Expose forceLayout in EpoxySwiftUIHostingView (#172)

* Expose `forceLayout` in EpoxySwiftUIHostingView

* Add comments

---------

Co-authored-by: Shengqi Zhu <shengqi.zhu@airbnb.com>

Author: zetasq

CHANGELOG.md

@@ -6,6 +6,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased](https://github.com/airbnb/epoxy-ios/compare/0.10.0...HEAD)
 
+### Added
+- Expose `forceLayout` in `EpoxySwiftUIHostingView` for updating the hosting view size from outside.
+
 ### Changed
 - `AnyItemModel` now implements the `ErasedContentProviding` protocol.
 - Updated `ErasedContentProviding` protocol to use its type name instead of `Self` in the keys of its `EpoxyModelProperty` properties `contentProperty` and `isContentEqualProperty `.

Sources/EpoxyCore/SwiftUI/EpoxySwiftUIHostingView.swift

@@ -198,12 +198,9 @@ public final class EpoxySwiftUIHostingView<RootView: View>: UIView, EpoxyableVie
     // The view controller must be added to the view controller hierarchy to measure its content.
     addViewControllerIfNeededAndReady()
 
-    // We need to layout the view to ensure it gets resized properly when cells are re-used
-    viewController.view.setNeedsLayout()
-    viewController.view.layoutIfNeeded()
-
-    // This is required to ensure that views with new content are properly resized.
-    viewController.view.invalidateIntrinsicContentSize()
+    // In this method `setNeedsLayout` and `layoutIfNeeded` are called. We need to layout the view to ensure it gets resized properly when cells are re-used
+    // In this method `invalidateIntrinsicContentSize` is called. This is required to ensure that views with new content are properly resized.
+    forceLayout()
   }
 
   public override func layoutMarginsDidChange() {
@@ -234,9 +231,7 @@ public final class EpoxySwiftUIHostingView<RootView: View>: UIView, EpoxyableVie
       // to be more common with top and bottom bars, since they can be laid out early during view
       // controller transitions. If this works well, we may make this the default behavior for all
       // SwiftUI views.
-      viewController.view.setNeedsLayout()
-      viewController.view.layoutIfNeeded()
-      viewController.view.invalidateIntrinsicContentSize()
+      forceLayout()
     } else {
       // Allow the layout margins update to fully propagate through to the SwiftUI View before
       // invalidating the layout.
@@ -246,6 +241,14 @@ public final class EpoxySwiftUIHostingView<RootView: View>: UIView, EpoxyableVie
     }
   }
 
+  /// Force relayout the UIHostingView and invalidate its intrinsic content size.
+  /// This is used for updating the view size manually.
+  public func forceLayout() {
+    viewController.view.setNeedsLayout()
+    viewController.view.layoutIfNeeded()
+    viewController.view.invalidateIntrinsicContentSize()
+  }
+
   public func handleWillDisplay(animated: Bool) {
     guard state != .appeared, window != nil else { return }
     transition(to: .appearing(animated: animated))