When somebody does a wipe gesture to scroll the content from left to right, I would like to have a background image scrolling into the same direction, but at a different speed. Much like what these classic games did do 20 years ago (remember that, anybody????)
I accomplished this by using two UIScrollView instances. The first is where the actual content is displayed, and the second (which is behind the first in z-order) is where I have my slower-moving background. From there the top UIScrollView has a delegate attached to it that gets notified when the contentOffset changes. That delegate, in turn, programatically sets the contentOffset of the background scroller, multiplied against a constant to slow the scroll down relative to the foreground. So, for instance, you might have something like:
// Defined as part of the delegate for the foreground UIScrollView
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
UIScrollView* scroll_view(static_cast<UIScrollView*>(bkg_scroller_m.view));
CGPoint offset(scrollView.contentOffset);
offset.x = offset.x / 3;
offset.y = offset.y / 3;
// Scroll the background scroll view by some smaller offset
scroll_view.contentOffset = offset;
}
You can easily do this by implementing scroll view did scroll with a UIImageView under it...
You'll end up with something like this... with the backgroundImageView being a UIImageView added to the view before the subview... you can layer as much image views as you want without performance issues
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
float factor = scrollView.contentOffset.x / (scrollView.contentSize.width - 320);
if (factor < 0) factor = 0;
if (factor > 1) factor = 1;
CGRect frame = backgroundImageView.frame;
frame.origin.x = factor * (320 - backgroundImageView.frame.size.width);
backgroundImageView.frame = frame;
}
You can do it with CoreAnimation. You'll want to hook into the scrollViewDidEndDragging:willDecelerate: and scrollViewWillBeginDecelerating: UIScrollViewDelegate methods. Then begin an Animation on your image by changing the center position. See this SO article for more on animations.
For example you have multiple scrollviews, want them scroll difference speed. here is the modification code base on Salamatizm answer:
CGSize screenSize = [[UIScreen mainScreen] bounds].size;
float factor = scrollView.contentOffset.x / (scrollView.contentSize.width - screenSize.width);
if (factor < 0) factor = 0;
if (factor > 1) factor = 1;
CGSize parralaxSize = self.parralaxBackgroundView.contentSize;
CGPoint parallaxOffset = CGPointMake(-(factor * (screenSize.width - parralaxSize.width)), 0);
[self.parralaxBackgroundView setContentOffset:parallaxOffset animated:NO];
Related
I Have four pages in single uiscrollView and pageing is enabled. Each page may have different height, I Tried to increase the content size of scrollview in scrollViewDidEndDecelerating delegate but it does't help me.
Can any one suggest how to increment contentsize of scrollview in each page differently?
Thanks in Advance.
That is not possible, the content size is the bounds of the scroll view, it is a rectangle, how could it change for each page? Why not scale the pages so they are the same size and use zooming?
I don't think you can do that natively. What you can try however is to disable paging and do it manually.
There is a useful delegate method for that:
-(void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset;
This let's you set where the scrollView will end its scrolling.
-(void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset{
float offsetY = floorf((*targetContentOffset).y);
float yGoto = 0.0;
// Find out, based on that offsetY in which page you are
// and set yGoto accordingly to the start of that page
// In the following example my pages are 320px each
// I start by only allowing to go 1 page at a time, so I limit
// how far the offsetY can be from the current scrollView offset
if(offsetY > scrollView.contentOffset.y + 160){
// Trying to scroll to more than 1 page after
offsetY = scrollView.contentOffset.y + 160;
}
if(offsetY < scrollView.contentOffset.y - 160){
// Trying to scroll to more than 1 page before
offsetY = scrollView.contentOffset.y - 160;
}
if(offsetY < 0){
// Trying to scroll to less than the first element
// This is related to the elastic effect
offsetY = 0;
}
if(offsetY > scrollView.contentSize.height-320){
// Trying to scroll to more than the last element
// This is related to the elastic effect
offsetY = scrollView.contentSize.height - 1;
}
// Lock it to offsets that are multiples of 320
yGoto = floorf(offsetY);
if((int)offsetY % 320 > 160){
int dif = ((int)offsetY % 320);
yGoto = offsetY + 320 - dif;
}else{
int dif = ((int)offsetY % 320);
yGoto = offsetY - dif;
}
yGoto = floorf(yGoto); // I keep doing this to take out non integer part
scrollView.decelerationRate = UIScrollViewDecelerationRateFast;
(*targetContentOffset) = CGPointMake(scrollView.contentOffset.x,yGoto);
}
Hope it helps!
I have a UICollectionView with 6 pages, and paging enabled, and a UIPageControl. What I want is, when I came to the last page, if I drag to right, UICollectionView reloads from first page seamlessly.
- (void)scrollViewDidEndDecelerating:(UIScrollView *)sender
{
// The key is repositioning without animation
if (collectionView.contentOffset.x == 0) {
// user is scrolling to the left from image 1 to image 10.
// reposition offset to show image 10 that is on the right in the scroll view
[collectionView scrollRectToVisible:CGRectMake(collectionView.frame.size.width*(pageControl.currentPage-1),0,collectionView.frame.size.width,collectionView.frame.size.height) animated:NO];
}
else if (collectionView.contentOffset.x == 1600) {
// user is scrolling to the right from image 10 to image 1.
// reposition offset to show image 1 that is on the left in the scroll view
[collectionView scrollRectToVisible:CGRectMake(0,0,collectionView.frame.size.width,collectionView.frame.size.height) animated:NO];
}
pageControlUsed = NO;
}
It doesn't work like I want. What can I do?
Here's what I ended up with for my UICollectionView (horizontal scrolling like the UIPickerView):
#implementation UIInfiniteCollectionView
- (void) recenterIfNecessary {
CGPoint currentOffset = [self contentOffset];
CGFloat contentWidth = [self contentSize].width;
// don't just snap to center, since this might be done in the middle of a drag and not aligned. Make sure we account for that offset
CGFloat offset = kCenterOffset - currentOffset.x;
int delta = -round(offset / kCellSize);
CGFloat shift = (offset + delta * kCellSize);
offset += shift;
CGFloat distanceFromCenter = fabs(offset);
// don't always recenter, just if we get too far from the center. Eliza recommends a quarter of the content width
if (distanceFromCenter > (contentWidth / 4.0)) {
self.contentOffset = CGPointMake(kCenterOffset, currentOffset.y);
// move subviews back to make it appear to stay still
for (UIView *subview in self.subviews) {
CGPoint center = subview.center;
center.x += offset;
subview.center = center;
}
// add the offset to the index (unless offset is 0, in which case we'll assume this is the first launch and not a mid-scroll)
if (currentOffset.x > 0) {
int delta = -round(offset / kCellSize);
// MODEL UPDATE GOES HERE
}
}
}
- (void) layoutSubviews { // called at every frame of scrolling
[super layoutSubviews];
[self recenterIfNecessary];
}
#end
Hope this helps someone.
I've been using the Street Scroller sample to create an infinite scroller for images. That works fine until I wanted to set pagingEnabled = YES; Tried tweaking around the recenterIfNecessary code and finally realized that it's the contentOffset.x that has to match the frame of the subview that i want visible when paging stops. This really isn't going to work in recenterIfNecessary since you have no way of knowing it will get called from layoutSubviews. If you do get it adjusted right, the subview may pop out from under your finger. I do the adjustment in scrollViewDidEndDecelerating. So far I haven't had problems with scrolling fast. It will work and simulate paging even when pagingEnabled is NO, but it looks more natural with YES.
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
[super scrollViewDidEndDecelerating:scrollView];
CGPoint currentOffset = [self contentOffset];
// find the subview that is the closest to the currentOffset.
CGFloat closestOriginX = 999999;
UIView *closestView = nil;
for (UIView *v in self.visibleImageViews) {
CGPoint origin = [self.imageContainerView convertPoint:v.frame.origin toView:self];
CGFloat distanceToCurrentOffset = fabs(currentOffset.x - origin.x);
if (distanceToCurrentOffset <= closestOriginX) {
closestView = v;
closestOriginX = distanceToCurrentOffset;
}
}
// found the closest view, now find the correct offset
CGPoint origin = [self.imageContainerView convertPoint:closestView.frame.origin toView:self];
CGPoint center = [self.imageContainerView convertPoint:closestView.center toView:self];
CGFloat offsetX = currentOffset.x - origin.x;
// adjust the centers of the subviews
[UIView animateWithDuration:0.1 animations:^{
for (UIView *v in self.visibleImageViews) {
v.center = [self convertPoint:CGPointMake(v.center.x+offsetX, center.y) toView:self.imageContainerView];
}
}];
}
I have not used UICollectionView for infinite scrolling, but when doing it with a UIScrollView you first adjust your content offset (instead of using scrollRectToVisible) to the location you want. Then, you loop through each subview in your scroller and adjust their coordinates either to the right or left based on the direction the user was scrolling. Finally, if either end is beyond the bounds you want them to be, move them to the far other end. Their is a very good WWDC video from apple about how to do infinite scrolling you can find here: http://developer.apple.com/videos/wwdc/2012/
I'm having difficulties getting a tiled UIScrollView to zoom in and out correctly with pinch zooming. The issue is that when a pinch-zoom occurs, the resulting view is usually not centered in the same region.
Details: The app starts with a tiled image that is 500x500. If a user zooms in, it will snap to 1000x1000 and the tiles will redraw. For all the zoom affects, etc. I am just letting the UIScrollView do it's thing. When scrollViewDidEndZooming:withView:atScale: is called, I redraw the tiles (like you can see in many examples and other questions here).
I think that I've drilled the problem down to calculating the center of the view correctly when I get to scrollViewDidEndZooming:withView:atScale: (I can center on a known point fine after I redraw).
What I'm currently using:
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)scale {
// as an example, create the "target" content size
CGSize newZoomSize = CGSizeMake(1000, 1000);
// get the center point
CGPoint center = [scrollView contentOffset];
center.x += [scrollView frame].width / 2;
center.y += [scrollView frame].height / 2;
// since pinch zoom changes the contentSize of the scroll view, translate this point to
// the "target" size (from the current size)
center = [self translatePoint:center currentSize:[scrollView contentSize] newSize:newZoomSize];
// redraw...
}
/*
Translate the point from one size to another
*/
- (CGPoint)translatePoint:(CGPoint)origin currentSize:(CGSize)currentSize newSize:(CGSize)newSize {
// shortcut if they are equal
if(currentSize.width == newSize.width && currentSize.height == newSize.height){ return origin; }
// translate
origin.x = newSize.width * (origin.x / currentSize.width);
origin.y = newSize.height * (origin.y / currentSize.height);
return origin;
}
Does this seem correct? Is there a better way? Thanks!
The way I have solved this so far is to store the initial center point of the view when the zoom starts. I initially saving this value when the scrollViewDidScroll method is called (and the scroll view is zooming). When scrollViewDidEndZooming:withView:atScale: is called, I use that center point (and reset the saved value).
The center of the scrollview can be found by adding it's center property, and it's contentOffset property.
aView.center = CGPointMake(
self.scrollView.center.x + self.scrollView.contentOffset.x,
self.scrollView.center.y + self.scrollView.contentOffset.y);
I have a UIView inside a UIScrollView. Whenever the UIScrollView zoom changes, I want to redraw the entire UIView at the new zoom level.
In iOS < 3.2, I was doing this by resizing the UIView within the UIScrollView to make it the new size, and then setting the transform back to Identity, so that it wouldn't try to resize it further. However, with iOS >= 3.2, changing the identity also changes the UIScrollView's zoomScale property.
The result is that whenever I zoom (say 2x), I adjust the embedded UIView to be the appropriate size, and redraw it. However now (since I reset the transform to Identity), the UIScrollView thinks its once again at zoomScale 1, rather than zoomScale 2. So if I have my maxZoomScale set at 2, it will still try zooming further, which is wrong.
I thought about using the CATiledLayer, but I don't think this is sufficient for me, since I want to redraw after every zoom, not just at certain zoom thresholds like it tries to do.
Does anyone know how to do the proper redrawing of the UIView on a zoom?
Tom,
Your question is a bit old, but I came up with a solution for this, so I figured I'd put in an answer in case it helps you or anyone else. The basic trick is to reset the scroll view's zoomScale to 1, and then adjust the minimumZoomScale and maximumZoomScale so that the user can still zoom in and out as expected.
In my implementation, I've subclassed UIScrollView and set it to be its own delegate. In my subclass, I implement the two delegate methods you need for zooming (shown below). contentView is a property I added to my UIScrollView subclass that in order to give it the view that actually displays the content.
So, my init method looks something like this (kMinimumZoomScale and kMaximumZoomScale are #define's at the top of the class):
- (id)initWithFrame:(CGRect)frame {
if (self = [super initWithFrame:frame]) {
self.autoresizesSubviews = YES;
self.showsVerticalScrollIndicator = YES;
self.showsHorizontalScrollIndicator = NO;
self.bouncesZoom = YES;
self.alwaysBounceVertical = YES;
self.delegate = self;
self.minimumZoomScale = kMinimumZoomScale;
self.maximumZoomScale = kMaximumZoomScale;
}
return self;
}
Then I implement the standard UIScrollView delegate methods for zooming. My ContentView class has a property called zoomScale that tells it what scale to use for displaying its content. It uses that in its drawRect method to resize the content as appropriate.
- (UIView *)viewForZoomingInScrollView:(UIScrollView *)aScrollView {
return contentView;
}
- (void)scrollViewDidEndZooming:(UIScrollView *)aScrollView withView:(UIView *)view atScale:(float)scale {
CGFloat oldZoomScale = contentView.zoomScale;
CGSize size = self.bounds.size;
// Figure out where the scroll view was centered so that we can
// fix up its offset after adjusting the scaling
CGPoint contentCenter = self.contentOffset;
contentCenter.x += size.width / (oldZoomScale * scale) / 2;
contentCenter.y += size.height / (oldZoomScale * scale) / 2;
CGFloat newZoomScale = scale * oldZoomScale;
newZoomScale = MAX(newZoomScale, kMinimumZoomscale);
newZoomScale = MIN(newZoomScale, kMaximumZoomscale);
// Set the scroll view's zoom scale back to 1 and adjust its minimum and maximum
// to allow the expected amount of zooming.
self.zoomScale = 1.0;
self.minimumZoomScale = kMinimumZoomScale / newZoomScale;
self.maximumZoomScale = kMaximumZoomScale / newZoomScale;
// Tell the contentView about its new scale. My contentView.zoomScale setter method
// calls setNeedsDisplay, but you could also call it here
contentView.zoomScale = newZoomScale;
// My ContentView class overrides sizeThatFits to give its expected size with
// zoomScale taken into account
CGRect newContentSize = [contentView sizeThatFits];
// update the content view's frame and the scroll view's contentSize with the new size
contentView.frame = CGRectMake(0, 0, newContentSize.width, newContentSize.height);
self.contentSize = newContentSize;
// Figure out the new contentOffset so that the contentView doesn't appear to move
CGPoint newContentOffset = CGPointMake(contentCenter.x - size.width / newZoomScale / 2,
contentCenter.y - size.height / newZoomScale / 2);
newContentOffset.x = MIN(newContentOffset.x, newContentSize.width - size.width);
newContentOffset.x = MAX(0, newContentOffset.x);
newContentOffset.y = MIN(newContentOffset.y, newContentSize.height - .size.height);
newContentOffset.y = MAX(0, newContentOffset.y);
[self setContentOffset:newContentOffset animated:NO];
}
In my case, I have an image view and on top of the image view I have several other imageviews. This is the implementation I came up with and works fine:
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(double)scale{
NSLog(#"finished zooming");
NSLog(#"position x :%f",pin1.frame.origin.x);
NSLog(#"position y :%f",pin1.frame.origin.y);
CGRect frame = pin1.frame;
frame.origin.x = pin1.frame.origin.x * scale;
frame.origin.y = pin1.frame.origin.y * scale;
pin1.frame = frame;
NSLog(#"position x new :%f",pin1.frame.origin.x);
NSLog(#"position y new:%f",pin1.frame.origin.y);
}
In my iPhone app I'm looking for a solution where I have some images scrolling horizontally, automatically and infinitely around and around. So if I have four images: first image 1 is shown, then it automatically scrolls out, image 2 is shown, then it scrolls out, ... image 4 is shown, then it scrolls out, and then image 1 is shown again and around it goes... (image1->image2->image3->image4->image1...)
I have been looking for a solution where I use a UIScrollView, but I'm not sure how to implement it. Is there a tutorial or anything on how to do this? How would you solve it? Thanks!
You can implement the ScrollViewDelegate's - (void)scrollViewDidScroll:(UIScrollView *)scrollView method and use the setContentOffset of the scroll view once the content offset is larger than some maximum or less than some minimum.
Before doing that you will have to duplicate the contents of the scroll view at least 3 times, like this: .
Once the scroll offset reaches the duplicated content you will have to set the offset to the original content offset...
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
if (scrollView == self.infiniteScrollView) {
CGFloat xOffset = scrollView.contentOffset.x;
CGFloat yOffset = scrollView.contentOffset.y;
if (xOffset > maxOffset) {
xOffset = origOffset + (xOffset - maxOffset);
}
else if (xOffset < minOffset) {
xOffset = origOffset + (xOffset - minOffset);
}
if (xOffset != scrollView.contentOffset.x) {
[scrollView setContentOffset:CGPointMake(xOffset ,yOffset)];
}
}
}