a1b574cb0a8

M       compose/runtime/runtime-saveable/src/androidAndroidTest/AndroidManifest.xml
M       compose/runtime/runtime-saveable/src/androidAndroidTest/kotlin/androidx/compose/runtime/saveable/ActivityRecreationTest.kt
M       compose/runtime/runtime-saveable/src/commonMain/kotlin/androidx/compose/runtime/saveable/RememberSaveable.kt
M       compose/ui/ui/src/androidMain/kotlin/androidx/compose/ui/platform/DisposableSaveableStateRegistry.android.kt

https://android-review.googlesource.com/1599261

Thanks for reporting. The fix will be released in beta02

Can you share more details?

ParcelableSnapshotMutableState is Parcelable, not sure how it is possible that it can't be written to Parcel.

If you can file a new bug with the reproducible code sample we will be able to take a look

Hey, I'm also having same kinda problem:

  E  FATAL EXCEPTION: main
                                                                                                    Process: com.example.animeapp, PID: 12273
                                                                                                    java.lang.RuntimeException: Parcel: unable to marshal value Color(0.83137256, 0.75686276, 0.8156863, 1.0, sRGB IEC61966-2.1)
                                                                                                        at android.os.Parcel.writeValue(Parcel.java:1885)
                                                                                                        at android.os.Parcel.writeList(Parcel.java:1092)
                                                                                                        at android.os.Parcel.writeValue(Parcel.java:1832)
                                                                                                        at android.os.Parcel.writeList(Parcel.java:1092)
                                                                                                        at android.os.Parcel.writeValue(Parcel.java:1832)
                                                                                                        at android.os.Parcel.writeMapInternal(Parcel.java:943)
                                                                                                        at android.os.Parcel.writeMap(Parcel.java:925)
                                                                                                        at android.os.Parcel.writeValue(Parcel.java:1797)
                                                                                                        at android.os.Parcel.writeMapInternal(Parcel.java:943)
                                                                                                        at android.os.Parcel.writeMap(Parcel.java:925)
                                                                                                        at android.os.Parcel.writeValue(Parcel.java:1797)
                                                                                                        at android.os.Parcel.writeList(Parcel.java:1092)
                                                                                                        at android.os.Parcel.writeValue(Parcel.java:1832)
                                                                                                        at android.os.Parcel.writeArrayMapInternal(Parcel.java:975)
                                                                                                        at android.os.BaseBundle.writeToParcelInner(BaseBundle.java:1620)
                                                                                                        at android.os.Bundle.writeToParcel(Bundle.java:1303)
                                                                                                        at android.os.Parcel.writeBundle(Parcel.java:1044)
                                                                                                        at android.os.Parcel.writeValue(Parcel.java:1801)
                                                                                                        at android.os.Parcel.writeArrayMapInternal(Parcel.java:975)
                                                                                                        at android.os.BaseBundle.writeToParcelInner(BaseBundle.java:1620)
                                                                                                        at android.os.Bundle.writeToParcel(Bundle.java:1303)
                                                                                                        at android.os.Parcel.writeBundle(Parcel.java:1044)
                                                                                                        at android.os.Parcel.writeValue(Parcel.java:1801)
                                                                                                        at android.os.Parcel.writeArrayMapInternal(Parcel.java:975)
                                                                                                        at android.os.BaseBundle.writeToParcelInner(BaseBundle.java:1620)
                                                                                                        at android.os.Bundle.writeToParcel(Bundle.java:1303)
                                                                                                        at android.app.IActivityTaskManager$Stub$Proxy.activityStopped(IActivityTaskManager.java:4389)
                                                                                                        at android.app.servertransaction.PendingTransactionActions$StopInfo.run(PendingTransactionActions.java:145)
                                                                                                        at android.os.Handler.handleCallback(Handler.java:938)
                                                                                                        at android.os.Handler.dispatchMessage(Handler.java:99)
                                                                                                        at android.os.Looper.loop(Looper.java:223)
                                                                                                        at android.app.ActivityThread.main(ActivityThread.java:7656)
                                                                                                        at java.lang.reflect.Method.invoke(Native Method)
                                                                                                        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
                                                                                                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)

Color is not automatically saveable, you need to write a custom Saver which will convert it to primitive and then back