readingGeometry modifier (#44)

Sources/SwiftUISupportSizing/View+MeasureSize.swift

@@ -0,0 +1,71 @@
+import SwiftUI
+
+private struct SizingPreferenceKey: PreferenceKey {
+
+  typealias Value = CGSize
+
+  static var defaultValue: Value = .zero
+
+  static func reduce(value: inout Value, nextValue: () -> Value) {
+    let next = nextValue()
+    value = next
+  }
+
+}
+
+extension View {
+
+  /**
+   Measures the receiver view size using GeometryReader.
+   
+   !! Should be deprecated in favor of using directly ``readingGeometry(transform:target:)``
+   */
+  public func measureSize(_ size: Binding<CGSize>) -> some View {
+    readingGeometry(transform: \.size, target: size)
+  }
+
+}
+
+private enum GeometryReaderPreferenceKey<Projected: Equatable>: PreferenceKey {
+
+  static var defaultValue: Projected? {
+    return nil
+  }
+
+  static func reduce(value: inout Value, nextValue: () -> Projected?) {
+    let next = nextValue()
+    value = next
+  }
+
+}
+
+extension View {
+
+  public consuming func readingGeometry<Projected: Equatable>(
+    transform: @escaping (GeometryProxy) -> Projected,
+    target: Binding<Projected>
+  ) -> some View {
+    readingGeometry(transform: transform, onChange: {
+      target.wrappedValue = $0
+    })
+  }
+
+  public consuming func readingGeometry<Projected: Equatable>(
+    transform: @escaping (GeometryProxy) -> Projected,
+    onChange: @escaping (Projected) -> Void
+  ) -> some View {
+    background(
+      Color.clear.background(
+        GeometryReader(content: { proxy in
+          Color.clear
+            .preference(key: GeometryReaderPreferenceKey<Projected>.self, value: transform(proxy))
+        })
+      )
+      .onPreferenceChange(GeometryReaderPreferenceKey<Projected>.self) { projected in
+        guard let projected else { return }
+        onChange(projected)
+      }
+    )
+  }
+
+}