1€ Displaying Alerts with UIAlertView

Figure 2-1. An alert view telling the user that she needs an active internet connection



The best way to initialize an alert view is, of course, through using its designated initializer:

UIAlertView *alertView = [[UIAlertView alloc]

initWithTitle:@"Title"

message:@"Message"

delegate:nil

cancelButtonTitle:@"Cancel"

otherButtonTitles:@"Ok", nil];

[alertView show];



2.1 Displaying Alerts with UIAlertView | 111



When this alert view is displayed to the user, she will see something similar to that

shown in Figure 2-2:



Figure 2-2. A simple alert view displayed to the user



In order to display an alert view to the user, we use the alert view's show method. Let's

have a look at the description for each one of the parameters that we passed to the

initializer of the alert view:

title



This is the string that the alert view will display on the top when it is shown to the

user. This string is Title in Figure 2-2.

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message



This is the actual message that gets displayed to the user. In Figure 2-2, this message

is set to Message.

delegate



This is the optional delegate object that we pass to the alert view. This object will

then get notified whenever the alert's state changes, for instance, when the user

taps on a button on the alert view. The object passed to this parameter must conform to the UIAlertViewDelegate protocol.

cancelButtonTitle



This is a string that will get assigned to the cancel button on an alert view. An alert

view that has a cancel button usually asks the user for an action. If the user isn't

comfortable with performing that action, he or she will press the cancel button.

This button's title does not necessarily have to say Cancel. It is up to you to specify

a title for this button. This parameter is optional.

otherButtonTitles



Any other buttons that you want to have apear on the alert view, you pass their

titles here. Separate the titles with a comma and make sure you terminate the list

of titles with a nil or as it's called, a sentinel. This parameter is optional.

It is possible to create an alert view without any buttons. An alert view

without a button cannot be dismissed by the user so you, as the programmer, need to make sure this alert view will get dismissed automatically, for instance, 3 seconds after it is displayed. An alert view without

any buttons that does not dismiss itself automatically gives a really poor

user experience and not only will your app get low ratings on the App

Store for blocking the UI from user-access, chances are that your app

will get rejected by Apple.



Alert views can take various styles. The UIAlertView class has a property called alert

ViewStyle of type UIAlertViewStyle:

typedef enum {

UIAlertViewStyleDefault = 0,

UIAlertViewStyleSecureTextInput,

UIAlertViewStylePlainTextInput,

UIAlertViewStyleLoginAndPasswordInput

} UIAlertViewStyle;



Here is what each of these styles will do:

UIAlertViewStyleDefault



This is the default style of an alert view, as we saw in Figure 2-2.

UIAlertViewStyleSecureTextInput



With this style, the alert view will contain a secure text field for secure text entry.

For instance, if you are asking the user for her online banking credentials, then you

can potentially use this style of alert view.

2.1 Displaying Alerts with UIAlertView | 113



UIAlertViewStylePlainTextInput



Under this style, the alert view will display a non-secure text field to the user. This

style is great if you simply want to ask the user for plain text entry, such as the

user's phone number.

UIAlertViewStyleLoginAndPasswordInput



With this style, the alert view will display two text fields. One non-secure for username and another, a secure text field, for password.

Once you decide that you need to get notified when the user interacts with the alert

view, it is time that you specify a delegate object to your alert view. This delegate must

conform to the UIAlertViewDelegate protocol. The most important method defined in

this protocol is the alertView:clickedButtonAtIndex: method which gets called as soon

as the user taps on one of the buttons in the alert view. The button index is passed to

you through the clickedButtonAtIndex parameter.

Let's, as an example, display an alert view to the user and ask whether she could be

bothered to rate our app in the App Store. We will display two buttons on our alert

view: Yes and No. In our alert view delegate, we will detect which button she tapped

on and will take action accordingly.

Let's first implement two very simple methods that return the title of our two buttons:

- (NSString *) yesButtonTitle{

return @"Yes";

}

- (NSString *) noButtonTitle{

return @"No";

}



Now we need to make sure that we are conforming to the UIAlertViewDelegate protocol

in our view controller:

#import

@interface Displaying_Alerts_with_UIAlertViewViewController

: UIViewController

@end



All good. The next step would be to create and display our alert view to the user:

- (void)viewDidAppear:(BOOL)animated{

[super viewDidAppear:animated];

self.view.backgroundColor = [UIColor whiteColor];

UIAlertView *alertView = [[UIAlertView alloc]

initWithTitle:@"Rating"

message:@"Can you please rate our app?"

delegate:self

cancelButtonTitle:[self noButtonTitle]

otherButtonTitles:[self yesButtonTitle], nil];



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[alertView show];

}



So now, our alert view will look similar to that shown in Figure 2-3:



Figure 2-3. An alert view with Yes and No buttons



Now we need a way to know whether the user selected the Yes or the No option in our

alert view. For this, we will need to implement the alertView:clickedButtonAtIndex:

method of our alert view delegate:

2.1 Displaying Alerts with UIAlertView | 115



- (void)

alertView:(UIAlertView *)alertView

clickedButtonAtIndex:(NSInteger)buttonIndex{

NSString *buttonTitle = [alertView buttonTitleAtIndex:buttonIndex];

if ([buttonTitle isEqualToString:[self yesButtonTitle]]){

NSLog(@"User pressed the Yes button.");

}

else if ([buttonTitle isEqualToString:[self noButtonTitle]]){

NSLog(@"User pressed the No button.");

}

}



As you can see, we are using the buttonTitleAtIndex: method of UIAlertView. We pass

the zero-based index of a button inside that alert view to this method and we will get

the string that represents the title of that button, if any. Using this method, we can

determing which button the user has tapped on. The index of that button will be passed

to us as the buttonIndex parameter of the alertView:clickedButtonAtIndex: method

but if you need the title of that button, you will then need to use the buttonTitleAtIn

dex: method of UIAlertView. That is it; job done!

You can also use an alert view to ask the user for text entry, for instance, if you would

like to ask the user for their credit card number or their address. For this, as mentioned

before, we need to use the UIAlertViewStylePlainTextInput alert view style. Here is an

example:

- (void) viewDidAppear:(BOOL)animated{

[super viewDidAppear:animated];

UIAlertView *alertView = [[UIAlertView alloc]

initWithTitle:@"Credit Card Number"

message:@"Please enter your credit card number:"

delegate:self

cancelButtonTitle:@"Cancel"

otherButtonTitles:@"Ok", nil];

[alertView setAlertViewStyle:UIAlertViewStylePlainTextInput];

/* Display a numerical keypad for this text field */

UITextField *textField = [alertView textFieldAtIndex:0];

textField.keyboardType = UIKeyboardTypeNumberPad;

[alertView show];

}



If we run our app on the simulator now, we will get result similar to that shown here:



116 | Chapter 2: Implementing Controllers and Views



Figure 2-4. An alert view with plain text input



We did change the alert view's style to UIAlertViewStylePlainTextInput in this code

but we did something else as well. We retrieved the reference to the first and the only

text field that we knew we would have on the alert view after changing its style to

UIAlertViewStylePlainTextInput, and we used that text field's reference to change the

keyboard type of the text field. For more information about text fields, please refer to

Recipe 2.14.



2.1 Displaying Alerts with UIAlertView | 117



In addition to a plain text entry, you can ask the user for secure text. You would normally use this if the text that the user is entering needs to be secured. For instance, if

you are asking the user to enter her password. Here is an exmaple:

- (void) viewDidAppear:(BOOL)animated{

[super viewDidAppear:animated];

UIAlertView *alertView = [[UIAlertView alloc]

initWithTitle:@"Password"

message:@"Please enter your password:"

delegate:self

cancelButtonTitle:@"Cancel"

otherButtonTitles:@"Ok", nil];

[alertView setAlertViewStyle:UIAlertViewStyleSecureTextInput];

[alertView show];

}



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Figure 2-5. Secure text entry in an alert view



And as you can see, the style that we've chosen is UIAlertViewStyleSecureTextInput.

This style is very similar to the UIAlertViewStylePlainTextInput style except that the

text field is set to secure the entered text.

The next style which is quite useful displays two text fields. One for username and the

other one for password. So, one plain text entry and the other one secure:

- (void) viewDidAppear:(BOOL)animated{

[super viewDidAppear:animated];

UIAlertView *alertView = [[UIAlertView alloc]



2.1 Displaying Alerts with UIAlertView | 119



initWithTitle:@"Password"

message:@"Please enter your credentials:"

delegate:self

cancelButtonTitle:@"Cancel"

otherButtonTitles:@"Ok", nil];

[alertView setAlertViewStyle:UIAlertViewStyleLoginAndPasswordInput];

[alertView show];

}



And the results will look similar to that shown in Figure 2-6:



Figure 2-6. Login and Password style of alert view



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See Also

XXX



2.2 Creating and Using Switches with UISwitch

Problem

You would like to, through your UI, give your users the ability to turn an option on or

off.



Solution

Use the UISwitch class.



Discussion

The UISwitch class provides an On/Off user control like the ones shown in Figure 2-7 for Auto-Capitalization, Auto-Correction and so on...



2.2 Creating and Using Switches with UISwitch | 121