Fabric: `-[RCTViewComponentView setContentView:]`:

Summary:
This is just the convenient way to embed native views inside custom View components.
See coming <Switch> implementation as an example.

Reviewed By: fkgozali

Differential Revision: D8344056

fbshipit-source-id: 7f5f8cfeeffa7676bc7b562aa07f006cb9006575

React/Fabric/Mounting/ComponentViews/View/RCTViewComponentView.h

@@ -26,6 +26,16 @@ NS_ASSUME_NONNULL_BEGIN
   facebook::react::SharedViewEventEmitter _eventEmitter;
 }
 
+/**
+ * Represents the `UIView` instance that is being automatically attached to
+ * the component view and laid out using on `layoutMetrics` (especially `size`
+ * and `padding`) of the component.
+ * This view must not be a component view; it's just a convenient way
+ * to embed/bridge pure native views as component views.
+ * Defaults to `nil`. Assing `nil` to remove view as subview.
+ */
+@property (nonatomic, strong, nullable) UIView *contentView;
+
 @end
 
 NS_ASSUME_NONNULL_END

React/Fabric/Mounting/ComponentViews/View/RCTViewComponentView.mm

@@ -14,6 +14,28 @@
 using namespace facebook::react;
 
 @implementation RCTViewComponentView
+- (void)setContentView:(UIView *)contentView
+{
+  if (_contentView) {
+    [_contentView removeFromSuperview];
+  }
+
+  _contentView = contentView;
+
+  if (_contentView) {
+    [self addSubview:_contentView];
+  }
+}
+
+- (void)layoutSubviews
+{
+  [super layoutSubviews];
+
+  if (_contentView) {
+    _contentView.frame = RCTCGRectFromRect(_layoutMetrics.getContentFrame());
+  }
+}
+
 
 - (void)updateProps:(SharedProps)props
            oldProps:(SharedProps)oldProps
@@ -42,9 +64,10 @@ using namespace facebook::react;
 - (void)updateLayoutMetrics:(LayoutMetrics)layoutMetrics
            oldLayoutMetrics:(LayoutMetrics)oldLayoutMetrics
 {
+  _layoutMetrics = layoutMetrics;
+
   [super updateLayoutMetrics:layoutMetrics oldLayoutMetrics:oldLayoutMetrics];
 
-  _layoutMetrics = layoutMetrics;
 }
 
 #pragma mark - Accessibility Events