Location Trivia - Data Store Relationships

Goals

Set up a shared data store using a singleton.
Use a shared instance to pass information between a group of view controllers.

Review

From time to time, we may want one instance of a class (and whatever data it holds onto) to be accessed by many other objects in your program. This is very useful for organizing your application's data into one place--hence the designation in this case of "Data Store." One way to accomplish this is with a shared instance of that class. A shared instance is typically accessed by a class method which creates only one instance over the lifetime of the application. Any and all calls to that class method return the one instance already instantiated. You'll often hear this referred to as a "singleton."

The dispatch_once function from Grand Central Dispatch (GCD) is what permits this behavior. It's kind of like a punch card that reads 'admit one.' It retains all of its identifying information, but won't permit the application to run the block argument more than once. In the current case, that means only instantiating the shared instance one time. The code that Apple provides for creating such a shared instance is this somewhat cryptic set of code:

+ (instancetype)shared<#name#> {
    static <#class#> *_shared<#name#> = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _shared<#name#> = <#initializer#>;
    });

    return _shared<#name#>;
}

In the scope of this lab we're going to call this class FISLocationsDataStore meaning we need to fill out the placeholders in this provided code as follows:

+ (instancetype)sharedLocationsDataStore {
    static FISLocationsDataStore *_sharedLocationsDataStore = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _sharedLocationsDataStore = [[FISLocationsDataStore alloc] init];
    });

    return _sharedLocationsDataStore;
}

You'll notice that it's calling a standard init on the class, so we'll need to customize that. Since we want our data store to hold our FISLocation objects, let's give it a property that's an NSMutableArray called 'locations' and instantiate it in the initializer.

// FISLocationsDataStore.h

@property (strong, nonatomic) NSMutableArray *locations;

// FISLocationsDataStore.m

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

Now that we have our singleton class set up, we can access it from any view controller by calling the shared<#name#> method that we previously set up.

- (void)viewDidLoad {
	[super viewDidLoad];
	
    FISLocationsDataStore *locationsDataStore = 
        [FISLocationsDataStore sharedLocationsDataStore];
}

This next lab already has these steps set up for you. Take a moment to look over the data store's files to see how they're laid out, then solve the lab by connecting a new view controller to the data store.

Instructions

The previously-used FISLocation and FISTrivium data models have been provided for you. Set up the FISLocationsDataStore class to be a singleton class. It should have one property, an NSMutableArray called locations. Override the default initializer to populate the locations array with the starting data provided at the end of this readme in the generateStartingLocationsData method.
Create a storyboard named Main.storyboard. Add a table view controller embedded in a navigation controller which is the initial view controller. This first table view controller should be connected to a class called FISLocationsTableViewController.

In viewDidLoad, set the tableView property's accessibility label & identifier to @"Locations Table" (this cannot be done in Interface Builder).
Give the table view controller a FISLocationsDataStore property called store and use the "shared instance" method to instantiate it.
In storyboard, set the table view's prototype cell type to "right detail". Have the table view use the textLabel to show the name of the locations, and the detailTextLabel to display the number of trivia it has associated with it.

Add a second table view controller named FISTriviaTableViewController accessed by a show segue from a table view cell in the locations table view controller. In viewDidLoad, set the tableView's accessibility label & identifier to @"Trivia Table".

Give the view controller a FISLocation property called location, which should be set with the relevant FISLocation object in FISLocationsTableViewController's prepareForSegue:sender: method.
Use the location property's trivia array to load the table view. Each cell should display the FISTrivium object's "content" in the textLabel, and the number of "likes" in the detailTextLabel.

Create a new view controller named FISAddLocationViewController that will be presented modally from the locations table view controller.

Add three text fields for the name, latitude, and longitude. Set their accessibility labels & identifiers to @"nameField", @"latitudeField, and @"longitudeField" respectively.
Add two buttons, one to "cancel" adding a location, and one to "save" a new location with the information entered in the text fields. Set their accessibility labels & identifiers to @"cancelButton" and @"saveButton" respectively.
When the "cancel" button is tapped, dismiss the view controller.
When the "submit" button is tapped, use the information in the text fields to create new a instance of FISLocation and add it the the data store's locations array. Then dismiss the view controller.

To access this new view controller, add a bar button item to the navigation bar in the location table view's storyboard canvas. Set the style to "add" so it shows a + sign. In the FISLocationsTableViewController's viewDidLoad method, set this new button's accessibility label & identifier to @"addButton". You can access it as a property via self.navigationItem.rightBarButtonItem and set the string properties from there.

Create a modal segue between this add button and the FISAddLocationViewController. Now that you have two segues, you'll need to detect which segue has been activated in the prepareForSegue: method — only one of the destination view controllers has a location property that can be set.

Use the iOS Simulator to test your add-location view controller. You may notice that the new location doesn't appear in the locations table view, even though the data has been added. How can you get the table view to reload itself?
Create another view controller named FISAddTriviaTableViewController to be presented modally from the the trivia table view controller. It will need one text field, a cancel button, and a save button. Set their accessibility labels & identifiers to @"Trivium Text Field", @"Cancel Button", and @"Save Button" respectively.

When the cancel button is tapped, dismiss the view controller.
When the submit button is tapped, add use the text field to create a new FISTrivium object with zero likes. Add the this new trivium to the relevant FISLocation object that was passed to the FISTriviaTableViewController. Then dismiss the view controller.

To access this last view controller, add a bar button to the navigation bar in the trivia table view's storyboard canvas. Set the style to "add" so it shows a + sign. In the FISTriviaTableViewController's viewDidLoad method, set this new button's accessibility label & identifier to @"Add Trivia Button". You can access this it as a property via self.navigationItem.rightBarButtonItem and set the string properties from there.

Create a modal segue between the add button and the FISAddTriviaViewController.

Use the iOS Simulator to test your add-trivia view controller. Does the new trivium show up in the FISTriviaTableViewController?

Starting Data

- (void)generateStartingLocationsData {
    FISLocation *empireState = [[FISLocation alloc] initWithName:@"The Empire State Building"
                                                        latitude:40.7484
                                                       longitude:-73.9857];
    
    FISTrivium *trivium1A = [[FISTrivium alloc] initWithContent:@"1,454 Feet Tall" likes:4];
    FISTrivium *trivium1B = [[FISTrivium alloc] initWithContent:@"Cost $24,718,000 to build" likes:2];
    
    [empireState.trivia addObjectsFromArray:@[trivium1A, trivium1B]];
    
    FISLocation *bowlingGreen = [[FISLocation alloc] initWithName:@"Bowling Green"
                                                         latitude:41.3739
                                                        longitude:-83.6508];
    
    FISTrivium *trivium2A = [[FISTrivium alloc] initWithContent:@"NYC's oldest park" likes:8];
    FISTrivium *trivium2B = [[FISTrivium alloc] initWithContent:@"Made a park in 1733" likes:2];
    FISTrivium *trivium2C = [[FISTrivium alloc] initWithContent:@"Charging Bull was created in 1989" likes:0];
    
    
    [bowlingGreen.trivia addObjectsFromArray:@[trivium2A, trivium2B, trivium2C]];
    
    FISLocation *ladyLiberty = [[FISLocation alloc] initWithName:@"Statue Of Liberty"
                                                        latitude:40.6892
                                                       longitude:74.0444];
    FISTrivium *trivium3A = [[FISTrivium alloc] initWithContent:@"Gift from the french" likes:6];
    
    [ladyLiberty.trivia addObjectsFromArray:@[trivium3A]];
    
    [self.locations addObjectsFromArray:@[bowlingGreen, empireState, ladyLiberty]];
}```

## Advanced

Add functionality to get the users actual location. Beware that significant changes to `CLLocation` were made with iOS 8, so resources older than September 2014 might be incorrect.

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colinfwalsh/locationTrivia-DataStoreRelationships-ios-0616

Location Trivia - Data Store Relationships

Goals

Review

Instructions

Starting Data