/locationTrivia-objects-ios-0616

Primary LanguageObjective-COtherNOASSERTION

Location Trivia Objects

Objectives

  1. Create custom class files.
  2. Create, access, and set properties.
  3. Compose initializers.
  4. Write methods that interact with data stored in the instances of a custom class.

Instructions

In the last Location Trivia lab you dealt with a representation of locations using NSDictionary. Now, increase the power of your programming by storing this information in custom classes instead!

  • Open the locationTrivia-objects.xcworkspace file.

I. Create the Custom Classes

Create the class files for FISLocation that inherits from NSObject. This class should have four properties:

  • an NSString called name,
  • a CGFloat called latitude,
  • a CGFloat called longitude, and
  • an NSMutableArray called trivia.

Create the class files for FISTrivium that inherits from NSObject. This class should have two properties:

  • an NSString called content, and
  • an NSUInteger called likes.

On the FISAppDelegate class add a public property:

  • an NSMutableArray called locations.

II. Declare Methods and Define Initial Implementations

On the FISAppDelegate class, declare three methods:

  • allLocationNames that takes no arguments and returns an NSArray,
  • locationNamed: that takes one NSString argument called name and returns a FISLocation object, and
  • locationsNearLatitude:longitude:margin: that takes three CGFloat arguments called latitude, longitude, and margin, and returns an NSArray.

Define these methods to return nil.

On the FISLocation class, declare five methods:

  • init — the default initializer that will be overridden,
  • initWithName:latitude:longitude: — a designated initializer,
  • stringByTruncatingNameToLength: which takes one NSUInteger argument called length and returns an NSString,
  • hasValidData which takes no arguments and returns a BOOL, and
  • triviumWithMostLikes which takes no arguments and returns a FISTrivium object.

Define the initializers to assign to self a call of [super init] and return self.

Define the other three methods to return nil.

On the FISTrivium class, declare two initializers:

  • init — the default initializer that will be overridden, and
  • initWithContent:likes: — a designated initializer.

Define the initializers to assign to self a call of [super init] and return self.

Run the tests with ⌘ U to see that they fail.

III. Build the FISTrivium Class

  1. Define FISTrivium's designated initializer.

  2. Override FISTrivium's default initializer to call the designated initializer. Default instances of FISTrivium should have an empty string for their content and no likes.

Run the test in FISTriviumSpec.m to check the FISTrivium class.

IV. Build the FISLocation Class

Write the Initializers

  1. Define FISLocation's designated initializer.
    Hint: Don't forget to set the trivia property to the initialization of an empty mutable array.

  2. Override FISLocation's default initializer to call the designated initializer. Default instances of FISLocation should have an empty string for their name property Have it pass in an empty string for name, and coordinates pointing to the intersection of the equator and the prime meridian (i.e. Latitude 0º, Longitude 0º).

Write the Method Implementations

  1. Define the stringByTruncatingNameToLength: method to return a substring of the location's name shortened to the number of characters defined by the length argument. This method should handle a length argument integer that exceeds the length of the location's name string; in such a case, it should just return the location's whole name.
    Hint: NSString has a handy method called substringToIndex.

  2. Define the hasValidData method to:

  • return NO if the name property is an empty string or nil,
  • return NO if the latitude property is beyond -90.0 and 90.0,
  • return NO if the longitude property is beyond -180.0 and 180.0 or if it is equal to -180.0 (since this longitude conceptually matches the 180º meridian), and
  • otherwise return YES.
  1. Define the triviumWithMostLikes method to:
  • return nil if the trivia array is empty, otherwise
  • return the FISTrivium object in the trivia array that has the highest value for the likes property.
    Hint: You can accomplish this with either a for in loop & an if statement, or by using NSSortDescriptor.

V. Write the FISAppDelegate Method Implementations

  1. Define the allLocationNames method to return an array of all of the name string properties of the FISLocation objects held in the locations array property.

  2. Define the locationNamed: method to return a FISLocation object whose name string property matches the string submitted to the name argument. If there isn't a match, this method should return nil.
    Hint: You can accomplish with either a for in loop & if statement, or by using NSPredicate.

  3. Define the locationsNearLatitude:longitude:margin: method to return an array of all the locations whose coordinates are within ±margin degrees from the given location.
    Note: This is intended to be a simple implementation of local cartography. The test data only contains locations on Manhattan. You do NOT need to spend time programming for edge cases of detecting locations across the poles or across the 180º meridian. For actual mapping implementations, the Apple framework MapKit would be used.

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