Creating the Storyboard Example Project

8/11/2019 Creating the Storyboard Example Project

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Creating the Storyboard Example Project

The remainder of this chapter will work through the creation of a simple application using storyboarding to

implementmultiple sceneswith segues defined to allow user navigation.

Begin by launching Xcode and creating a new project using the SingleView Applicationtemplate. On the project

options panel enter storyboardas both the product name and class prefix and make sure that the Use

Storyboardoption is selected before clicking Next. Save the project to a suitable location by clicking on

the Createbutton.

Accessing the Storyboard

Upon creation of the new project, Xcode will have created what appears to be the usual collection of files for a

single view application. Instead of a NIB file for the initial view controller, however, Xcode has created a

storyboard file named MainStoryboard.storyboard. Select this file in theproject navigatorpanel to view the

storyboard canvas as illustrated in Figure 18-1:
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Figure 18-1

The view displayed on the canvas is the view for the storyBoardViewController created for us by Xcode when we

selected the Single View Application template. The arrow pointing inwards to the left side of the view indicates

that this is the initial view and will be the first view displayed when the application launches. Objects may be

added to the view in the usual manner by dragging and dropping items from the Object library (View -> Utilities ->

Show Object Library) onto the view canvas. For the purposes of this example, drag a label and a button onto the

view canvas. Using the properties panel, change the label text to Scene One and the button text to Go to Scene

2:
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Figure 18-2

Adding Scenes to the Storyboard

To add a second scene to the storyboard, simply drag a view controller object from the Object library panel onto

the canvas. Figure 18-3 shows a second scene added to a storyboard:
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Figure 18-3

Drag and drop a label and a button into the second scene and configure the objects so that the view appears as

follows:
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Figure 18-4

As many scenes as necessary may be added to the storyboard, but for the purposes of this exercise will we use

just two scenes. Having implemented the scenes the next step is to configure segues between the scenes.

Configuring Storyboard Segues

As previously discussed, a segue is the transition from one scene to another within a storyboard. Within the

example application, touching the Go to Scene 2 button will segue to scene 2. Conversely, the button on scene 2

is intended to return the user to scene 1. To establish a segue, hold down the Ctrl key on the keyboard, click over

a control (in this case the button on scene 1) and drag the resulting line to the scene 2 view. Upon releasing the

mouse button a menu will appear. Select the Modal menu option to establish the segue. Repeat these steps to

establish a segue between the button on scene 2 and the scene 1 view. As segues are established Interface

Builder displays lines indicating the connections:
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Figure 18-5

As more scenes are added to a storyboard it becomes increasingly difficult to see more than a few scenes at one

time on the canvas. To zoom out simply double click on the canvas. To zoom back in again simply double click

once again on the canvas. Zoom buttons are also provided in the bottom right hand corner of the design canvas.

Configuring Storyboard Transitions

Xcode provides the option to change the visual appearance of the transition that takes place during a segue. By

default a Cover Vertical transition is performed whereby the new scene slides vertically upwards from the bottom

of the view to cover the currently displayed scene. To change the transition, select the corresponding segue line,
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display the attributes inspector (View -> Utilities -> Show Attributes Inspector) and modify the Transition setting.

In Figure 18 6 the transition has been changed to Cross Dissolve:

Figure 18-6

To delete a segue from a storyboard simply select the arrow and press the keyboard delete key.

Associating a View Controller with a Scene

At this point in the example we have two scenes but only one view controller (the one created by Xcode when we

selected Single View Application). Clearly in order to be able to add any functionality behind scene 2 it too will

need a view controller. The first step, therefore, is to add the files for a view controller to the project. Right click

on the storyboard target at the top of the project navigator panel and select New Filefrom the resulting menu.

In the new file panel select UIViewController subclass and click Nextto proceed. On the options screen verify

that the Subclass of menu is set to UIViewController and that the Targeted foriPadand With XIB for user

interfaceoptions are both deselected (since the view already exists in the storyboard there is no need for an NIB

user interface file) and name the class Scene2ViewContoller.

Select the MainStoryboard.storyboardfile in the project navigator panel and select the View Controller button

located in the panel beneath the Scene 2 view as shown in Figure 18-7:
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Figure 18-7

With the view controller for scene 2 selected, display the Identity Inspector (View -> Utilities -> Identity Inspector)

and change the Class from UIViewController to Scene2ViewController:
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Figure 18-8

Scene 2 now has a view controller and corresponding source files where code may be written to implement any

required functionality.

Triggering a Storyboard Segue Programmatically

In addition to wiring up controls in scenes to trigger a segue it is also possible to initiate a preconfigured segue

from within the application code. For the sake of an example, assume that when scene 2 is displayed we want to

segue back to scene 1 if the device is turned upside down. Since there is no way to implement this within the

storyboard canvas in Interface Builder the only option to trigger the segue is from within the code of the

application. Segues are triggered from within code by calling theperformSegueWithIdentifier:method of the

UIViewController class. One of the arguments required by this method is the identifier of the segue to be

performed. By default, segues created in storyboards are not given identifiers. The first step, therefore, is to

assign an identifier to the segue that returns to scene 1 from scene 2. To achieve this, select

the MainStoryboard.storyboardfile in the project navigator and select the segue arrow for the scene 2 to scene 1

segue. Display the Attribute Inspector panel (View -> Utilities -> View Attribute Inspector) and enter the

SegueToScene1 in the Identifier text field.

Next, edit the Scene2ViewController.m file, scroll down to the shouldAutorotateToInterface-Orientation:method

and modify it to trigger the segue when the device detects that it is upside down:

- (BOOL)shouldAutorotateToInterfaceOrientation:

(UIInterfaceOrientation)interfaceOrientation

{

if (interfaceOrientation ==

UIInterfaceOrientationPortraitUpsideDown)

{

[self performSegueWithIdentifier: @"SegueToScene1"

sender: self];

}// Return YES for supported orientations
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return (interfaceOrientation ==

UIInterfaceOrientationPortrait);

}

After making the changes, compile and run the application. Select the button to segue to scene 2 and then rotate

the device so that it is upside down (if using the iOS iPhone Simulator, repeatedly select one of the Hardware ->

Rotatemenu options until the simulator is upside down). This should trigger the segue and cause the transition

back to scene 1.

Performing Tasks before a Segue

Before a segue is performed by the storyboard runtime environment, a call is made to

theprepareForSegue:method of the current view controller. If any tasks need to be performed prior to the segue

taking place simply implement this method in the current view controller and add code to perform any necessary

tasks:

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender

{

NSLog(@"Segue about to be performed");

}

Summary

The new Storyboard feature introduced in Xcode 4.2 allows for the navigational flow between the various views in

an iOS application to be visually constructed without the need to write code. In this chapter we have covered the

basic concepts behind storyboarding and worked through the creation of an exampleiPhone applicationusing

this feature.
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Creating the Storyboard Example Project