Several UIAlertViews for a delegate

问题:

Currently I've got a class popping up UIAlertViews here and there. Currently, the same class is the delegate for these (it's very logical that it would be). Unfortunately, these UIAlertViews will call the same delegate methods of the class. Now, the question is - how do you know from which alert view a delegate method is invoked? I was thinking of just checking the title of the alert view, but that isn't so elegant. What's the most elegant way to handle several UIAlertViews?

回答1:

Tag the UIAlertViews like this:

#define kAlertViewOne 1
#define kAlertViewTwo 2

UIAlertView *alertView1 = [[UIAlertView alloc] init...
alertView1.tag = kAlertViewOne;

UIAlertView *alertView2 = [[UIAlertView alloc] init...
alertView2.tag = kAlertViewTwo;

and then differentiate between them in the delegate methods using these tags:

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex {
    if(alertView.tag == kAlertViewOne) {
        // ...
    } else if(alertView.tag == kAlertViewTwo) {
        // ...
    }
}

回答2:

FYI, if you want to target just iOS 4 users (which is reasonable now that ~98.5% of clients have at least iOS 4 installed), you should be able to use Blocks to do really nice inline handling of UIAlertViews.

Here's a Stackoverflow question explaining it:
Block for UIAlertViewDelegate

I tried using Zachary Waldowski's BlocksKit framework for this. His UIAlertView(BlocksKit) API reference looked really good. However, I tried to follow his instructions to import the BlocksKit framework into my project, but unfortunately I couldn't get it to work.

So, as Can Berk Güder suggests, I've used UIAlertView tags for now. But at some point in future I'm going to try to move to using Blocks (preferably one which supports ARC out of the box)!

回答3:

easier & newer

UIAlertView *alert = [[UIAlertView alloc] init...
alert.tag = 1;

UIAlertView *alert = [[UIAlertView alloc] init...
alert.tag = 2;



- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex {
    if(alertView.tag == 1) {
        // first alert...
    } else  {
        // sec alert...
    }
}

all done!

回答4:

You can overcome this whole ordeal and prevent yourself from using tags by enhancing UIAlertView to use block callbacks. Check out this blog post I wrote on the subject.

回答5:

I've always thought using tags is a bit of a hack. If you do use them, at least set some defined constants for the tag numbers.

Instead, I use properties like this:

In the interface section:

@property (nonatomic, weak) UIAlertView *overDueAlertView;
@property (nonatomic, weak) UIAlertView *retryPromptAlertView;

Creating the alert view:

UIAlertView *alert = [[UIAlertView alloc] init...
self.overDueAlertView = alert;
[alert show];

Delegate method:

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex {
  if (alertView == self.overDueAlertView) {
    // Overdue alert
  } else if (alertView == self.retryPromptAlertView) {
    // Retry alert
  }