iphone - Getting text from UIAlertView

Question

I'm trying to get text from an alert view and add it to my mutable array to list in a table view. I realize there is a similar question that was posted a few months ago, but I dont understand how to utilize the given answer.

-(IBAction)insert {
    UIAlertView* dialog = [[UIAlertView alloc] init];
    [dialog setDelegate:self];
    [dialog setTitle:@"Enter Name"];
    [dialog setMessage:@" "];
    [dialog addButtonWithTitle:@"Cancel"];
    [dialog addButtonWithTitle:@"OK"];

    UITextField *nameField = [[UITextField alloc] initWithFrame:CGRectMake(20.0, 45.0, 245.0, 25.0)];
    [nameField setBackgroundColor:[UIColor whiteColor]];
    [dialog addSubview:nameField];
    [dialog show];

    [data addObject:[nameField text]];
    [mainTableView reloadData];

However my app crashes because it says I'm attempting to insert a nil object at index 0. What am I doing wrong?

EDIT: Ok I think I'm missing a method to handle the alertview. So I found this:

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex {
    NSString *buttonTitle=[alertView buttonTitleAtIndex:buttonIndex];
    if([buttonTitle isEqualToString:@"Cancel"]) {
        return;
    }
    else if([buttonTitle isEqualToString:@"Ok"]) {
        [data addObject:nameField.text];

    }

Now I just need to connect the pieces, but not sure how.

Answer 1

A common mistake that people make when using a UIAlertView is that they think that sending it a show message will block the main thread. It does not. Your code continues to execute, even though there is an alert on the screen. Thus, no value exists for the UITextField that you have passed in.

What you need to do is implement the UIAlertViewDelegate in your UIViewController to grab whatever a user has entered into the text field. That said, you still have to check for a nil value, because if you don't type anything in, the text value will be nil.

UPDATE: This answer was posted before Apple created an API for adding a UITextField to an alert through the UIAlertViewStyle. Here is the updated code, borrowed from @matt

UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Enter Name"
                                                message:@"  "   
                                               delegate:self 
                                      cancelButtonTitle:@"Cancel"
                                      otherButtonTitles:@"OK", nil];
alert.alertViewStyle = UIAlertViewStylePlainTextInput;
[alert show];

Then, in the UIAlertViewDelegate call back:

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex {
    if (buttonIndex == 1) {
        NSString *name = [alertView textFieldAtIndex:0].text;
        // Insert whatever needs to be done with "name"
    }
}