Add minimumSize to RCTRootView & RCTRootShadowView

Summary:
This adds a `minimumSize` property to RCTRootView, and forwards any changes to it's shadow view. This **does not** change any default behaviour, as the default minimum size is `CGSizeZero` before & after this diff.

Changelog: [iOS][Internal] Add minimumSize to RCTRootView & RCTRootShadowView

Reviewed By: RSNara

Differential Revision: D20905456

fbshipit-source-id: a03f880e782891f60ef86b9c898965e05a5e796e

Author: Peter Argany

React/Base/RCTRootView.h

@@ -94,6 +94,11 @@ extern
  */
 @property (nonatomic, assign) RCTRootViewSizeFlexibility sizeFlexibility;
 
+/*
+ * The minimum size of the root view, defaults to CGSizeZero.
+ */
+@property (nonatomic, assign) CGSize minimumSize;
+
 /**
  * The delegate that handles intrinsic size updates.
  */

React/Base/RCTRootView.m

@@ -21,6 +21,7 @@
 #import "RCTPerformanceLogger.h"
 #import "RCTProfile.h"
 #import "RCTRootContentView.h"
+#import "RCTRootShadowView.h"
 #import "RCTTouchHandler.h"
 #import "RCTUIManager.h"
 #import "RCTUIManagerUtils.h"
@@ -71,6 +72,7 @@ - (instancetype)initWithBridge:(RCTBridge *)bridge
     _loadingViewFadeDelay = 0.25;
     _loadingViewFadeDuration = 0.25;
     _sizeFlexibility = RCTRootViewSizeFlexibilityNone;
+    _minimumSize = CGSizeZero;
 
     [[NSNotificationCenter defaultCenter] addObserver:self
                                              selector:@selector(bridgeDidReload)
@@ -167,6 +169,23 @@ - (void)layoutSubviews
   _loadingView.center = (CGPoint){CGRectGetMidX(self.bounds), CGRectGetMidY(self.bounds)};
 }
 
+- (void)setMinimumSize:(CGSize)minimumSize
+{
+  if (CGSizeEqualToSize(_minimumSize, minimumSize)) {
+    return;
+  }
+  _minimumSize = minimumSize;
+  __block NSNumber *tag = self.reactTag;
+  __weak typeof(self) weakSelf = self;
+  RCTExecuteOnUIManagerQueue(^{
+    __strong typeof(self) strongSelf = weakSelf;
+    if (strongSelf && strongSelf->_bridge.isValid) {
+      RCTRootShadowView *shadowView = (RCTRootShadowView *)[strongSelf->_bridge.uiManager shadowViewForReactTag:tag];
+      shadowView.minimumSize = minimumSize;
+    }
+  });
+}
+
 - (UIViewController *)reactViewController
 {
   return _reactViewController ?: [super reactViewController];

React/Views/RCTRootShadowView.h

@@ -10,6 +10,12 @@
 
 @interface RCTRootShadowView : RCTShadowView
 
+/**
+ * Minimum size to layout all views.
+ * Defaults to CGSizeZero
+ */
+@property (nonatomic, assign) CGSize minimumSize;
+
 /**
  * Available size to layout all views.
  * Defaults to {INFINITY, INFINITY}

React/Views/RCTRootShadowView.m

@@ -16,6 +16,7 @@ - (instancetype)init
 {
   if (self = [super init]) {
     _baseDirection = [[RCTI18nUtil sharedInstance] isRTL] ? YGDirectionRTL : YGDirectionLTR;
+    _minimumSize = CGSizeZero;
     _availableSize = CGSizeMake(INFINITY, INFINITY);
   }
 
@@ -31,7 +32,7 @@ - (void)layoutWithAffectedShadowViews:(NSHashTable<RCTShadowView *> *)affectedSh
   layoutContext.affectedShadowViews = affectedShadowViews;
   layoutContext.other = other;
 
-  [self layoutWithMinimumSize:CGSizeZero
+  [self layoutWithMinimumSize:_minimumSize
                   maximumSize:_availableSize
               layoutDirection:RCTUIKitLayoutDirectionFromYogaLayoutDirection(_baseDirection)
                 layoutContext:layoutContext];