3 things every programmer should know

Many students obtain their degree and they don't know about the practice of programming. I consider three skills essential and unfortunately they are not always taught.

Step by step

When writing any piece of code, don't write everything and then start testing. You are heading for a long debugging session. Instead, you should write the smallest piece of code that improves the behavior and test that it did not break anything. Ideally you should run a full regression suite, but most people won't have this. At least you should run the code once.

Version control and diff tools

This step by step approach brings me to the next thing. Use version control! Version control allows you to document these incremental steps you made. And what is even better, it allows you to easily see what changes were made (use the diff tool) and where the bug might be.

Debugger

Finally, many starting developers do not know of debuggers. These are wonderful tools that can help you pinpoint the precise point a problem appears.

Summary

So, make sure that, by the time you start programming for a living, you work step by step, use version control and use the debugger.

Segues in iOS

One of the most used patterns in iOS programming are passing data from an initial view controller to a target view controller and the inverse pattern. Hence this post.

Forward segues

In the initial controller, you need to define the action before the segue is taken:

brush: swift
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "NameOfSegue" {
        if let destinationViewController = segue.destinationViewController as? DestinationViewController {
            destinationViewController.parameter = whatever
        }
    }
}

The segue indentifier is defined in Interface Builder. The code above passes whatever argument to the destinationViewController. The destination gets all the data already initialized before the viewDidLoad function.

You never call prepareForSegue directly. It’s a message from UIKit to let you know that a segue has just been triggered.

We can define what is passed as the sender when we perform the segue programatically:

brush: swift
@IBAction func tappedButton(sender: AnyObject) {
    performSegueWithIdentifier("NameOfSegue", sender: UIColor.blueColor())
}

Unwind segues

Unwind segues are used to pop view controllers from the stack. a function must be defined in the destination controller and marked as an IBAction.

brush: swift
@IBAction func detailViewClosed(segue:UIStoryboardSegue) {
  if let detailsViewController = segue.sourceViewController as? DetailViewController {
    self.name = detailsViewController.name
  }
}

Information can be prepared in the source controller with the prepareForSegue function, as in the forward segue case.

UIKit uses the function canPerformUnwindSegueAction to determine how low in the view stack it has to go:

brush: swift
override func canPerformUnwindSegueAction(action: Selector, fromViewController: UIViewController, withSender sender: AnyObject) -> Bool {
  if (self.respondsToSelector(action)) {
    return self.unwindHere;
  }
  return false;
}

C designated initializers

Assigning values to a structure at declaration time was confusing because it was not clear what field from the structure was being initialized. Also, adding a new field to the structure could break existing code.

C99 fixed this with designated initializers:

brush: c
struct my_struct { int field1; int field2; };
struct my_struct s = { .field1 = 2, .field2 = 4 };

Fields can be given in any order and can be omitted as needed.

Arrays can also benefit from this to create clearer code:

brush: c
int unit_array[3][3] = {
  [0][0] = 1,
  [1][1] = 1,
  [2][2] = 1
};