Currently I encounter an issue somehow, the application lost all those artistic UI animation for example, page flipping, alert view popup, action sheet slide up and etc. That means all those UI will show up immediately without any transition animation. It looked very weird.
Firstly, the app will run smoothly until something trigger the issue above, and after that only re-run the app or kill the app will stop the problem.
There is no error message or any clue that I can figure out what could be the reason. Have any one of you guy has encountered similar issue as above? Please share with me how am I able to solve the issue above. Thanks.
Animations may get disabled for the entire app whenever an attempt is made to animate views on a background thread, e.g. by calling one of UIView's animateWithDuration:animations: family of class methods from a background thread. Be sure to update your app's UI only from the main thread.
You can check if code is running on the main thread by testing [NSThread currentThread].isMainThread and you can ensure it runs on the main thread like so:
dispatch_async(dispatch_get_main_queue(), ^(void) {
// Your code
});
Alternatively, ensure that you're not calling [UIView setAnimationsEnabled:NO] anywhere, as that will also disable animations for the entire app.
Related
I am created an app, after login have to download new database from web and when you logged
in a custom UIAlertView appears if user press yes the download phase will be started. When
the UIAlertView disappear and the UIAlertView's delegate called i start on the background
thread a download. Now i am trying to modify a label which display the current percent and
adding to the view a custom activity indicator. After that when the activity indicator
changing the pictures or the label.text get a new string the screen start flickering, but
only at the very first start (after install), if i force close the app and starting it
again the flicker thing is not appearing, on previous version of iOS the app not flicker. I
am calling from main thread when i modify the label. I tried remove label and activity
indicator and after the alert view disappearing the app not flicker. I tried to remove
alert view and start instantly the download and after that only the status bar started to
flicker.
So my question: what should i do to solve the flicker bug?
I believe that the reason is because you are updating the UI on a background thread. You must not do this, you must use the main thread for this:
To run code on the main thread from the background thread, you can use GCD:
dispatch_async(dispatch_get_main_queue(), ^{
//your UI code here
});
If this doesn't fix the error, it's probably a bug with your device.
I load image by NSOparationInvokation and call out method in the main thread, which adds this image to scroll view, but app hardly lags. If I load image but not add it view, app works normally, if I add test button on view app also work normally and if I load image and add test button to view app don't lag. By profiler problem in __spin_lock. Someone knows what's wrong?
Thanks.
When using threads on iOS, you should never ever ever make calls to UIKit. That's why it won't load. Put it on the main thread and it'll work.
I have a UIView following the users finger as they move it around inside my app. Sometimes, other things on screen are animating with UIViewAnimation blocks, but this freezes the tracking of their finger, so if they continue moving their finger during the animation, it won't follow. How can i stop the animation from blocking up the main thread?
Try using UIViewAnimationOptionAllowUserInteraction with [UIView animateWithDuration:delay:options:animations:completion:]
you can use the NSObject's method: performSelector:onThread:withObject:waitUntilDone:
More details in Apple NSObject Documentation
If there is any other thing on the screen is animated, that would also be done in main thread. And the current finger tracking would also be done in main thread. So definitely there would be some blocking.
To get rid of that, we can optimize our code using blocks and GCD.
Note that if you link for iOS 5 this problem will go away all by itself. Under iOS 5, block-based animation of a view does not turn off user interaction for other views. This is what Apple should have done in the first place.
I've made a custom activity indicator (actually just an imageView)
When user clicks something and I expect it will take a bit long to process(alloc a UIViewController and push on to navigation stack),
I alloc the indicator and add it as subview of current view just before the lengthy process starts.
Strange thing is, indicator doesn't show up until the push (left-right) animation starts.
Is it because the lengthy job takes the system, and ui drawing for activity indicator is delayed?
Am I doing something wrong here?
Thank you
Edit
Looks like I can do the "push" in background.. i'm trying it now
IPhone SDK - Leaking Memory with performSelectorInBackground
Is your job synchrone or asynchrone ?
If it's the first case, then it can be the problem.
Check all the method like :
[ self performSelector:<#(SEL)aSelector#> ];
You can thread this to avoid your [potential] problem.
Good luck.
You should process your lengthy tasks in the background. The UI won't update if you block the main thread.
So you have to refactor your app, the alloc and push of the viewController should happen within the blink of an eye, because you can't do this in the background.
But you can do the processing (downloading data I guess) in the background.
There is plenty information available about background processing. The way to go varies heavily on what you want to do exactly.
Does someone know of a way, or has a creative idea as to how to obtain an UIImage that is rendered from a UIWebView? The catch is, that is must be on a background thread.
I'll elaborate:
I'm trying to obtain the image from multiple UIWebViews every second+-, and display it on screen (iPhone's of course). Because rendering a layer to a CGContext is a CPU consuming job, I wouldn't like to use the main thread, so not to hang the UI.
My attempts so far were:
I tried to use renderInContext on the webView's layer to the UIGraphicalContext, but the _WebTryThreadLock error crashed the webviews.
I tried creating a CGBitmapContext, and render the webview's layer to it, but got the same result.
I tried implementing a copy method (by adding a Category) to CALayer, that deep copied all of the public properties, and sublayers. Afterwards, I tried to renderInContext the layer I copied. I got a UIImage that was partially "correct" - meaning, not all of the layers were rendered, so for example, i would get only the website header (or footer, or body, or search bar, or just a some of the frames). The UIWebview's layer consists of all sort of subclassed CALayers, so this is probably why this approached didn't work.
I tried setting the kCATransactionDisableActions in a CATransaction, but it didn't appear to change this behavior (neither of them).
I'm pretty close to giving up.
Is there a savior among you people?
UIWebView hates, and I mean really hates, having anything done to it on a background thread. UIKit is not fully thread safe. Drawing to a graphics context is (this was added in iOS 4), but not creating UIViews on a secondary thread.
Are you creating your UIWebViews off the main thread? Do you perhaps have some code to share? I would suspect your issues are being caused by the fact you're trying to perform operations to a UIWebView on a secondary thread. The drawing operation to render the view's contents as an image can happen off the main thread, but creating the view itself can't.
I've been working on this, too.
In a thread I create a view hierarchy, loop until the web-view has finished loading content.
The webview I create is inside of a UIViewController's viewdidload-- I've tried doing
if ([NSThread isMainThread] == NO) {[self performselectorOnMainThread: #selector(viewDidLoad)return;)}
And I've done the same for dealloc'ing the webView.
But that didn't work.. I've only found that we avoid UIWebView exceptions UNTIL we hit the autorelease pool...
I'm using instruments to figure out why.
Here's my attack strategy...
I'm going to perform the render operation on the main thread with an off-screen view, having a separate thread running some sort of queue to manage them. I'm worried about UI lag, so it'll have to be fairly efficient.