Swift And Painless

Aug 12, 2014
iOS 8 Share Extension With A Shared Keychain

Extensions are one of the coolest new features in iOS8. Nearly every iOS developer (and user) has waited for this for a long time. Finally very [convenient scenarios](http://oleb.net/blog/2014/06/the-power-of-ios8/) come true. In fact [AgileBits](http://agilebits.com/) (creator of 1Password) has already [published](https://github.com/AgileBits/onepassword-app-extension) a class to integrate 1Password extension support into every App. This is really cool.

Now let's say we want to build a share extension for a social networking App. To post to the social network the user has to be logged in (usually this means the user needs a valid access token). We don't want to force the user to log into the network twice. We want to share the access token between the App and the extension. How can we do this?

One possibility is to use a shared user defaults. But in this case the access token would be stored unencrypted on the device. This is not a good idea.

What we need is to store the access token in the keychain of iOS and access this keychain from the App and the extension. Let's do exactly this. (The demo project is on [github](https://github.com/dasdom/KeychainDemo).)

> As far as I understand it, I'm not allowed to show screenshots from Xcode 6 and iOS8 because those are still under NDA. I will update this post with screenshots when the NDA is lifted.

Open Xcode6 and create a new project. Select the Single View Application template. Chose a name, select the language Swift and select iPhone as the target device.

We need to access the keychain in the App and in the extension. Therefore the code to do that needs to be accessible from both targets. This is the perfect use case for a framework.
In the project navigator select the project. Add a new target to the project and make it framework. Chose the name KeychainAccess. Let the 'Project' and the 'Embed in Application' as it is.

In the project navigator navigate to the folder KeychainAccess. Add a file to this folder. Select an iOS-Swift file and name it KeychainAccess.swift. Replace the content of the file with this:
```
import Foundation

public class DDHKeychain {
    
    private class func secClassGenericPassword() -> String {
        return NSString(format: kSecClassGenericPassword)
    }
    
    private class func secClass() -> String {
        return NSString(format: kSecClass)
    }
    
    private class func secAttrService() -> String {
        return NSString(format: kSecAttrService)
    }
    
    private class func secAttrAccount() -> String {
        return NSString(format: kSecAttrAccount)
    }
    
    private class func secValueData() -> String {
        return NSString(format: kSecValueData)
    }
    
    private class func secReturnData() -> String {
        return NSString(format: kSecReturnData)
    }

    
    public class func setPassword(password: String, account: String, service: String = "kDDHDefaultService") {
        var secret: NSData = password.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)!
        let objects: Array = [secClassGenericPassword(), service, account, secret]
        
        let keys: Array = [secClass(), secAttrService(), secAttrAccount(), secValueData()]
        
        let query = NSDictionary(objects: objects, forKeys: keys)
        
        SecItemDelete(query as CFDictionaryRef)
        
        let status = SecItemAdd(query as CFDictionaryRef, nil)
    }
    
    public class func passwordForAccount(account: String, service: String = "kDDHDefaultService") -> String {
        
        let queryAttributes = NSDictionary(objects: [secClassGenericPassword(), service, account, true], forKeys: [secClass(), secAttrService(), secAttrAccount(), secReturnData()])
        
        
        var dataTypeRef : Unmanaged<AnyObject>?
        let status = SecItemCopyMatching(queryAttributes, &dataTypeRef);
        
        let retrievedData : NSData = dataTypeRef!.takeRetainedValue() as NSData
        
        let password = NSString(data: retrievedData, encoding: NSUTF8StringEncoding)
        
        return password as String
    }
    
}
```
This is basic keychain access. Please don't use this in production code. This is just for demo purposes. (As a bare minimum this class needed some error handling. But for the demo this is just enough.)

To add an extension to the project, add another target. Make it a share extension and call it `LinkShare`. Again 'Project' should be your project and 'Embed in Application' should be your application. If Xcode asks you whether it should activate a "LinkShare" scheme, select Activate.

To share a keychain between the application and it's embedded extension both have to have keychain sharing activated.
Select your App target and open the 'Capabilities' tab. Activate Keychain Sharing. Now select the LinkShare target and activate Keychain Sharing as well. In the LinkShare target add a keychain group and give it the same identifier as the keychain group in the main target. Delete the other keychain group. Now both targets share the same keychain.

In the LinkShare target in the 'General' tab link against the KeychainAccess.framework.

Now open the 'Info' tab of the LinkShare target and navigate to
NSExtension > NSExtensionAttributes > NSExtensionActivationRule
. Change the NSExtensionActivationSupportsWebURLWithMaxCount to 1.

In this demo we want to type a "password" in the application and we want to read it in the extension. (In a real application we would log into an API and receive an access token. This would then be stored in the shared keychain and accessed from both, the application and the extension.)

Open the main storyboard of the application target and ad a textfield. Add constraints. Make the View Controller the delegate of the textfield. Replace the code in `ViewController.swift` with:
```
import UIKit
import KeychainAccess

class ViewController: UIViewController, UITextFieldDelegate {
    
    func textFieldShouldReturn(textField: UITextField!) -> Bool {
        KeychainAccess.setPassword(textField.text, account: "SharedAccount")
        textField.resignFirstResponder()
        return false
    }
    
}
```
In the folder of the share extension open the file `ShareViewController.swift`. Import the KeychainAccess module ( import KeychainAccess ) and add the function:
```
override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)
        
        let password = KeychainAccess.passwordForAccount("SharedAccount")
        textView.text = password
    }
```
Now, build and run with the application scheme. Enter a password in the textfield. Then open a website in Safari and select the share button. In the popup select more and activate the LinkShare extension. Select the LinkShare extension.

You should now see the password you have entered in the textfield of the application.

It's magic, isn't it?

**Update:** Updated for Xcode 6.1 and Swift 1.1.
Read more...

Aug 4, 2014

Array Extensions

Useful array extensions. I'll update when I have more.

extension Array {
    func indexOf<T: Equatable>(obj: T) -> Int? {
        var foundIndex: Int? = nil
        for (index, element) in enumerate(self) {
            if element as? T == obj {
                foundIndex = index
                break
            }
        }
        return foundIndex
    }
}

extension Array {
    func contains<T : Equatable>(obj: T) -> Bool {
        return self.filter({$0 as? T == obj}).count > 0
    }
}

Ultralight View Controllers without Interface Builder

Since I read the [first issue of objc.io](http://www.objc.io/issue-1/) I try to make my view controllers as light weight as possible.

A month ago [Chris Eidhof](https://twitter.com/chriseidhof) wrote a [great blogpost](http://chris.eidhof.nl/posts/intentions.html) about his experiment with Ultralight View Controllers using [Intentions](http://bendyworks.com/geekville/articles/2014/2/single-responsibility-principle-ios). Chris uses a storyboard and adds a model container and intentions to it.

Personally I don't like the Interface Builder and avoid it when ever I can. To understand what Chris did and to decide whether I like it I had to change [the example code](https://github.com/chriseidhof/intentions) and get rid of the Interface Builder. You can download the project from [github](https://github.com/dasdom/intentions).

> **tl;dr**: I first tired to but everything what was in the storyboard into a view class. But this resulted in a bloated init method for the view. I then realized that the view controller should be responsible for connecting all the intentions and hold a reverence to the model container.

###AppDelegate

Without a storyboard we have to create the window and make it key. And we have to define the rootViewController of the window.

#import "AppDelegate.h"
#import "ViewController.h"

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application 
        didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

    ViewController *viewController = [[ViewController alloc] init];
    self.window.rootViewController = viewController;
    
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;
}

@end

Nothing magical here.

##First Try

###View

As the storyboard is gone we need a class for the view. In Chris' example the storyboard scene for the view controller included all the needed intentions and the model container. The intentions react on changes in the user interface. Therefore in this example I'll put them into the view class. I'm not really happy with this approach but I think this is comparable to putting them into the scene of the view controller in the storyboard. (Is this true? Is this comparable? Should they be in a separate class and be connected in the view controller? Let me know what you think.)

//  View.h

#import <UIKit/UIKit.h>
#import "ModelContainer.h"

@interface View : UIView
@property (nonatomic, strong) ModelContainer *modelContainer;
@end

In the implementation we fist have to create the model container and than add all the UI elements which have been in the storyboard.

@implementation View

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // ModelContainer
        _modelContainer = [[ModelContainer alloc] init];
        
        // UI
        _textField = [[UITextField alloc] init];
        _textField.translatesAutoresizingMaskIntoConstraints = NO;
        _textField.borderStyle = UITextBorderStyleRoundedRect;
        [self addSubview:_textField];
        
        _reverseButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
        _reverseButton.translatesAutoresizingMaskIntoConstraints = NO;
        [_reverseButton setTitle:@"Reverse" forState:UIControlStateNormal];
        [self addSubview:_reverseButton];
        
        _uppercaseButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
        _uppercaseButton.translatesAutoresizingMaskIntoConstraints = NO;
        [_uppercaseButton setTitle:@"Uppercase" forState:UIControlStateNormal];
        [self addSubview:_uppercaseButton];
        
        _label = [[UILabel alloc] init];
        _label.translatesAutoresizingMaskIntoConstraints = NO;
        _label.text = @"Label";
        [self addSubview:_label];
        
        NSDictionary *viewsDictionary = NSDictionaryOfVariableBindings(_textField, _reverseButton, 
                                                                       _uppercaseButton, _label);
        [self addConstraints:[NSLayoutConstraint 
                              constraintsWithVisualFormat:@"|-20-[_textField(==_label)]-20-|" 
                                                  options:kNilOptions 
                                                  metrics:nil 
                                                    views:viewsDictionary]];
        
        [self addConstraints:[NSLayoutConstraint 
                              constraintsWithVisualFormat:@"V:|-40-[_textField]-20-[_reverseButton(40)]-20-[_label(==30)]" 
                                                  options:NSLayoutFormatAlignAllLeft 
                                                  metrics:nil 
                                                    views:viewsDictionary]];

        [self addConstraints:[NSLayoutConstraint 
                              constraintsWithVisualFormat:@"V:[_textField]-20-[_uppercaseButton(==_reverseButton)]" 
                                                  options:NSLayoutFormatAlignAllRight 
                                                  metrics:nil 
                                                    views:viewsDictionary]];

Now we need all the intentions. I have added init methods to the intentions to make the connections which have previously been made in the storyboard.


        // Intentions
        _reverseIntention = [[ReverseIntention alloc] initWithModelContainer:_modelContainer 
                                                                modelKeyPath:@"name" 
                                                                   textField:_textField];

        _uppercaseIntention = [[UppercaseIntention alloc] initWithModelContainer:_modelContainer 
                                                                    modelKeyPath:@"name" 
                                                                       textField:_textField];

        _dismissOnEnterIntention = [[DismissOnEnterIntention alloc] init];
       
        _observeIntentionForTextField = [[ObserveIntention alloc] initWithSource:_modelContainer 
                                                                   sourceKeyPath:@"model.name" 
                                                                          target:_textField 
                                                                   targetKeyPath:@"text"];

        _observeIntentionForLabel = [[ObserveIntention alloc] initWithSource:_modelContainer 
                                                               sourceKeyPath:@"model.name" 
                                                                      target:_label 
                                                               targetKeyPath:@"text"];
        
        [_reverseButton addTarget:_reverseIntention 
                           action:@selector(reverse) 
                 forControlEvents:UIControlEventTouchUpInside];

        [_uppercaseButton addTarget:_uppercaseIntention 
                             action:@selector(capitalize) 
                   forControlEvents:UIControlEventTouchUpInside];
        
        _textField.delegate = _dismissOnEnterIntention;
    }
    return self;
}

@end

###ViewController

The view controller has to create a view and assign it to self.view in loadView. I have moved the creation of the person instance and the assignment to the model controller also into loadView. We could leave it in viewDidLoad but then we needed two methods in the view controller instead of one which I think would result in more weight.

#import "ViewController.h"
#import "ModelContainer.h"
#import "Person.h"
#import "View.h"

@interface ViewController ()

@property (strong, nonatomic) ModelContainer* modelContainer;

@end

@implementation ViewController

- (void)loadView {
    View *contentView = [[View alloc] init];

    self.modelContainer = contentView.modelContainer;
    
    Person *person = [Person new];
    person.name = @"Dominik";
    self.modelContainer.model = person;
    
    self.view = contentView;
}

@end

###Code smell

In this example the cost for the ultralight view controller is a kind of heavy view class. Especially the model container in the view bothers me. We could get rid of the model container in the view by creating it in the loadView method of the view controller. But in this case the init method of the view should have it as a parameter because we need to make the connections to the intentions.

Discussing this example I realized that I have no idea how the Interface Builder fits into the Model View Controller pattern. Do the objects added to a scene in the storyboard belong to the view or to the view controller? Maybe both... So this is more like Model-View-ViewModel without the ViewModel.

(I not even sure if my approach is comparable to what Chris did in the storyboard.)

##Second Try

Seeing the code in one place this seems wrong to me. I think the intentions should be properties of the view controller. They should be created in viewDidLoad and connected to the UI elements of the view.

So the view controller implementation would look like this:

//
//  ViewController2.m
//  Intentions
//
//  Created by Dominik Hauser on 23.05.14.
//  Copyright (c) 2014 Dominik Hauser. All rights reserved.
//

#import "ViewController2.h"
#import "ModelContainer.h"
#import "Person.h"
#import "View2.h"

#import "ReverseIntention.h"
#import "UppercaseIntention.h"
#import "DismissOnEnterIntention.h"
#import "ObserveIntention.h"

@interface ViewController2 ()
@property (strong, nonatomic) ModelContainer* modelContainer;

@property (nonatomic, strong) ReverseIntention *reverseIntention;
@property (nonatomic, strong) UppercaseIntention *uppercaseIntention;
@property (nonatomic, strong) DismissOnEnterIntention *dismissOnEnterIntention;
@property (nonatomic, strong) ObserveIntention *observeIntentionForTextField;
@property (nonatomic, strong) ObserveIntention *observeIntentionForLabel;
@end

@implementation ViewController2

- (instancetype)init {
    self = [super init];
    if (self) {
        _modelContainer = [[ModelContainer alloc] init];
    }
    return self;
}

- (void)loadView {
    View2 *contentView = [[View2 alloc] init];
    
    Person *person = [Person new];
    person.name = @"Dominik";
    self.modelContainer.model = person;
    
    self.view = contentView;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    self.reverseIntention = [[ReverseIntention alloc] initWithModelContainer:self.modelContainer modelKeyPath:@"name" textField:((View2*)self.view).textField];
    _uppercaseIntention = [[UppercaseIntention alloc] initWithModelContainer:_modelContainer modelKeyPath:@"name" textField:((View2*)self.view).textField];
    _dismissOnEnterIntention = [[DismissOnEnterIntention alloc] init];
    _observeIntentionForTextField = [[ObserveIntention alloc] initWithSource:_modelContainer sourceKeyPath:@"model.name" target:((View2*)self.view).textField targetKeyPath:@"text"];
    _observeIntentionForLabel = [[ObserveIntention alloc] initWithSource:_modelContainer sourceKeyPath:@"model.name" target:((View2*)self.view).label targetKeyPath:@"text"];
    
    [((View2*)self.view).reverseButton addTarget:_reverseIntention action:@selector(reverse) forControlEvents:UIControlEventTouchUpInside];
    [((View2*)self.view).uppercaseButton addTarget:_uppercaseIntention action:@selector(capitalize) forControlEvents:UIControlEventTouchUpInside];
    ((View2*)self.view).textField.delegate = _dismissOnEnterIntention;
}

And the view would become:

//
//  View2.m
//  Intentions
//
//  Created by Dominik Hauser on 23.05.14.
//  Copyright (c) 2014 Dominik Hauser. All rights reserved.
//

#import "View2.h"

@implementation View2

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = [UIColor lightGrayColor];
        
        // UI
        _textField = [[UITextField alloc] init];
        _textField.translatesAutoresizingMaskIntoConstraints = NO;
        _textField.borderStyle = UITextBorderStyleRoundedRect;
        [self addSubview:_textField];
        
        _reverseButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
        _reverseButton.translatesAutoresizingMaskIntoConstraints = NO;
        [_reverseButton setTitle:@"Reverse" forState:UIControlStateNormal];
        [self addSubview:_reverseButton];
        
        _uppercaseButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
        _uppercaseButton.translatesAutoresizingMaskIntoConstraints = NO;
        [_uppercaseButton setTitle:@"Uppercase" forState:UIControlStateNormal];
        [self addSubview:_uppercaseButton];
        
        _label = [[UILabel alloc] init];
        _label.translatesAutoresizingMaskIntoConstraints = NO;
        _label.text = @"Label";
        [self addSubview:_label];
        
        NSDictionary *viewsDictionary = NSDictionaryOfVariableBindings(_textField, _reverseButton, _uppercaseButton, _label);
        [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"|-20-[_textField(==_label)]-20-|" options:kNilOptions metrics:nil views:viewsDictionary]];
        
        [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-40-[_textField]-20-[_reverseButton(40)]-20-[_label(==30)]" options:NSLayoutFormatAlignAllLeft metrics:nil views:viewsDictionary]];
        
        [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[_textField]-20-[_uppercaseButton(==_reverseButton)]" options:NSLayoutFormatAlignAllRight metrics:nil views:viewsDictionary]];
    }
    return self;
}

@end

This looks much better than my first approach. But the view controller isn't ultra light anymore. I would still call it a light view controller but there seems to be potential to reduce it further. I'll think about it.

**Update:** For fun I have rewritten the Intentions example in Swift. [Check it out.](https://github.com/dasdom/IntentionsWithSwift)

In case you have any comments about this you can find me on [App.net](https://alpha.app.net/dasdom) and on [Twitter](https://twitter.com/dasdom).

Coloring parentheses in a calculation string

Right now I am working on an update for [Phy](https://itunes.apple.com/de/app/phy-physics-formulas-calculator/id325836855?l=en&mt=8).

One of the things which had to be improved was calculation string in the calculator. As a physicist I often had the problem that is was difficult to keep an overview of all the opening and closing parenthesis. One solution could be to use different types of parenthesis. But this is something I don't like ascetically. Even when I write formulas on paper I only use on pair of parenthesis.

Another solution could be to use different colors for different pairs of parenthesis. The only problem in the implementation of this solution is, that the parentheses can be nested. So in the example `(1+(2+3))`. The first opening and the last closing parentheses should have the same color and it should be different from the color of the second opening and the first closing parentheses.

Here is what I wanted to accomplish for a more complicated example:

I solved this problem by iterating through the string and find the first closing parenthesis. On the way I stored the location of all the opening parentheses in an array. Then, when the first closing parenthesis was found, I have just look for the last opening parenthesis which was stored. This was then removed from the array and a range from the opening to the closing parenthesis is added to another array. This sounds quite complicated but in fact is very easy to do. This is the code I use to create an attributed string to color all pairs of parentheses and the calculation signs. In addition all unmatched opening parentheses are colored in red.

- (NSAttributedString*)coloredAttributedStringFromString:(NSString*)string {
    
    NSMutableArray *openArray = [NSMutableArray array];
    
    NSMutableArray *parenthesesPairsArray = [NSMutableArray array];
    NSMutableArray *calcSignsRanges = [NSMutableArray array];
    
    if (self.calculationSigns) {
        self.calculationSigns = @[@"/", @"⨯", @"−", @"+"];
    }
    if (!self.openingParenthesis) {
        self.openingParenthesis = @"(";
    }
    if (!self.closingParenthesis) {
        self.closingParenthesis = @")";
    }

    [string enumerateSubstringsInRange:NSMakeRange(0, string.length)
                               options:NSStringEnumerationByComposedCharacterSequences
                            usingBlock:^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop) {
        
        if ([self.calculationSigns containsObject:substring]) {
            [calcSignsRanges addObject:[NSValue valueWithRange:substringRange]];
        } else if ([substring isEqualToString:self.openingParenthesis]) {
            [openArray addObject:[NSValue valueWithRange:substringRange]];
        } else if ([substring isEqualToString:self.closingParenthesis]) {
            NSValue *openValue = [openArray lastObject];
            NSRange parenthesesRange;
            if (openValue) {
                NSRange openRange = [[openArray lastObject] rangeValue];
                NSInteger length = substringRange.location-openRange.location;
                if (length < 1) {
                    length = 1;
                }
                parenthesesRange = NSMakeRange(openRange.location, length);
                [parenthesesPairsArray addObject:[NSValue valueWithRange:parenthesesRange]];
                [openArray removeLastObject];
            }
        }
    }];
    
    NSMutableAttributedString *attributedString = [[NSMutableAttributedString alloc] initWithString:string];

    [openArray enumerateObjectsUsingBlock:^(NSValue *rangeValue, NSUInteger idx, BOOL *stop) {
        NSRange range = [rangeValue rangeValue];
        [attributedString addAttribute:NSForegroundColorAttributeName value:(self.unPairedParenthesisColor ?: [UIColor redColor]) range:range];
    }];
    
    NSInteger numberOfColors = [self.parenthesesColors count];
    [parenthesesPairsArray enumerateObjectsUsingBlock:^(NSValue *rangeValue, NSUInteger idx, BOOL *stop) {
        UIColor *color = self.parenthesesColors[idx % numberOfColors];
        NSRange parenthesesRange = [rangeValue rangeValue];
        NSRange range = NSMakeRange(parenthesesRange.location, 1);
        [attributedString addAttribute:NSForegroundColorAttributeName value:color range:range];
        range = NSMakeRange(parenthesesRange.location+parenthesesRange.length, 1);
        [attributedString addAttribute:NSForegroundColorAttributeName value:color range:range];
    }];
    
    [calcSignsRanges enumerateObjectsUsingBlock:^(NSValue *rangeValue, NSUInteger idx, BOOL *stop) {
        UIColor *defaultCalcSignColor = [UIColor colorWithRed:0.000 green:0.251 blue:0.502 alpha:1.000];
        NSRange range = [rangeValue rangeValue];
        [attributedString addAttribute:NSForegroundColorAttributeName value:(self.calculationSignsColor ?: defaultCalcSignColor) range:range];
    }];
    
    [attributedString addAttribute:NSFontAttributeName value:[UIFont fontWithName:@"Menlo" size:13.0f] range:NSMakeRange(0, attributedString.length)];

    return attributedString;
}

iOS 8 Share Extension With A Shared Keychain

Array Extensions

A Closure To Define Buttons

Table View Cells in iOS8

Storyboards and Xibs

Ultralight View Controllers without Interface Builder

Coloring parentheses in a calculation string

Custom view controller transitions with UIDynamic behaviors

My reasons not to use AppCode

Code generator for property existence unit tests