Add several SavedStateHandle delegates.

app/src/main/java/org/thoughtcrime/securesms/linkpreview/LinkPreviewViewModelV2.kt

@@ -16,6 +16,7 @@ import org.signal.core.util.Result
 import org.signal.core.util.isAbsent
 import org.thoughtcrime.securesms.keyvalue.SignalStore
 import org.thoughtcrime.securesms.util.Debouncer
+import org.thoughtcrime.securesms.util.delegate
 import org.thoughtcrime.securesms.util.rx.RxStore
 import java.util.Optional
 
@@ -35,7 +36,8 @@ class LinkPreviewViewModelV2(
   }
 
   private var enabled = SignalStore.settings().isLinkPreviewsEnabled
-  private val linkPreviewStateStore = RxStore(savedStateHandle[LINK_PREVIEW_STATE] ?: LinkPreviewState.forNoLinks())
+  private var savedLinkPreviewState by savedStateHandle.delegate(LINK_PREVIEW_STATE) { LinkPreviewState.forNoLinks() }
+  private val linkPreviewStateStore = RxStore(savedLinkPreviewState)
 
   val linkPreviewState: Flowable<LinkPreviewState> = linkPreviewStateStore.stateFlowable.observeOn(AndroidSchedulers.mainThread())
   val linkPreviewStateSnapshot: LinkPreviewState = linkPreviewStateStore.state
@@ -43,16 +45,8 @@ class LinkPreviewViewModelV2(
   val hasLinkPreview: Boolean = linkPreviewStateStore.state.linkPreview.isPresent
   val hasLinkPreviewUi: Boolean = linkPreviewStateStore.state.hasContent()
 
-  private var activeUrl: String?
-    get() = savedStateHandle[ACTIVE_URL]
-    set(value) {
-      savedStateHandle[ACTIVE_URL] = value
-    }
-  private var userCancelled: Boolean
-    get() = savedStateHandle[USER_CANCELLED] ?: false
-    set(value) {
-      savedStateHandle[USER_CANCELLED] = value
-    }
+  private var activeUrl: String? by savedStateHandle.delegate(ACTIVE_URL)
+  private var userCancelled: Boolean by savedStateHandle.delegate(USER_CANCELLED, false)
 
   private var activeRequest: Disposable = Disposable.disposed()
   private val debouncer: Debouncer = Debouncer(250)
@@ -61,7 +55,7 @@ class LinkPreviewViewModelV2(
     .stateFlowable
     .observeOn(AndroidSchedulers.mainThread())
     .subscribeBy {
-      savedStateHandle[LINK_PREVIEW_STATE] = it
+      savedLinkPreviewState = it
     }
 
   override fun onCleared() {

app/src/main/java/org/thoughtcrime/securesms/util/SavedStateHandleExtensions.kt

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2023 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.thoughtcrime.securesms.util
+
+import androidx.lifecycle.SavedStateHandle
+import kotlin.properties.ReadWriteProperty
+import kotlin.reflect.KProperty
+
+/**
+ * Nullable SavedStateHandle delegate, which does not accept a default.
+ */
+fun <T> SavedStateHandle.delegate(key: String): ReadWriteProperty<Any?, T?> {
+  return NullableSavedStateHandleDelegate(this, key)
+}
+
+/**
+ * Non-null SavedStateHandle delegate with a default value. Recommended when the default
+ * value has to be created on-demand. The default is NOT written to the SavedStateHandle.
+ */
+fun <T> SavedStateHandle.delegate(key: String, default: () -> T): ReadWriteProperty<Any?, T> {
+  return DefaultSavedStateHandleDelegate(this, key, default)
+}
+
+/**
+ * Convenience function for non-null SavedStateHandle delegate. Recommended when working
+ * with primitive or pre-constructed objects. The default is NOT written to the SavedStateHandle.
+ */
+fun <T> SavedStateHandle.delegate(key: String, default: T): ReadWriteProperty<Any?, T> {
+  return DefaultSavedStateHandleDelegate(this, key) { default }
+}
+
+private class NullableSavedStateHandleDelegate<T>(
+  private val handle: SavedStateHandle,
+  private val key: String
+) : ReadWriteProperty<Any?, T?> {
+  override operator fun getValue(thisRef: Any?, property: KProperty<*>): T? {
+    return handle[key]
+  }
+
+  override operator fun setValue(thisRef: Any?, property: KProperty<*>, value: T?) {
+    handle[key] = value
+  }
+}
+
+private class DefaultSavedStateHandleDelegate<T>(
+  private val handle: SavedStateHandle,
+  private val key: String,
+  default: () -> T
+) : ReadWriteProperty<Any?, T> {
+
+  private val lazyDefault by lazy { default() }
+
+  override operator fun getValue(thisRef: Any?, property: KProperty<*>): T {
+    return handle[key] ?: lazyDefault
+  }
+
+  override operator fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
+    handle[key] = value
+  }
+}