Tweets
Tengo al vaquero del BNR acojonado :-) Cada semana visita la web de @invasivecode mirando que pasa en CA.1 day ago from Twitter for iPad
Product roadmap for the next generation payment system... this is running smoothly... wonderful4 days ago from Tweetie for Mac
First meeting of the day, done... fantastic result... now product roadmap @invasivecode guys, we have more work to do... ;-)4 days ago from Tweetie for Mac
iPhone User Alerts
In Cocoa, you can send alert to the user sending NSAlert class. In Cocoa Touch, you can achieve the same result using the UIAlertView and UIActionSheet classes.
UIAlertView
UIAlertView allows you to send messages to the user. To use an alert in your class, it should be conform to the UIAlertViewDelegate protocol. In this way, when one of the alert buttons is pressed, the following method can be called:
1 | - (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex; |
To launch an alert is very simple. In your delegate class, you call the following method:
1 2 3 4 5 | - (id)initWithTitle:(NSString *)title message:(NSString *)message delegate:(id)delegate cancelButtonTitle:(NSString *)cancelButtonTitle otherButtonTitles:(NSString *)otherButtonTitles,... |
As an example, you can call in your class the following lines of code:
1 2 3 4 5 6 7 8 | UIAlertView *alert; alert = [[UIAlertView alloc] initWithTitle:@”Alert” message:@”This is an alert” delegate:self cancelButtonTitle:@”Cancel” otherButtonTitles:nil]; [alert show]; [alert release]; |
Once the user has pressed the Cancel button, the previous delegate method -alertView:clickedButtonAtIndex is called and the user answer can be processed. The button index depends on the button position and the index starts with 0.
UIActionSheet
UIActionSheet works in the same way. In this case, the action sheet is needed to ask the user to take a decision. The action sheet can be visualized in a view, from a tab bar or from a navigation bar.
If your class uses an action sheet, it must be conform to the UIActionSheetDelegate protocol. In this way, it will be able to call
1 | -(void) actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex; |
and process the user action.
To launch an action is very simple too. In your delegate class, call the following method:
1 2 3 4 5 | -(id)initWithTitle:(NSString *)title delegate:(<UIActionSheetDelegate>)delegate cancelButtonTitle:(NSString *)cancelButtonTitle destructiveButtonTitle:(NSString *)destructiveButtonTitle otherButtonTitles:(NSString *)otherButtonTitles, ... |
For example, you can do the following:
1 2 3 4 5 6 7 8 | UIActionSheet *action; action = [[UIActionSheet alloc] initWithTitle:@"Action" delegate:self cancelButtonTitle:@"Cancel" destructiveButtonTitle:@"OK" otherButtonTitles:nil]; [action showInView:self]; [action release]; |
Example
Let’s make a small iPhone application using an alert view.
Open Xcode and create a Window-based application. Call it SimpleAlert. Open the SimpleAlertAppDelegate.h file and change it as it follows:
1 2 3 4 5 6 | #import @interface SimpleAlertAppDelegate : NSObject { UIWindow *window; } @property (nonatomic, retain) IBOutlet UIWindow *window; @end |
Notice the UIAlertViewDelegate protocol.
Now, change the SimpleAlertAppDelegate.m file. In the -applicationFinishLaunching method add the following:
1 2 3 4 5 6 7 8 | UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Alert" message:@"This is an alert" delegate:self cancelButtonTitle:nil otherButtonTitles:@"one",@"two",@"three",nil]; [alert show]; [alert release]; [window makeKeyAndVisible]; |
Then, implement the following method:
1 2 3 | - (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex { NSLog(@"You pressed button %d",buttonIndex+1); } |
Build and Run. The following alert will appear on your iPhone.

When you press one of the button a message should appear in the console.
Have a nice coding.
++Geppy
