Add support for setting default HeaderFooter properties via HeaderFoo…

…terContent's defaultHeaderFooterProperties.

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 ### Added
 
+- [Introduce `defaultHeaderFooterProperties` on `HeaderFooterContent`](https://github.com/kyleve/Listable/pull/304), to allow specifying default values for a `HeaderFooter` when values are not passed to the initializer.
+
 ### Removed
 
 ### Changed

Demo/Sources/Demos/Demo Screens/AutoLayoutDemoViewController.swift

@@ -38,7 +38,7 @@ struct AutoLayoutContent : ItemContent, Equatable {
         header + detail
     }
 
-    var defaultItemProperties: DefaultItemProperties<Self> {
+    var defaultItemProperties: DefaultProperties {
         .init(
             sizing: .autolayout()
         )

ListableUI/Sources/HeaderFooter/DefaultHeaderFooterProperties.swift

@@ -0,0 +1,32 @@
+//
+//  DefaultHeaderFooterProperties.swift
+//  ListableUI
+//
+//  Created by Kyle Van Essen on 6/27/21.
+//
+
+import Foundation
+
+
+/// Allows specifying default properties to apply to a header / footer when it is initialized,
+/// if those values are not provided to the initializer.
+/// Only non-nil values are used – if you do not want to provide a default value,
+/// simply leave the property nil.
+///
+/// The order of precedence used when assigning values is:
+/// 1) The value passed to the initializer.
+/// 2) The value from `defaultHeaderFooterProperties` on the contained `HeaderFooterContent`, if non-nil.
+/// 3) A standard, default value.
+public struct DefaultHeaderFooterProperties<Content:HeaderFooterContent>
+{
+    public var sizing : Sizing?
+    public var layouts : HeaderFooterLayouts?
+
+    public init(
+        sizing : Sizing? = nil,
+        layouts : HeaderFooterLayouts? = nil
+    ) {
+        self.sizing = sizing
+        self.layouts = layouts
+    }
+}

ListableUI/Sources/HeaderFooter/HeaderFooter.swift

@@ -41,16 +41,18 @@ public struct HeaderFooter<Content:HeaderFooterContent> : AnyHeaderFooter
 
     public init(
         _ content : Content,
-        sizing : Sizing = .thatFits(.init(.atLeast(.default))),
-        layouts : HeaderFooterLayouts = .init(),
+        sizing : Sizing? = nil,
+        layouts : HeaderFooterLayouts? = nil,
         onTap : OnTap? = nil
     ) {
         assertIsValueType(Content.self)
 
         self.content = content
 
-        self.sizing = sizing
-        self.layouts = layouts
+        let defaults = self.content.defaultHeaderFooterProperties
+
+        self.sizing = finalValue(from: sizing, defaults.sizing, .thatFits(.init(.atLeast(.default))))
+        self.layouts = finalValue(from: layouts, defaults.layouts, .init())
 
         self.onTap = onTap
 
@@ -110,3 +112,19 @@ extension HeaderFooter : SignpostLoggable
         )
     }
 }
+
+
+private func finalValue<Value>(
+    from provided : Value?,
+    _ contentDefault : Value?,
+    _ default : @autoclosure () -> Value
+) -> Value
+{
+    if let value = provided {
+        return value
+    } else if let value = contentDefault {
+        return value
+    } else {
+        return `default`()
+    }
+}

ListableUI/Sources/HeaderFooter/HeaderFooterContent.swift

@@ -43,7 +43,23 @@ public typealias FooterContent = HeaderFooterContent
 /// z-Index 1) `BackgroundView`
 ///
 public protocol HeaderFooterContent
-{    
+{
+    //
+    // MARK: Tracking Changes
+    //
+
+    func isEquivalent(to other : Self) -> Bool
+
+    //
+    // MARK: Default Properties
+    //
+
+    typealias DefaultProperties = DefaultHeaderFooterProperties<Self>
+
+    /// Default values to assign to various properties on the `HeaderFooter` which wraps
+    /// this `HeaderFooterContent`, if those values are not passed to the `HeaderFooter` initializer.
+    var defaultHeaderFooterProperties : DefaultProperties { get }
+
     //
     // MARK: Applying To Displayed View
     //
@@ -54,12 +70,6 @@ public protocol HeaderFooterContent
         with info : ApplyHeaderFooterContentInfo
     )
 
-    //
-    // MARK: Tracking Changes
-    //
-
-    func isEquivalent(to other : Self) -> Bool
-
     //
     // MARK: Creating & Providing Content Views
     //
@@ -173,10 +183,21 @@ public extension HeaderFooterContent where Self.BackgroundView == UIView
     }
 }
 
+
 public extension HeaderFooterContent where Self.PressedBackgroundView == UIView
 {
     static func createReusablePressedBackgroundView(frame : CGRect) -> PressedBackgroundView
     {
         PressedBackgroundView(frame: frame)
     }
 }
+
+
+/// Provide a default implementation of `defaultHeaderFooterProperties` which returns an
+/// empty instance that does not provide any defaults.
+public extension HeaderFooterContent
+{
+    var defaultHeaderFooterProperties : DefaultProperties {
+        .init()
+    }
+}

ListableUI/Sources/Item/Item.swift

@@ -77,44 +77,14 @@ public struct Item<Content:ItemContent> : AnyItem
         assertIsValueType(Content.self)
 
         self.content = content
-
-        if let sizing = sizing {
-            self.sizing = sizing
-        } else if let sizing = content.defaultItemProperties.sizing {
-            self.sizing = sizing
-        } else {
-            self.sizing = .thatFits(.init(.atLeast(.default)))
-        }
 
-        if let layouts = layouts {
-            self.layouts = layouts
-        } else if let layouts = content.defaultItemProperties.layouts {
-            self.layouts = layouts
-        } else {
-            self.layouts = ItemLayouts()
-        }
+        let defaults = self.content.defaultItemProperties
 
-        if let selectionStyle = selectionStyle {
-            self.selectionStyle = selectionStyle
-        } else if let selectionStyle = content.defaultItemProperties.selectionStyle {
-            self.selectionStyle = selectionStyle
-        } else {
-            self.selectionStyle = .notSelectable
-        }
-
-        if let insertAndRemoveAnimations = insertAndRemoveAnimations {
-            self.insertAndRemoveAnimations = insertAndRemoveAnimations
-        } else if let insertAndRemoveAnimations = content.defaultItemProperties.insertAndRemoveAnimations {
-            self.insertAndRemoveAnimations = insertAndRemoveAnimations
-        }
-
-        if let swipeActions = swipeActions {
-            self.swipeActions = swipeActions
-        } else if let swipeActions = content.defaultItemProperties.swipeActions {
-            self.swipeActions = swipeActions
-        } else {
-            self.swipeActions = nil
-        }
+        self.sizing = finalValue(from: sizing, defaults.sizing, .thatFits(.init(.atLeast(.default))))
+        self.layouts = finalValue(from: layouts, defaults.layouts, .init())
+        self.selectionStyle = finalValue(from: selectionStyle, defaults.selectionStyle, .notSelectable)
+        self.insertAndRemoveAnimations = finalValue(from: insertAndRemoveAnimations, defaults.insertAndRemoveAnimations, nil)
+        self.swipeActions = finalValue(from: swipeActions, defaults.swipeActions, nil)
 
         self.reordering = reordering
         self.onWasReordered = onWasReordered
@@ -203,3 +173,19 @@ extension Item : SignpostLoggable
         )
     }
 }
+
+
+private func finalValue<Value>(
+    from provided : Value?,
+    _ contentDefault : Value?,
+    _ default : @autoclosure () -> Value
+) -> Value
+{
+    if let value = provided {
+        return value
+    } else if let value = contentDefault {
+        return value
+    } else {
+        return `default`()
+    }
+}

ListableUI/Sources/Item/ItemContent.swift

@@ -315,9 +315,12 @@ public protocol ItemContent where Coordinator.ItemContentType == Self
     // MARK: Default Item Properties
     //
 
+    typealias DefaultProperties = DefaultItemProperties<Self>
+
+
     /// Default values to assign to various properties on the `Item` which wraps
     /// this `ItemContent`, if those values are not passed to the `Item` initializer.
-    var defaultItemProperties : DefaultItemProperties<Self> { get }
+    var defaultItemProperties : DefaultProperties { get }
 
     //
     // MARK: Applying To Displayed View
@@ -539,7 +542,7 @@ public extension ItemContent
 /// empty instance that does not provide any defaults.
 public extension ItemContent
 {
-    var defaultItemProperties : DefaultItemProperties<Self> {
+    var defaultItemProperties : DefaultProperties {
         .init()
     }
 }