[iOS] Show activity indicator during generation

iOS/Base.lproj/Main.storyboard

@@ -462,5 +462,40 @@
             </objects>
             <point key="canvasLocation" x="1993" y="-423"/>
         </scene>
+        <!--View Controller-->
+        <scene sceneID="8JA-Zd-1zR">
+            <objects>
+                <viewController storyboardIdentifier="activityIndicator" id="asG-zz-a8o" sceneMemberID="viewController">
+                    <layoutGuides>
+                        <viewControllerLayoutGuide type="top" id="hu7-uJ-ly6"/>
+                        <viewControllerLayoutGuide type="bottom" id="vvJ-kn-Vjf"/>
+                    </layoutGuides>
+                    <view key="view" alpha="0.90000000000000002" contentMode="scaleToFill" id="c3D-Ze-5hZ">
+                        <rect key="frame" x="0.0" y="0.0" width="375" height="667"/>
+                        <autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>
+                        <subviews>
+                            <activityIndicatorView opaque="NO" contentMode="scaleToFill" horizontalHuggingPriority="750" verticalHuggingPriority="750" animating="YES" style="whiteLarge" translatesAutoresizingMaskIntoConstraints="NO" id="Qe7-Bk-J1n"/>
+                            <label opaque="NO" userInteractionEnabled="NO" contentMode="left" horizontalHuggingPriority="251" verticalHuggingPriority="251" text="Generating…" textAlignment="center" lineBreakMode="tailTruncation" baselineAdjustment="alignBaselines" adjustsFontSizeToFit="NO" translatesAutoresizingMaskIntoConstraints="NO" id="gXF-vs-Gda">
+                                <constraints>
+                                    <constraint firstAttribute="width" constant="101" id="jwK-5C-D2D"/>
+                                </constraints>
+                                <fontDescription key="fontDescription" type="system" pointSize="17"/>
+                                <color key="textColor" white="1" alpha="1" colorSpace="calibratedWhite"/>
+                                <nil key="highlightedColor"/>
+                            </label>
+                        </subviews>
+                        <color key="backgroundColor" cocoaTouchSystemColor="darkTextColor"/>
+                        <constraints>
+                            <constraint firstItem="Qe7-Bk-J1n" firstAttribute="centerY" secondItem="c3D-Ze-5hZ" secondAttribute="centerY" id="9Lb-iu-cD0"/>
+                            <constraint firstItem="Qe7-Bk-J1n" firstAttribute="centerX" secondItem="c3D-Ze-5hZ" secondAttribute="centerX" id="DYg-1r-kfn"/>
+                            <constraint firstItem="Qe7-Bk-J1n" firstAttribute="centerX" secondItem="gXF-vs-Gda" secondAttribute="centerX" id="d15-94-nf5"/>
+                            <constraint firstItem="gXF-vs-Gda" firstAttribute="top" secondItem="Qe7-Bk-J1n" secondAttribute="bottom" constant="8" symbolic="YES" id="n3a-cK-5jh"/>
+                        </constraints>
+                    </view>
+                </viewController>
+                <placeholder placeholderIdentifier="IBFirstResponder" id="VFj-Pa-4qu" userLabel="First Responder" sceneMemberID="firstResponder"/>
+            </objects>
+            <point key="canvasLocation" x="2896.8000000000002" y="-423.23838080959524"/>
+        </scene>
     </scenes>
 </document>

iOS/ShowDetailsController.m

@@ -31,7 +31,7 @@
 #import "LegacyPasswordGenerator.h"
 
 @interface ShowDetailsController ()
-- (NSMutableString*)_generate;
+- (void)_generateWithCallback: (void(^)(NSMutableString*))block;
 - (void)_generateAndCopy;
 - (void)_generateAndShow;
 @end
@@ -113,8 +113,7 @@ clearNSMutableString(NSMutableString *string)
 
 - (void)_generateAndCopy
 {
-	NSMutableString *password = [self _generate];
+	[self _generateWithCallback: ^ (NSMutableString *password) {
-
 		UIPasteboard *pasteBoard = [UIPasteboard generalPasteboard];
 		pasteBoard.string = password;
 
@@ -122,8 +121,8 @@ clearNSMutableString(NSMutableString *string)
 
 		UIAlertController *alert = [UIAlertController
 		    alertControllerWithTitle: @"Password Generated"
-			     message: @"The password has been copied into the "
+				     message: @"The password has been copied "
-				      @"clipboard."
+					      @"into the clipboard."
 			      preferredStyle: UIAlertControllerStyleAlert];
 		[alert addAction:
 		    [UIAlertAction actionWithTitle: @"OK"
@@ -135,12 +134,12 @@ clearNSMutableString(NSMutableString *string)
 		[self presentViewController: alert
 				   animated: YES
 				 completion: nil];
+	}];
 }
 
 - (void)_generateAndShow
 {
-	NSMutableString *password = [self _generate];
+	[self _generateWithCallback: ^ (NSMutableString *password) {
-
 		UIAlertController *alert = [UIAlertController
 		    alertControllerWithTitle: @"Generated Passphrase"
 				     message: password
@@ -149,7 +148,8 @@ clearNSMutableString(NSMutableString *string)
 		    [UIAlertAction actionWithTitle: @"OK"
 					     style: UIAlertActionStyleDefault
 					   handler: ^ (UIAlertAction *action) {
-		[self.navigationController popViewControllerAnimated: YES];
+			[self.navigationController
+			    popViewControllerAnimated: YES];
 		}]];
 
 		[self presentViewController: alert
@@ -157,10 +157,20 @@ clearNSMutableString(NSMutableString *string)
 				 completion: ^ {
 			clearNSMutableString(password);
 		}];
+	}];
 }
 
-- (NSMutableString*)_generate
+- (void)_generateWithCallback: (void(^)(NSMutableString*))block
 {
+	UIStoryboard *mainStoryboard =
+	[UIStoryboard storyboardWithName: @"Main"
+				  bundle: nil];
+	UIViewController *activityController = [mainStoryboard
+	    instantiateViewControllerWithIdentifier: @"activityIndicator"];
+	[self.navigationController.view addSubview: activityController.view];
+
+	dispatch_async(dispatch_get_global_queue(
+	    DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {
 		id <PasswordGenerator> generator;
 		char *passphrase;
 
@@ -188,7 +198,9 @@ clearNSMutableString(NSMutableString *string)
 		of_explicit_memset(generator.output, 0,
 		    strlen((char*)generator.output));
 
-	return password;
+		activityController.view.hidden = YES;
+		block(password);
+	});
 }
 
 - (IBAction)remove: (id)sender