Displaying images in sequence with a loop

问题:

I got an NSArray with 5 pictures. I want to display them one after the other in a loop. My code :

 NSArray *tabImage = [[NSArray alloc] init];

tabImage = [[NSArray arrayWithObjects:  
               [UIImage imageNamed:@"picto_1.png"],
               [UIImage imageNamed:@"picto_2.png"],
               [UIImage imageNamed:@"picto_3.png"],
               [UIImage imageNamed:@"picto_4.png"],
               [UIImage imageNamed:@"picto_5.png"],
               nil] retain];

int var = 0;
var = indexPath.row;

for (int var = 0; var < 20; var++) {
    pictoImage.image = [tabImage objectAtIndex:(var % 5)];
}

I got the same picture all the time.

Thanks for help.

回答1:

I’m guessing pictoImage is an UIImageView. In that case look at the class reference, specifically the animationImages properties.

 pictoImage.animationImages = [NSArray arrayWithObjects:  
                                   [UIImage imageNamed:@"picto_1.png"],
                                   [UIImage imageNamed:@"picto_2.png"],
                                   [UIImage imageNamed:@"picto_3.png"],
                                   [UIImage imageNamed:@"picto_4.png"],
                                   [UIImage imageNamed:@"picto_5.png"],
                                   nil];

 // How many seconds it should take to go through all images one time.
 pictoImage.animationDuration = 5.0;

 // How many times to repeat the animation (0 for indefinitely).
 pictoImage.animationRepeatCount = 4;

 [pictoImage startAnimating];

回答2:

You are not giving the framework time to actually render the images to the window.

All your updates are being coalesced into one "setNeedsDisplay" call. On the next iteration of the run loop, the image view will be rendered using the last image that you set in the loop.

回答3:

If pictoImage is an UIImageView, @Hagelin's answer is the best way to go. Now, if pictoImage is not an UIImageView object then you will have to take a different approach and that definitely is not a loop.

Set an NSTimer with a desired time interval and invoke a method that updates pictoImage iterating over the tabImages. It should be something like this :-

- (void)setup {
    ...

    [NSTimer scheduledTimerWithTimeInterval:2.0
                                     target:self
                                   selector:@selector(updatePictoImage:)
                                   userInfo:nil
                                    repeats:YES];

    ...
}

- (void)updatePictoImage:(NSTimer*)theTimer {
    static int i = 0;
    if ( i > 20 ) {
        pictoImage.image = [tabImages objectAtIndex:(i % 5)];
    } else {
       [theTimer invalidate];
    }
}

This should update the pictoImage every 2 seconds with images in tabImages.

回答4:

You don't print anything.

You are overriding the contents of your pictoImage 20 times in a row, leaving it with the last assignment when var is 19, so it should be picto_4.png.

Also, the whole var declaration doesn't make much sense at all... first you set it to 0, then you set it to indexPath.row, and in the loop it is completely redefined....