Creating a Custom Tab Bar - sammanthp007/Linux-Kernel-Development GitHub Wiki

Sometimes the standard iOS tab bar just doesn't have the look or functionality you need for your app. In this case, you need to create a custom tab bar from scratch.

Step 1: Setup your Storyboard

• Add a UIViewController to storyboard to function as your main tab bar ViewController.
• Add UIView to serve as the bar part of the Tab Bar.
• Add UIButtons for each tab.
  • Configure their default and selected images.
  • Set the tag value of each button starting with 0 for the first button, 1 for the second and so on.

• Add a UIView that fills the screen above the tabBar. This will serve as our content view.
• Add UIViewControllers that correspond to each tab. (5 tabs = 5 ViewControllers)
• Give each UIViewController a unique Storyboard ID.
• Add what ever content you want in each ViewController. (We will be pulling in the content from a particular ViewController when it's respective tab is tapped.)

Step 2: Hook up IBOutlets

• Create an outlet for the contentView by ctrl + drag

Creating an array of buttons will help us easily keep track of what button is getting pushed based on the tag or index of the button.

• Create an IBOutlet array named, buttons to hold your tab bar buttons.
  • @IBOutlet var buttons: [UIButton]!
  • ctrl + drag outlets from all your buttons to the array.

Step 3: Create Your Instance Variables (global variables)

• Define variables to hold each ViewController associated with a tab.

var homeViewController: UIViewController!
var searchViewController: UIViewController!
var accountViewController: UIViewController!
var trendingViewController: UIViewController!

We will use an array to hold all our ViewControllers. That way, we can simply pluck out any particular ViewController we want based on the button that was pushed.

• Define a variable for an array to hold the ViewControllers named, viewControllers.

var viewControllers: [UIViewController]!

• Define a variable to keep track of the tab button that is selected. Set it to an initial value of 0. We will link the button's tag value to this variable. So an initial value of 0 will reference our first button.

var selectedIndex: Int = 0

Step 4: Link your ViewController Variables to the ViewControllers in the Storyboard.

Remember, all the ViewControllers we create in the Storyboard don't actually exist, until we set up a link to them somehow, like a segue. For our custom tab bar, we won't be using segues, so we will have to instantiate them when our main tab bar ViewController first loads.

• Within the ViewDidLoad() method, access the main Storyboard through code.

let storyboard = UIStoryboard(name: "Main", bundle: nil)

• Next, instantiate each ViewController by referencing storyboard and the particular ViewController's Storyboard ID

homeViewController = storyboard.instantiateViewControllerWithIdentifier("HomeViewController")

Step 5: Add each ViewController to your viewControllers array

viewControllers = [homeViewController, searchViewController, accountViewController, trendingViewController]

Step 6: Create a Shared Action for the Buttons.

Since we will be keeping track of which button was tapped, all the buttons can share the same action method.

• ctrl + drag from your first button to the TabBarViewController to create an action.
  • Name it something like didPressTab.
  • Change the Type from AnyObject to UIButton (that way we can access special properties only buttons have)
  • ctrl + drag from every other button to the same didPressTab so they are all sharing.

Step 7: Get Access to the Previous and Current Tab Button.

When a new tab button is tapped, the goal of this method is to get rid of the ViewController contents that was previously being displayed in the tabBarViewController, and replace it with the new ViewController content that corresponds to the new tab button that was pushed. In order to do this, we need to know two things: the previous Button and ViewController that were selected and the current Button and ViewController that are now selected.

The selectedIndex will store the tag value of whatever button is selected. We set the initial value of selectedIndex to 0, or button 1. When we tap a different button, until we assign selectedIndex the tag value of the new button that was pushed, it actually represents the tag value of the previous button.

• So, within the didPressTab method, we can keep track of the previous button like this...

let previousIndex = selectedIndex

Remember when we changed AnyObject to UIButton when we hooked up our action? That is so we can access special properties of buttons, like accessing their tag value.

• Set the selectedIndex to the tag value of which ever button was tapped.

selectedIndex = sender.tag

You might be wondering why we don't just call selectedIndex, selectedTag instead. The reason is because we are going to plug that number into our buttons and ViewControllers arrays in order to pluck out the correct item. When you access an item from an array at a certain point, buttons[0] or viewControllers[3], that point is called the index. The items in an array start at index 0 and go up by a value of 1 each item so that the 2nd item is at index 1, the 3rd is index 2 and so on.

So as you can see, it is no coincidence that we set our first button tag value to be 0, and then stored it at index 0 in our buttons array; just as we did for the corresponding index locations of the ViewControllers stored in our viewControllers array.

Step 8: Remove the Previous ViewController and Set Button State.

• Within your didPressTab method, use your previousIndex value to access your previous button and set it to the non-selected state.

buttons[previousIndex].isSelected = false

• Use the previousIndex to access the previous ViewController from the viewControllers array.

let previousVC = viewControllers[previousIndex]

• Remove the previous ViewController

previousVC.willMove(toParentViewController: nil)
previousVC.view.removeFromSuperview()
previousVC.removeFromParentViewController()

Step 9: Add the New ViewController and Set Button State.

• Within your didPressTab method, access your current selected button and set it to the selected state.

sender.isSelected = true

• Use the selectedIndex to access the current ViewController from the viewControllers array.

let vc = viewControllers[selectedIndex]

• Add the new ViewController. (Calls the viewWillAppear method of the ViewController you are adding)

addChildViewController(vc)

• Adjust the size of the ViewController view you are adding to match the contentView of your tabBarViewController and add it as a subView of the contentView.

vc.view.frame = contentView.bounds
contentView.addSubview(vc.view)

• Call the viewDidAppear method of the ViewController you are adding using didMove(toParentViewController: self).

vc.didMove(toParentViewController: self)

Step 10: Set the Initial Tab when the App Starts.

We will probably want to set a default tab to be initiated when we start our app for the first time. You can specify what tab you want to start with by setting the initial value of, selectedIndex. Since we set the initial value of selectedIndex to 0, our app will load with the 1st tab initiated.

• Within the viewDidLoad method, near the bottom, set the button state and call the didPressTab method. We will plug in buttons[selectedIndex] as arguments in the didPressTab method to specify the initial button, since we haven't actually "tapped" a button yet and there is no sender to access.

buttons[selectedIndex].isSelected = true
didPressTab(buttons[selectedIndex])

Step 11: Run Your App!!!