feat(ios): add data binding replace view model instance support

## Changes
- Adds support for replacing view model instance properties with other view model instances

## Fixes
- Fixes an issue where nested view model instances and properties were getting incorrectly created and cached

Diffs=
909ae012c1 feat(ios): add data binding replace view model instance support (#9500)

Co-authored-by: David Skuza <david@rive.app>

.rive_head

@@ -1 +1 @@
-598ad6c62e7b56024c97dad252774e5b935353c1
+909ae012c1e5c721d473e997fa61976a23acb768

Source/DataBinding/RiveDataBindingViewModelInstance.h

@@ -131,6 +131,21 @@ NS_SWIFT_NAME(RiveDataBindingViewModel.Instance)
 - (nullable RiveDataBindingViewModelInstance*)viewModelInstancePropertyFromPath:
     (NSString*)path;
 
+/// Replaces a view model property of the view model instance with another
+/// instance.
+///
+/// - Parameters:
+///   - path: The path to the view model property to replace.
+///   - instance: The instance to replace the view model property at `path`
+///   with.
+///
+/// - Returns: `true` if the view model instance was replaced, otherwise
+/// `false`.
+- (BOOL)setViewModelInstancePropertyFromPath:(NSString*)path
+                                  toInstance:(RiveDataBindingViewModelInstance*)
+                                                 instance
+    NS_SWIFT_NAME(setViewModelInstanceProperty(fromPath:to:));
+
 /// Returns a trigger property in the view model instance.
 ///
 /// - Note: Unlike a `RiveViewModel.Instance`, a strong reference to this type

Source/DataBinding/RiveDataBindingViewModelInstance.mm

@@ -264,7 +264,18 @@
 - (RiveDataBindingViewModelInstance*)viewModelInstancePropertyFromPath:
     (NSString*)path
 {
-    return [self childForPath:path];
+    RiveDataBindingViewModelInstance* parent = [self parentForPath:path];
+    return
+        [parent viewModelInstanceWithName:[[path pathComponents] lastObject]];
+}
+
+- (BOOL)setViewModelInstancePropertyFromPath:(NSString*)path
+                                  toInstance:(RiveDataBindingViewModelInstance*)
+                                                 instance
+{
+    RiveDataBindingViewModelInstance* parent = [self parentForPath:path];
+    return [parent setViewModelInstance:instance
+                                forName:[path lastPathComponent]];
 }
 
 - (RiveDataBindingViewModelInstanceTriggerProperty*)triggerPropertyFromPath:
@@ -341,29 +352,14 @@
 - (void)cacheProperty:(RiveDataBindingViewModelInstanceProperty*)value
              withPath:(NSString*)path
 {
-    NSArray<NSString*>* components = [path pathComponents];
-    if (components.count == 1)
-    {
-        _properties[path] = value;
-    }
-    else
-    {
-        RiveDataBindingViewModelInstance* child =
-            [self childForPath:components[0]];
-        if (child)
-        {
-            NSArray* subcomponents = [components
-                subarrayWithRange:NSMakeRange(1, components.count - 1)];
-            NSString* subpath = [subcomponents componentsJoinedByString:@"/"];
-            [child cacheProperty:value withPath:subpath];
-        }
-    }
+    RiveDataBindingViewModelInstance* parent = [self parentForPath:path];
+    [parent setProperty:value forName:[path lastPathComponent]];
 }
 
 - (nullable id)cachedPropertyFromPath:(NSString*)path asClass:(Class)aClass
 {
-    RiveDataBindingViewModelInstanceProperty* property =
-        [_properties objectForKey:path];
+    RiveDataBindingViewModelInstance* parent = [self parentForPath:path];
+    id property = [parent cachedPropertyWithName:[path lastPathComponent]];
     if (property != nil && [property isKindOfClass:aClass])
     {
         return property;
@@ -384,47 +380,68 @@
 
 #pragma mark - Paths
 
-- (nullable RiveDataBindingViewModelInstance*)childForPath:(NSString*)path
+- (nullable RiveDataBindingViewModelInstance*)parentForPath:(NSString*)path
 {
-    NSArray* components = [path pathComponents];
-    // If we have no components, we have no child to add
-    if (components.count == 0)
+    NSArray* pathComponents = [path pathComponents];
+
+    if (pathComponents.count == 0)
     {
         return nil;
     }
 
-    // E.g from "current/path", this is "current".
-    // If a child exists with that name, return it.
-    NSString* currentPath = components[0];
-    // Use map over set
-    RiveDataBindingViewModelInstance* existing = nil;
-    if ((existing = [_children objectForKey:currentPath]))
+    if (pathComponents.count == 1)
+    {
+        return self;
+    }
+
+    NSArray* subpathComponents = [pathComponents
+        subarrayWithRange:NSMakeRange(1, pathComponents.count - 1)];
+    RiveDataBindingViewModelInstance* instance =
+        [self viewModelInstanceWithName:[pathComponents firstObject]];
+    return [instance
+        parentForPath:[subpathComponents componentsJoinedByString:@"/"]];
+}
+
+- (nullable RiveDataBindingViewModelInstance*)viewModelInstanceWithName:
+    (NSString*)name
+{
+    RiveDataBindingViewModelInstance* existing;
+    if ((existing = _children[name]))
     {
         return existing;
     }
-
-    // Otherwise, for the current path, build a tree recursively, starting with
-    // the current position.
-    auto instance =
-        _instance->propertyViewModel(std::string([currentPath UTF8String]));
-    if (instance == nullptr)
+    auto i = _instance->propertyViewModel(std::string([name UTF8String]));
+    if (i == nullptr)
     {
         return nil;
     }
+    RiveDataBindingViewModelInstance* instance =
+        [[RiveDataBindingViewModelInstance alloc] initWithInstance:i];
+    _children[name] = instance;
+    return instance;
+}
 
-    RiveDataBindingViewModelInstance* child =
-        [[RiveDataBindingViewModelInstance alloc] initWithInstance:instance];
-    _children[currentPath] = child;
-    if (components.count == 1)
+- (BOOL)setViewModelInstance:(RiveDataBindingViewModelInstance*)instance
+                     forName:(NSString*)name
+{
+    BOOL replaced = _instance->replaceViewModelByName(
+        std::string([name UTF8String]), instance.instance);
+    if (replaced)
     {
-        return child;
-    }
-    else
-    {
-        NSArray* subpath =
-            [components subarrayWithRange:NSMakeRange(1, components.count - 1)];
-        return [self childForPath:[subpath componentsJoinedByString:@"/"]];
+        _children[name] = instance;
     }
+    return replaced;
+}
+
+- (id)cachedPropertyWithName:(NSString*)name
+{
+    return [_properties objectForKey:name];
+}
+
+- (void)setProperty:(RiveDataBindingViewModelInstanceProperty*)property
+            forName:(NSString*)name
+{
+    _properties[name] = property;
 }
 
 @end

Tests/DataBindingTests.swift

@@ -380,6 +380,58 @@ class DataBindingTests: XCTestCase {
         XCTAssertEqual(nestedProperty!.value, newValue)
     }
 
+    func test_viewModelInstance_nested_areIdentical() {
+        let instance = file.viewModelNamed("Test")!.createDefaultInstance()!
+
+        let fromPath = instance.viewModelInstanceProperty(fromPath: "Nested/DeeperNested")!
+        let nested = instance.viewModelInstanceProperty(fromPath: "Nested")!.viewModelInstanceProperty(fromPath: "DeeperNested")!
+        XCTAssertIdentical(fromPath, nested)
+    }
+
+    func test_viewModelInstance_replace_withCorrectInstance_setsNewInstance() throws {
+        let instance = file.viewModelNamed("Test")!.createDefaultInstance()!
+        XCTAssertEqual(instance.stringProperty(fromPath: "Nested/String")!.value, "Nested")
+
+//         Test one-level deep + caching
+        let replacement = file.viewModelNamed("Nested")!.createInstance()!
+        replacement.stringProperty(fromPath: "String")!.value = "Hello, Rive"
+        var replaced = instance.setViewModelInstanceProperty(fromPath: "Nested", to: replacement)
+        XCTAssertTrue(replaced)
+        XCTAssertEqual(instance.stringProperty(fromPath: "Nested/String")!.value, "Hello, Rive")
+        XCTAssertIdentical(
+            instance.viewModelInstanceProperty(fromPath: "Nested"),
+            replacement
+        )
+
+//         Test two-level deep traversal + caching
+        let nestedReplacement = file.viewModelNamed("Default")!.createDefaultInstance()!
+        replaced = instance.setViewModelInstanceProperty(fromPath: "Nested/DeeperNested", to: nestedReplacement)
+        XCTAssertTrue(replaced)
+        XCTAssertIdentical(
+            instance.viewModelInstanceProperty(fromPath: "Nested/DeeperNested")!,
+            nestedReplacement
+        )
+
+        XCTAssertIdentical(
+            instance.viewModelInstanceProperty(fromPath: "Nested/DeeperNested")!,
+            instance.viewModelInstanceProperty(fromPath: "Nested")!.viewModelInstanceProperty(fromPath: "DeeperNested")
+        )
+
+        XCTAssertEqual(
+            instance.stringProperty(fromPath: "Nested/DeeperNested/String")!.value,
+            instance.viewModelInstanceProperty(fromPath: "Nested")!
+                .viewModelInstanceProperty(fromPath: "DeeperNested")!
+                .stringProperty(fromPath: "String")!.value
+        )
+    }
+
+    func test_viewModelInstance_replace_withIncorrectInstance_returnsFalse() throws {
+        let instance = file.viewModelNamed("Test")!.createDefaultInstance()!
+        let replacement = file.viewModelNamed("Default")!.createInstance()!
+        let replaced = instance.setViewModelInstanceProperty(fromPath: "Nested", to: replacement)
+        XCTAssertFalse(replaced)
+    }
+
     // MARK: Trigger
 
     func test_viewModelInstance_triggerProperty_returnsPropertyOrNil() {
@@ -957,16 +1009,6 @@ class DataBindingTests: XCTestCase {
         wait(for: [expectation], timeout: 1)
     }
 
-    func test_nestedViewModel_property_createsAndCachesChildren() throws {
-        let instance = file.viewModelNamed("Test")!.createDefaultInstance()!
-        let nested: RiveDataBindingViewModel.Instance? = instance.viewModelInstanceProperty(fromPath: "Nested")!
-        let nestedCopy = instance.viewModelInstanceProperty(fromPath: "Nested")!
-        XCTAssertTrue(nested === nestedCopy)
-
-        let fullPath = instance.viewModelInstanceProperty(fromPath: "Nested/Nested")
-        XCTAssertTrue(nestedCopy === fullPath)
-    }
-
     func test_instance_property_whenBoundToTwoStateMachines_ifNoAdditionalChanges_callsListenerOnce() throws {
         let instance = file.viewModelNamed("Test")!.createDefaultInstance()!