Introduce CacheClearer to force clear static caches

CacheClearer.swift

@@ -0,0 +1,19 @@
+import Foundation
+
+@_spi(CacheManagement)
+public struct CacheClearer {
+
+    /// Clears all static caches that are in use.
+    ///
+    /// Listable leverages static caching to improve performance however there are situations in which
+    /// this can cause object lifetimes to be extended unexpectedly, especially in cases where cached
+    /// views reference other objects.
+    ///
+    /// - WARNING: Clearing these caches can have global performance implications. This method
+    /// should be invoked sparingley and only after other workarounds to manage object lifetimes have failed.
+    @_spi(CacheManagement)
+    public static func clearStaticCaches() {
+        ListProperties.headerFooterMeasurementCache.removeAllObjects()
+        ListProperties.itemMeasurementCache.removeAllObjects()
+    }
+}

CacheClearerTests.swift

@@ -0,0 +1,19 @@
+import XCTest
+@testable @_spi(CacheManagement) import ListableUI
+
+class CacheClearerTests: XCTestCase {
+
+    func test_clearStaticCaches() {
+
+        ListProperties.headerFooterMeasurementCache.push(UIView(), with: .identifier(for: UIView.self))
+        ListProperties.itemMeasurementCache.push(UIView(), with: .identifier(for: UIView.self))
+
+        XCTAssertEqual(ListProperties.headerFooterMeasurementCache.cachedViewCount, 1)
+        XCTAssertEqual(ListProperties.itemMeasurementCache.cachedViewCount, 1)
+
+        CacheClearer.clearStaticCaches()
+
+        XCTAssertEqual(ListProperties.headerFooterMeasurementCache.cachedViewCount, 0)
+        XCTAssertEqual(ListProperties.itemMeasurementCache.cachedViewCount, 0)
+    }
+}

ListableUI/Sources/Internal/ReusableViewCache.swift

@@ -11,7 +11,11 @@ import Foundation
 final class ReusableViewCache
 {
     private var views : [String:[AnyObject]] = [:]
-
+
+    var cachedViewCount : Int {
+        return self.views.values.reduce(0) { $0 + $1.count }
+    }
+
     init() {}
 
     func count<Content>(for reuseIdentifier : ReuseIdentifier<Content>) -> Int
@@ -61,4 +65,8 @@ final class ReusableViewCache
             return result
         }
     }
+
+    func removeAllObjects() {
+        self.views = [:]
+    }
 }

ListableUI/Sources/Layout/ListLayout/ListLayout+Layout.swift

@@ -11,8 +11,8 @@ import UIKit
 
 extension ListProperties {
 
-    private static let headerFooterMeasurementCache = ReusableViewCache()
-    private static let itemMeasurementCache = ReusableViewCache()
+    static let headerFooterMeasurementCache = ReusableViewCache()
+    static let itemMeasurementCache = ReusableViewCache()
 
     /// **Note**: For testing or measuring content sizes only.
     ///

ListableUI/Tests/Internal/ReusableViewCacheTests.swift

@@ -168,6 +168,36 @@ class ReusableViewCacheTests: XCTestCase
             XCTAssertEqual(result, "result")
         }
     }
+
+    func test_removeAllObjects() {
+        self.testcase("empty") {
+            let cache = ReusableViewCache()
+
+            XCTAssertEqual(cache.cachedViewCount, 0)
+
+            cache.removeAllObjects()
+
+            XCTAssertEqual(cache.cachedViewCount, 0)
+        }
+
+        self.testcase("non-empty") {
+            let cache = ReusableViewCache()
+
+            let view1 = TestView1()
+            view1.identifier = "pushed_1"
+            cache.push(view1, with: ReuseIdentifier.identifier(for: TestView1.self))
+
+            let view2 = TestView1()
+            view2.identifier = "pushed_2"
+            cache.push(view2, with: ReuseIdentifier.identifier(for: TestView1.self))
+
+            XCTAssertEqual(cache.cachedViewCount, 2)
+
+            cache.removeAllObjects()
+
+            XCTAssertEqual(cache.cachedViewCount, 0)
+        }
+    }
 }