I remember that when I was reading the Apple documentation, it would mention that when you call a function such as addSubview, you are adding a “layer of paint,” so to speak, and every time it is called, another layer is overlaid.
This should be an easy question to answer, but I had a hard time thinking of keywords to google for, so please excuse the asking of such a simple question.
How do I clear the “layers” of a custom UIView?
My situation, as it may be relevant: I have these “user cards” that are displayed on the screen. They are initialized with some user images. The cards stay the same, but I call a method in my custom UIView (the card UIView) to redraw the images when I want to display a different user. The problem is that some elements of this custom UIView are transparent, and redrawing these images each time builds on that transparency (an obvious problem).
In Core Graphics, what you draw is what gets shown. The painter’s analogy only refers to a single frame. So if you’re using drawRect, you just don’t cache the previous drawing.
But I suspect you’re talking about some UIKit stuff where you’ve added subviews or sublayers. This will remove those leftover views if you just want to clear everything:
for (UIView *view in customView) {
[view removeFromSuperview];
}
for (CALayer *layer in customView.layer) {
[layer removeFromSuperlayer];
}
Ryan's code for clearing UIViews is more or less correct, but if you came here from Google looking for how to clear CLLayers from a view, I was getting a crash when I attempted to fast enumerate customView.layer like Ryan has in his example.
When I switched it to regular enumeration, it worked for me. Here's a code snippet:
for (int i = 0; i > yourView.layer.sublayers.count; i++) {
CALayer *layer = [self.yourView.layer.sublayers objectAtIndex:i];
[layer removeFromSuperlayer];
}
Related
In my application, I have got a scrollview, a bigger one with lots of subviews on it, subviews gets added dynamically based on scroll. I try to add subviews (imageviews) dynamically on scroll and when user scrolls then I try to fetch more images asynchronously based on pageSize etc from server and these images gets placed into it's corresponding imageview..
I have gone through Apple's WWDC Sessoion 104 as well which appears to be good for offline images.
I also try to resize the images on my scrollview in a ratio, which is fine I believe. The problem is When the number of images increases on the scrollview then application runs out of memory. It must be due to me using the images directly in an imageview instead of using CATiledLayer. But, I am looking for help in displaying async images on scrollview using CATiledLayer.
Many Thanks,
Reno Jones
I edit completely the answer based on the comments.
You should set a controller as delegate of the scrollview than in the scrollViewDidScroll: (or in scrollViewDidEndDecelerating: if you want to check it less often) method you can check if some your images are outside the visible part of the content view and then release (i.e. set the pointer to nil) them to save some memory.
For your convenience here's an example how to get the visible part of your content:
CGRect visibleRect;
visibleRect.origin = scrollView.contentOffset;
visibleRect.size = scrollView.bounds.size;
everything completely outside this rect should be released (of course you then have to reload them if user scroll: it may be tricky constantly load/unload...)
This in simple words is all I did.. I have already been downloading images async and caching them up on device, then I have added an UIImage (imageObject) property to my current tile class, which holds the image object being downloaded and then implemented the following and did the trick for me. And believe me or not, imageview loading vs CATiledLayer - CATiledLayer is 100x faster and efficient.
+ layerClass
{
return [CATiledLayer class];
}
- (void)drawRect:(CGRect)rect
{
[imgObject drawAtPoint:CGPointMake(0,0)];
}
Hope it helps someone else in future. Let me know if I can be of more help.
I have a EAGLView that I wish to convert into a UIImage. I can do this with the solution posted here:
How to get UIImage from EAGLView?
However, I can only accomplish this if a small amount of time has gone by between the creation of the EAGLView and the UIImage.
This code, which creates a EAGLView, and then a UIImageView right afterwards, does not work:
EAGLView *EAGLphoto = [[EAGLView alloc] initWithImage:photo.workAreaImage];
[theWorkArea.photoArea1 addSubview:EAGLphoto];
//I put a glfinish() here but it didn't help
UIImageView *photoView = [[UIImageView alloc] initWithImage:[self glToUIImage]];
//glToUIImage is taken from the link above
[theWorkArea.photoArea2 addSubview:photoView];
I'm assuming the UIImageView tries to get created before the EAGLView is finished being created. I tried to put a glfinish() in between but it did nothing. When I run the code, the EAGLView shows up fine but the UIImageView shows up as black.
However, this modified version of the above code works:
EAGLView *EAGLphoto = [[EAGLView alloc] initWithImage:photo.workAreaImage];
[theWorkArea.photoArea1 addSubview:EAGLphoto];
[self performSelector:#selector(getUIImage) withObject:nil afterDelay:0.1];
- (void)getUIImage {
UIImageView *photoView = [[UIImageView alloc] initWithImage:[self glToUIImage]];
//glToUIImage is taken from the link above
[theWorkArea.photoArea2 addSubview:photoView];
}
Am I using glfinish() incorrectly? Is there a better method than my hack?
Usually when you make visible changes to UIKit objects instead of updating instantly they merely flag themselves to make those changes in the future, then do the whole set of changes as a batch next time you relinquish the main thread (by returning to the runloop). That's not a misfeature or a failure in the implementation, it's actually usually what you implicitly expect, being the reason you can write code like:
view.frame = someNewFrame;
view.someOtherProperty = someOtherValue;
And not worry that every so often the view will visibly adopt the new frame before adopting the other changes. As a rule, you want the things you do to views to appear to be atomic.
Occasionally you run into a situation, as you have here, where the fact that changes you've already requested haven't come into effect yet is exposed. frame and someOtherProperty would return their new values in the above example so that you don't care whether the changes took effect immediately or not, but based on your observation about performSelector:withObject:afterDelay: it seems likely that you've stumbled upon a situation where the change doesn't pretend to be immediate.
EAGLView is difficult to diagnose because it's not really a UIKit feature. The CAEAGLLayer that it's built upon is, but EAGLView is just the name Apple have adopted for a custom UIView subclass built on CAEAGLLayer in various example projects. They've not been consistent about the interface or implementation of EAGLView across their examples, but at a guess I'd say that probably it's creating the OpenGL frame buffer object (that is, the thing that OpenGL uses to store numbers related to pixels, allowing glReadPixels to work) only when asked to lay itself out, and it doesn't lay itself out until UIKit asks it to do so. Which isn't until you've dropped out to the runloop.
That diagnosis can be confirmed by checking the code of the EAGLView that you have. If there are a bunch of calls to things like glGenFramebuffers that are triggered as a result of layoutSubviews, drawRect or some other method that isn't called directly by the relevant init then that proves it.
Assuming that diagnosis to be correct, you could adapt EAGLView but I think probably the best solution is just to stick to performSelector:withObject:afterDelay:0. This isn't a race condition, so that solution isn't in the slightest bit flakey or unreliable, it's just a slightly roundabout way of saying "let UIKit catch up with all of those instructions, given that I know that'll let EAGLView get into a meaningful state, then continue with my stuff".
I have a UIView with a bunch of subviews, all positioned using layoutSubviews. When the view is resized, the relative positions all change. I'd like these re-calculations to happen during an animated resize (using +[UIView beginAnimations:] calls). This doesn't seem to be happening. Any ideas?
Assumption: You want to have multiple animation steps (i.e. position doesn't change linearly with frame size).
This isn't possible with a single "standard" UIView animations. Why? The frame/bounds is only set once.
Core Animation has three "layer trees":
The model tree is where your app thinks things are.
The presentation tree is approximately what's being displayed on screen.
The render tree is approximately what Core Animation is compositing.
UIView is a (somewhat thin) wrapper around the model layer. During a UIView animation, Core Animation updates the presentation/render tree — the model tree represents the endpoint of animations. The upshot is that your code can (for the most part) treat animations as instantaneous — moving a view from A to B instantly moves it to B; the change just happens to be animated to the user.
There are more complicated things you can do with CALayer/CAAnimation directly, but I haven't investigated this much.
You could chain multiple animations together using -[UIView setAnimationDidStopSelector:]. (You could also try using multiple animations together with setAnimationDelay:, but I'm not sure what happens with multiple animations on the same property; you might have luck with setAnimationBeginsFromCurrentState:.)
If you want really fine-grained control, CADisplayLink (OS 3.1+) is a timer that fires after each screen refresh. A fallback option (for 3.0 support) is to use an NSTimer at 30/60 Hz or so.
I know this is an old question, but this code works for me very well (suited for your example of changing frame).
-(void)layoutSubviews{
[super layoutSubviews];
// layout your subviews here, or whatever
}
-(void)someMethod{
double duration=...;
[UIView animateWithDuration:duration animations:^{
self.frame = ...;
[self layoutIfNeeded];
}];
}
Of course you can call this method from another object. The "trick" is to call layoutIfNeeded (or layoutSubviews directly - same thing, if You change the frame the setNeedsLayout is called).
As tc. nicely explained the "layer trees", You just force the presentation layer to display the final stage of model layer with animation.
The advantage of this method is in possibility to control when the frame/bounds change is animated and when it's instant.
Hope this helps someone:).
Completing #GrizzlyNetch's anwer, you can set the UIViewAnimationOptionLayoutSubviews animation option, so you don't need to call layoutIfNeeded:
-(void)someMethod{
double duration = ...;
[UIView animateWithDuration:duration delay:0 options:UIViewAnimationOptionLayoutSubviews animations:^{
self.frame = ...;
} completion:nil];
}
Posting for completeness. Thanks to tc. for explaining that what I want to do, exactly, is not supported by Core Animation.
I eventually came up with a reasonable solution. Rather then layout my subviews in -layoutSubviews, I do so in -setBounds:. Then, when I wrap a -setBounds: call in a UIView +beginAnimations: block, those positioning calls are also animated, and the end result is everything properly animating to where it should god.
I'd like help on some strategies to sequence some animations.
I subclassed UIImageView so that I could write some custom animation actions on an image. I implemented a few methods to be used as actions that I could call on my image
example:
-(void)rotateAnim; //rotates the image by a few degrees using a CGAffine Transform
-(void)numbersFlashAnim; //uses the UIImageVew.animationImages array for a 14 frame animation.
-(void)moveLeftAnim; //uses another CGAffine Transform to change the imageView's position.
In my viewDidLoad method I create an instance of my UIImageView subclass. What ways exist to call these animations in sequence?
I was thinking about using an NSTimer to handle the animations, but wasn't sure if you could write an NSTimer object to handle multiple method calls.
example:
[imageView rotateAnim]; //when this animation is done, I want to call:
[imageView numbersFlashAnim];
I've seen several questions regarding the use of an NSTimer, but none that specifically relate to this problem. Note: I saw that the dev docs on apple's site also recommend the use of the performSelector:withObject:afterDelay: in some cases but was wondering if that would offer enough flexibility.
Additionally, I've already taken a look at the Cocos2d framework, and although I can use their methods ~(Sequence actions: etc, ) I'm choosing to solve this problem with UIKit/Foundation, etc.
Do you use animation? I mean you can rotate your image inside
[UIView beginAnimations:(NSString *)animationID context:(void *)context] block. There you can add a delegate method that will be called after current animation ends. And there you can call your numbersFlashAnim.
(Sorry for my english ;-) )
I'm trying to create a custom transition, to serve as a replacement for a default transition you would get here, for example:
[self.navigationController pushViewController:someController animated:YES];
I have prepared an OpenGL-based view that performs an effect on some static texture mapped to a plane (let's say it's a copy of the flip effect in Core Animation). What I don't know how to do is:
grab current view content and make a texture out of it (I remember seeing a function that does just that, but can't find it)
how to do the same for the view that is currently offscreen and is going to replace current view
are there some APIs I can hook to in order to make my transition class as native as possible (make it a kind of Core Animation effect)?
Any thoughts or links are greatly appreciated!
UPDATE
Jeffrey Forbes's answer works great as a solution to capture the content of a view.
What I haven't figured out yet is how to capture the content of the view I want to transition to, which should be invisible until the transition is done.
Also, which method should I use to present the OpenGL view?
For demonstration purposes I used pushViewController. That affects the navbar, though, which I actually want to go one item back, with animation, check this vid for explanation:
http://vimeo.com/4649397.
Another option would be to go with presentViewController, but that shows fullscreen.
Do you think maybe creating another window (or view?) could be useful?
While I cannot completely answer your question without doing some more research of my own, I can help a bit:
-In order to get the view of a UINavigationController, you need to take a screenshot. The easiest way to do this is by grabbing it into a UIImage:
UIGraphicsBeginImageContext(self.view.frame.size);
[[self.view layer] renderInContext:UIGraphicsGetCurrentContext()];
UIImage* test = UIGraphicsGetImageFromCurrentImageContext();
UIImageView* view = [[UIImageView alloc] initWithImage:test];
UIGraphicsEndImageContext();
I am not sure if you can render a GLContext (not familiar on the phone) into a CGImage, but I would do something like that (and init a UIImage from that). I would prerender every frame of the animation you are trying to do and slap it into an UIImageView using the animation stuff provided within. That is, if your animation is simple enough. Otherwise, it might come down to writing your own animation function :-/
I have just put together a transition class to implement your own transition animation in OpenGL ES.
Feel free to read about it here
There are two example transitions in the project, feel free to add you own to it.
I think the function you might be thinking of is http://www.opengl.org/sdk/docs/man/xhtml/glCopyTexImage2D.xml ... you set the viewport to the texture size and then draw as usual, then do glCopyTexImage2D to copy the scene onto a texture.
or you should look into FrameBuffer Objects. The default OpenGL template in XCode uses these. Just generate the example project to see how those work.
I recently write some transitioning animation betweeen view controllers like you. If you want to get any extra info from the invisible view, you can try delaying the transition like this :
- (void)animationFromModalView:(UIView *)modalView toMasterView:(UIView *)masterView
{
[masterView setNeedsLayout];
[masterView layoutIfNeeded];
[self performSelector:#selector(delayAnimationFromModalViewToMasterView) withObject:nil afterDelay:.1f];
}