minor tweaks: expansion of memory management example, clarification o…

…f popover adaptation

bk2ch06p336memoryWarning/ch19p647memoryWarning/ViewController.swift

@@ -4,6 +4,41 @@ import Foundation
 
 class ViewController : UIViewController {
 
+    // ignore; just making sure it compiles
+
+
+    let cache = NSCache()
+    var cachedData : NSData {
+        let key = "somekey"
+        var data = self.cache.objectForKey(key) as? NSData
+        if data != nil {
+            return data!
+        }
+        // ... recreate data here ...
+        data = NSData() // recreated data
+        self.cache.setObject(data!, forKey: key)
+        return data!
+    }
+
+    var purgeable = NSPurgeableData()
+    var purgeabledata : NSData {
+        // surprisingly tricky to get content access barriers correct
+        if self.purgeable.beginContentAccess() && self.purgeable.length > 0 {
+            let result = self.purgeable.copy() as! NSData
+            self.purgeable.endContentAccess()
+            return result
+        } else {
+            // ... recreate data here ...
+            let data = NSData() // recreated data
+            self.purgeable = NSPurgeableData(data:data)
+            self.purgeable.endContentAccess() // must call "end"!
+            return data
+        }
+    }
+
+
+    // this is the actual example
+
     private var myBigDataReal : NSData! = nil
     var myBigData : NSData! {
         set (newdata) {

bk2ch09p477popoversOnPhone/PopoverOnPhone/ViewController.swift

@@ -9,8 +9,8 @@ class ViewController: UIViewController {
         vc.preferredContentSize = CGSizeMake(400,500)
         vc.modalPresentationStyle = .Popover
 
-        // trick #1; declare the delegate _before_ presentation!
-        if let pres = vc.popoverPresentationController {
+        // declare the delegate _before_ presentation!
+        if let pres = vc.presentationController {
             pres.delegate = self // comment out to see what the defaults are
         }
 
@@ -45,11 +45,8 @@ class ViewController: UIViewController {
 extension ViewController : UIPopoverPresentationControllerDelegate {
 
     // UIPopoverPresentationControllerDelegate conforms to UIAdaptivePresentationControllerDelegate
-    // on iPhone, a popover is considered adaptive!
-    // therefore, the delegate is consulted
 
-    // trick #2: implement this method even if you want the default...
-    // NB I've switched to the newer method, so we are called on both iPad and iPhone
+    // no need to call this any longer, though you can if you want to
 
     func adaptivePresentationStyleForPresentationController(controller: UIPresentationController, traitCollection: UITraitCollection) -> UIModalPresentationStyle {
         if traitCollection.horizontalSizeClass == .Compact {
@@ -62,8 +59,6 @@ extension ViewController : UIPopoverPresentationControllerDelegate {
         return .None
     }
 
-    // trick #3: fix the interface for iPhone
-
     func presentationController(controller: UIPresentationController, viewControllerForAdaptivePresentationStyle style: UIModalPresentationStyle) -> UIViewController? {
         // we actually get the chance to swap out the v.c. for another!
         if style != .Popover {