How to elegantly transition images in slide show? - objective-c

Question

After some research on here I found a solution to creating a slide show of images in an iphone app. All working fine, currently the images show one after another.
My question is, can I make the images cross dissolve/fade rather than just appearing, and if so could I get some advice on that.
My Code
.m
}
int topIndex = 0, prevTopIndex = 1;
- (void)viewDidLoad
{
imagebottom = [[UIImageView alloc] initWithFrame:CGRectMake(0,0,160,240)];
[self.view addSubview:imagebottom];
imagetop = [[UIImageView alloc] initWithFrame:CGRectMake(0,0,160,240)];
[self.view addSubview:imagetop];
imageArray = [NSArray arrayWithObjects:
[UIImage imageNamed:#"image1.png"],
[UIImage imageNamed:#"image2.png"],
[UIImage imageNamed:#"image3.png"],
[UIImage imageNamed:#"ip2.png"],
nil];
NSTimer *timer = [NSTimer timerWithTimeInterval:5.0
target:self
selector:#selector(onTimer)
userInfo:nil
repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:timer forMode:NSDefaultRunLoopMode];
[timer fire];
[super viewDidLoad];
}
-(void)onTimer{
if(topIndex %2 == 0){
[UIView animateWithDuration:5.0 animations:^
{
imagebottom.alpha = 0.0;
}];
imagetop.image = [imageArray objectAtIndex:prevTopIndex];
imagetop.image = [imageArray objectAtIndex:topIndex];
}else{
[UIView animateWithDuration:5.0 animations:^
{
imagetop.alpha = 1.0;
}];
imagetop.image = [imageArray objectAtIndex:topIndex];
imagebottom.image = [imageArray objectAtIndex:prevTopIndex];
}
prevTopIndex = topIndex;
if(topIndex == [imageArray count]-1){
topIndex = 0;
}else{
topIndex++;
}

Answer 1

You have a bunch of options. If you have a "container" view, you can make a new UIImageView transparent (alpha = 0), then use a UIView animation block to fade one image in and the other out (or leave alpha = 1 on both and slide one in from any side you want.
For instance, you have your main view, self.view. You have one UIImageView *oldView, that is now at rect (0,0,320,100) and you want to slide it to the right as you slide a newView imageView in. First you set the newView frame to (-320,0,320,100) then [self.view addSubview newView]. To animate the change:
[UIView animateWithDuration:2 animations:^
{
oldView.frame = CGRectMake(320, 0, 320, 100);
newView.frame = CGRectMake(0,0,320, 100);
}
completion:^(BOOL finished)
{
[oldView removeFromSuperView];
} ];
You also have the option of using UiView's
+ (void)transitionFromView:(UIView *)fromView toView:(UIView *)toView duration:(NSTimeInterval)duration options:(UIViewAnimationOptions)options completion:(void (^)(BOOL finished))completion
which gives you more/different options (and its less work too!). For instance, using the same basic objects in the first example, but the newView having the same frame as the oldView:
transitionFromView:oldView toView:newView duration:2 options: UIViewAnimationOptionTransitionCrossDissolve completion:^(BOOL finished)) { /*whatever*/}];