Friday, 8 May 2015

Quick Guide to Writing a Chrome Extension

manifest.json

The manifest file is where your extension and its details are defined. There are many different things you can add to it, but here are a few of the basic things:

  {
    "manifest_version": 2,

    "name": "My Chrome Extension",
    "description": "This extension allows you to do... Anthing!",
    "version": "1.1",

    "browser_action": {
      "default_icon": "icon.png",
      "default_popup": "popup.html"
    },

    "content_scripts": [
      {
        "matches": ["https://www.mysite.com/*"],
        "js": ["jquery.js", "SetupDefaults.js", "ChangeTemplate.js"]
      }
    ],

    "permissions": [
      "storage"
    ],

    "icons": { 
      "128": "icon.png" 
    }

  }


Here's a breakdown on the key things in this file:
  • The browser_action allows you to define an image and HTML file that will be used in a popup window when your extension is clicked on in the Chrome toolbar.
  • The content_scripts allows you to specify that when the URL matches https://www.mysite.com/* the scripts jquery.js, SetupDefaults.js and ChangeTemplate.js will be run.
  • The permissions allows you to specify any permissions you need, for example if you were using chrome.storage then you would need the "storage" permission.

It is important to note that the default_popup HTML file cannot have inline JavaScript in it, and this will need to be specified in the head of the HTML as so:

  <html>
    <head>
      <script src="popup.js"></script>
    </head>
    <body>
    </body>
  </html>


Installing Extension Locally

To install your extension locally you will need to go to Extensions (shown below):



Then make sure Developer Mode is checked, and then click Load Unpacked Directory and select the relevant directory.

Submitting your extension

If you would like to submit your Extension you will need to get a Chrome Web Store developer account. This costs approximate $5 (USD) and is a one-off fee. You can find out more about it on this web store getting started guide.

Core Data for Swift

Having core data enabled for an xCode project allows you to persist data between user sessions. There is an option you should tick when creating the project, and that is to use core data. However, if you have already created your project and made significant process without turning on this option, you can just create a new project and copy across the relevant code from AppDelegate.swift!

Defining Entities

xCode makes it excessively easy to define entities. First, you will need to open the .xcdatamodeld file and click "Add Entity", your new entity will appear under the list of entities and you can double click on it to rename it. Adding attributes can be done by pressing the "+" in the attributes section. Attributes need to start with a lowercase name, and some names are reserved such as "isDeleted". You can then select what data type that attribute will be stored as. Your finished entity should look something like this:



There is also a view which allows you to edit entities and add relationships in a UML style format. If you would prefer that change the "Editor Style" which is located in the bottom right.

Defining Relationships

You are also able to define relationships between entities. Once a relationship is created, you can view its details and set properties such as how deletes are handled. For example, when a scenario is deleted I want all stones linked to it to also be deleted, so I set the "Delete Rule" to cascade. Once you have finished defining your relationships you should should have something that looks like this:



The above diagram shows that a Stone entity has one Scenario entity, and a Scenario entity has many Stone entities.

Creating Entities


  func createScenario() {
    let appDelegate = UIApplication.sharedApplication().delegate 
         as! AppDelegate
    let context = appDelegate.managedObjectContext!
        
    //Getting entity description for entity named "Scenario"
    //and creating object to save from it     
    let scenarioEntityDescription =  NSEntityDescription
         .entityForName("Scenario", inManagedObjectContext: context)!
    var scenario =  NSManagedObject
                     (entity: scenarioEntityDescription,
                      insertIntoManagedObjectContext: context)
        
    //Setting entity's attributes.  
    scenario.setValue(nameTextField.text, forKey: "name")
    scenario.setValue(descriptionTextField.text, forKey: "scenario")
    scenario.setValue(tagTextField.text, forKey: "tag")

    //Adding stone for stones relationship.
    //Excluded setting of the "Stone" entity's attributes 
    //for brevity.
    //First step is to get a set for the "stones" 
    //relationship from the scenario.
    var stonesSet = scenario.mutableSetValueForKey("stones")
    let stoneEntityDescription = NSEntityDescription
         .entityForName("Stone", inManagedObjectContext: context)!
    var stoneEntity = NSManagedObject
                       (entity: stoneEntityDescription,
                        insertIntoManagedObjectContext: context)
    stonesSet.addObject(stoneEntity)

    //Setting the stones relationship for the scenario.
    //Saving, please note error handling was excluded.
    scenario.setValue(stonesSet, forKey: "stones")
    context.save(nil)
  }


Fetching Entities


  //Returns an NSArray of all "Scenario" entities.
  //If you want to modify this array (add/remove) then you will need
  //a NSMutableArray using scenarios.mutableCopy() as! NSMutableArray.
  func fetchScenarios() -> NSArray {
    let appDelegate = UIApplication.sharedApplication().delegate 
         as! AppDelegate
    let context = appDelegate.managedObjectContext!
        
    //Setting up request for entity named "Scenario"
    //You can also specify search constraints.     
    var request = NSFetchRequest(entityName: "Scenario")
    request.returnsObjectsAsFaults = false
        
    //Fetching all "Scenario" entities.
    //It will also load all "Stone" entities linked
    //with a "Scenario" entity by "stones" relationship.
    return context.executeFetchRequest(request, error: nil)!
  }


Updating Entities


  //Update the "tag" attribute of a given "Scenario" entity.
  func changeScenarioTag(scenario: NSManagedObject, newTag: String) {
    let appDelegate = UIApplication.sharedApplication().delegate 
         as! AppDelegate
    let context = appDelegate.managedObjectContext!
    
    //Making change to the "Scenario" entity's "tag" attribute.
    //Committing the change.
    scenario.setValue(newTag, forKey: "tag")
    context.save(nil)
  }


Deleting Entities


  func deleteScenario(scenario: NSManagedObject) {
    let appDelegate = UIApplication.sharedApplication().delegate 
         as! AppDelegate
    let context = appDelegate.managedObjectContext!
    
    //Telling context we want to delete the scenario object.
    //As we specified a cascade delete in our relationship "stones"
    //the "Stone" entities linked with the "Scenario will be deleted also.
    context.deleteObject(scenario)

    //Commiting delete.
    context.save(nil)
  }


Tuesday, 5 May 2015

Swift Constructors

If you are interested in creating your own subclass of one of Swift's built in objects, you may often want to pass in additional arguments to the constructor. However, it isn't immediately obvious how to do this. The following code shows you how:

    override init(frame: CGRect) {
        super.init(frame: frame)
    }

    convenience init(color: UIColor, bounds: CGRect) {
        self.init(frame: bounds)
        self.color = color
    }


    // will give you an error if you try to compile without this
    // after adding the above constructors
    required init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }



To explain this a bit further, when you implement a custom constructor you will get an error if you don't implement the required constructor. The constructor you define must be prefixed with convenience and should make a call to the parent class constructor. However, you cannot make the call to the parent class constructor directly from your convenience constructor. The first constructor overrides and then calls the parent constructor so that you can make a call to it.

Friday, 1 May 2015

Preventing Backwards Navigation from a Bar Button Item in Swift

Hello there, sometimes you wish to return to the root view controller when you click on a bar button item in the navigation bar of an app with a navigation controller. For example, you may save something that you don't want the user to be able to go back to. Fortunately, there is away to do this and it is by using a segue with an identifier.
  1. Create a segue from your Bar Button Item
  2. Click on your segue and give it an identifier
  3. Implement the following function in the view controller which has the bar button you added a segue for:

    override func shouldPerformSegueWithIdentifier(identifier: 
        String?, sender: AnyObject?) -> Bool {
        
        if (identifier == "save") {
            saveBoard()
        }
        
        self.navigationController?
            .popToRootViewControllerAnimated(true)
        
        return false
    }


The above handles 2 different segues in my project, one is cancel in which case I want to return to the root view controller without having the ability to go back to my board that I decided I no longer wanted to save. The other is save, when my saving segue is called I want to call my function which saves the board and then goes back to the root view controller. The boolean returned by the function specifies whether the segue was cancelled or not... I returned false as I wanted to handle the navigation back to the root view controller by myself in all cases. The function shouldPerformSegueWithIdentifier could also be useful to implement if you wanted to validate the data a user entered before navigation.

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