uikit

问题 In my OpenGL-ES 1.1 based app, I'm using CALayer s as a source for OpenGL textures. Those CALayer s comprise of CGImage s and text rendered through CoreGraphics. Another OpenGL texture source is a screenshot of a UIView taken using -[CALAyer renderInContext:] and UIGraphicsGetImageFromCurrentImageContext . Currently, I'm running completely on the main thread. The latter case in particular is pretty bad because it halts the OpenGL rendering for the whole time it takes to create the UIView and

问题 I have a project that has to be deployed to 4.0 but has some features that are 5.0 only, such as UI customization. I want my UIPopoverBackgroundView subclass to be weak linked, but I always get the following error when launching on 4.X devices dyld: Symbol not found: _OBJC_CLASS_$_UIPopoverBackgroundView I can't use the NS_CLASS_AVAILABLE macro since my custom Background of the popover is a subclass of the UIPopoverBackgroundView class, so it has to be declared in a .h . How can I weak link

问题 I need to draw text on a background thread to save it as an image. I'm doing UIGraphicsPushContext() [NSString drawInRect:] UIGraphicsPopContext() The code works fine, but sometimes it crashes in drawInRect when I'm also drawing on the main thread at the same time. I tried to use NSAttributedString as suggested here: UIStringDrawing methods don't seem to be thread safe in iOS 6. But [NSAttributedString drawInRect:] doesn't seem to render anything on my background thread for some reason. Main

问题 I'm having an issue, I have a simple UICollectionView with a static 200 cells that load images from Flickr. my CellForItemAtIndexPath looks like this: - (UICollectionViewCell *)collectionView:(UICollectionView *)cv cellForItemAtIndexPath:(NSIndexPath *)indexPath { UICollectionViewCell *cell = [cv dequeueReusableCellWithReuseIdentifier:@"FlickrCell" forIndexPath:indexPath]; cell.backgroundColor = [self generateRandomUIColor]; if(![[cell.subviews objectAtIndex:0] isKindOfClass:[PFImageView

问题 Is there a way to overlap 2 or more UIViews with differing background colors and alphas to give the appearance of another color? For example place a red UIView on top of a blue UIView to give the appearance of a single magenta UIView . 回答1: On iOS the only blending mode for views if the so-called "source over" mode. Basically RGB_result = RGB_back * (1 - Alpha_front) + RGB_front * Alpha_front Thus a red (1, 0, 0) view with 0.5 alpha on top of a blue (0, 0, 1) view will result in dark magenta

问题 I am receiving crash reports that appear to be from a UIView animation calling a delegate that has been dealloced. Thread 0 Crashed: 0 libobjc.A.dylib 0x334776f6 objc_msgSend + 18 1 UIKit 0x31c566c4 -[UIViewAnimationState sendDelegateAnimationDidStop:finished:] 2 UIKit 0x31c565d2 -[UIViewAnimationState animationDidStop:finished:] 3 QuartzCore 0x30045a26 run_animation_callbacks I am setting the current view controller as the delegate for animations using the following pattern: [UIView

问题 I am receiving crash reports that appear to be from a UIView animation calling a delegate that has been dealloced. Thread 0 Crashed: 0 libobjc.A.dylib 0x334776f6 objc_msgSend + 18 1 UIKit 0x31c566c4 -[UIViewAnimationState sendDelegateAnimationDidStop:finished:] 2 UIKit 0x31c565d2 -[UIViewAnimationState animationDidStop:finished:] 3 QuartzCore 0x30045a26 run_animation_callbacks I am setting the current view controller as the delegate for animations using the following pattern: [UIView

问题 For some reason, I'm having trouble with making a textfield the first responder. I have a UITableView with two rows. Each row has a label and a UITextField. The textfields are tagged kLoginRowIndex = 0 and kPasswordRowIndex = 1. As you might have guessed, I use this for setting login and password. If the user taps on the return button when editing the login textfield, I want the password textfield to get the focus. Unfortunately, the password textfield doesn't accept the focus. Here is my

问题 For some reason, I'm having trouble with making a textfield the first responder. I have a UITableView with two rows. Each row has a label and a UITextField. The textfields are tagged kLoginRowIndex = 0 and kPasswordRowIndex = 1. As you might have guessed, I use this for setting login and password. If the user taps on the return button when editing the login textfield, I want the password textfield to get the focus. Unfortunately, the password textfield doesn't accept the focus. Here is my

问题 Can a Cocoahead please explain why UIView and it's sub classes don't adopt the NSCopying Protocol? I can see, philosophically, why UITouch would not be copy compliant, as it's a very temporal object. By UIView, and it's subclasses, especially UIButton, seem like they should be able to be copied. Certainly Apple has good reasons for doing things the way they do. Do you know their reason? 回答1: It would seem the question they asked wasn't "Why not?" but "Why do it?" There's little point to doing