Lecture 12

Cay S. Horstmann

Lecture 12 Question 1

Which of these is the correct code to compute the number of seconds since 1970?

1. NSDate now = [NSDate date];
   double seconds = [now timeIntervalSince1970];    

2. NSDate* now = [NSDate date];
   double seconds = [now timeIntervalSince: 1970];

3. NSDate now = new NSDate();
   double seconds = now.timeIntervalSince(1970);

4. double seconds = [[NSDate date] timeIntervalSince1970];

Lecture 12 Question 2

Which of the following code snippets will compile and run without an exception?

1. NSDate* now = [NSDate init];
   double seconds = [now timeIntervalSince1970];

2. NSDate* now = nil;
   double seconds = [now timeIntervalSince1970];

3. NSDate* now = [NSDate new];
   double seconds = [now timeIntervalSince1970];

4. None of the above

Outlets and Actions

• Outlet: A UI control in a xib file with a corresponding property in a controller class to access it
• @property (nonatomic, retain) IBOutlet UIButton *myButton;
• IBOutlet is #defined to the empty string, just a signal to the GUI builder
• Action: Method that can be triggered by a UI control in a xib file
• - (IBAction)doSomething:(id)sender;
• IBAction is #defined to void, another signal to the GUI builder

Protocols

• Like interfaces in Java: methods that a class needs to implement
• Put in angle brackets:

  @interface SJSUAppDelegate : UIResponder <UIApplicationDelegate>

• SJSUAppDelegate.m defines the methods of the UIApplicationDelegate protocol

Action Sheets and Alerts

• Action sheets force the user to make a choice
• Alerts force the user to acknowledge information
• To use an action sheet, view controller must conform to UIActionSheetDelegate protocol

Action Sheets and Alerts

• To show an action sheet:

  UIActionSheet *actionSheet = [[UIActionSheet alloc]
     initWithTitle:@"Are you sure?"
     delegate:self
     cancelButtonTitle:@"No Way!"
     destructiveButtonTitle:@"Yes, I'm Sure!"
     otherButtonTitles:@"Foo", @"Bar", nil];
  [actionSheet showInView:self.view];    
    

Action Sheet Buttons

• Responding component must implement UIActionSheetDelegate protocol
• To react to button, implement actionSheet:didDismissWithButtonIndex in the controller.
• Get button index as parameter:

  - (void)actionSheet:(UIActionSheet *)actionSheet
  didDismissWithButtonIndex:(NSInteger)buttonIndex
  {
     if (buttonIndex != [actionSheet cancelButtonIndex])
     {
        ...      
     }
  }

Alerts

• Show alert:

  NSString *msg = ...;
  UIAlertView *alert = [[UIAlertView alloc]
     initWithTitle:@"Something was done"
     message:msg
     delegate:self
     cancelButtonTitle:@"Phew!"
     otherButtonTitles:nil];
  [alert show];
  

• No button action needed if only one

Reading Before Next Class

• Dr. Pollett recommends the book by Mark, Nutting, and LaMarche for learning iOS programming.
• Safari unfortunately only has the iOS 5 edition, but it is ok for this course
• Read chapter 4

Lab

• Bring your laptop to each class
• Always work with a buddy
• One of you writes code, the other types up answers
• Switch roles each lab (not each day)
• Submit lab work to Piazza

Image and Text

• Make a new project lab12 just like last time
• Look at SJSUAppDelegate.m. Which methods come from the superclass? Which come from the UIApplicationDelegate protocol?
• Add an image of yourself to your Supporting Files folder
• Open the xib file and add an image view. Set the image to the one you just supplied.
• Add two labels Username and PIN and two text fields
• For the text fields, we edit their Placeholder attribute to hint at what the user should be entering in that text field. Use hints like "Your username" and "Your personal ID number"
• Make sure the Clear When Editing check box beneath this attribute is checked so the hint text vanishes when people start typing
• For the second text field, set the keyboard to Number Pad
• Run the app. What happens when you click on the second field?
• How do you make the keyboard go away?

Managing the Keyboard

• Make outlets for the nameField and passwordField. They both have type UITextField
• Make an action

  - (IBAction)textFieldDoneEditing: (id)sender; 

  and attach it to the Did End on Exit event of each text field
• Implement the method as

  [sender resignFirstResponder];

• Run your app. How can you now make the keyboard go away?

Hiding the Keyboard With a Background Tap

• Most iOS apps hide the keyboard when you tap somewhere in the background
• How do we implement that? The textbook says “The answer is probably going to surprise you because of its simplicity”. Well, what surprised me is that an app author has to worry about plumbing like that. Whatever. here goes. First, add another action

  - (IBAction)backgroundTap:(id)sender {
  [self.nameField resignFirstResponder];
  [self.numberField resignFirstResponder];
  }

• Select the xib file again. Make sure your dock is in list mode (click the triangle icon to the bottom right of the dock to switch to list view). Single-click View so it is selected. Do not select one of your view’s subitems. We want the container view itself.
• Bring up the Identity inspector. The Class should be UIView. (If not, did you select the background?) Change that to UIControl.
• Now link the Touch Down event to the backgroundTap action.
• Run the program. Try entering a user name and PIN code. Then touch on the image. What happens? Why?
• Were you surprised by the simplicity?

Action Sheets

• When the user touches the image, pop up an action sheet of your choice. How do you do that?
• Add a handler for the Ok button of the action sheet that pops up an alert that says "Hello, (user name from the text field), you can now relax!". How do you do that?
• You should be able to do these tasks with what you have learned about iOS programming, but if you need more step-by-step detail, read ch. 4 of the text that Dr. Pollett recommends.