I have a question regarding view hierarchy:
I currently have a HomeViewController that is loaded into view after a login screen. The HomeViewController has a ContainerView, which is embedded with a SubViewController. This container is initially hidden when the home view is loaded. When I trigger an action (via a UIButton) to "unhide" the container, I am trying to have an image load in that SubViewController that was rendered in the HomeViewController during viewDidLoad.
The problem I am facing is that for whatever reason, I can not seem to have the image display in the SubViewController.
FYI: The way I am rendering this image is such:
Upon the HomeViewController's viewDidLoad, I am taking a screen shot programmatically of a UIView that is generated from saved user data. This UIView is displayed in the view of the HomeViewController.
When the user clicks a button, I am unhiding and now showing the SubViewController, the view embedded in the ContainerView.
I can not seem to get the screen shot image (saved as imageSS) to appear in the SubViewController. I have tried to suppress the viewDidLoad method for the SubViewController when the HomeViewController is loaded, then call the SubViewController viewDidLoad when the button is pressed to show it, but no luck there either.
This might be confusing but it should be easy - I am at a loss why I can't get this to work. If anyone can help me out I would appreciate it. Thanks!
Here is the code i am currently trying: this method is in the HomeViewController.m
- (void)takeScreenshot:(id)sender {
UIGraphicsBeginImageContextWithOptions(_homeRenderImage.bounds.size, NO, 0.0);
[_homeRenderImage drawViewHierarchyInRect:_homeRenderImage.bounds afterScreenUpdates:YES];
UIImage *imageSS = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
SubViewController *pvc = [[SubViewController alloc] init];
userImage = imageSS;
[pvc loadImage];
}
Here is the method I am using in the SubViewController.m:
NOTE: userImage is a shared property between these controllers. I have tested that this sharing works
- (void)loadImage {
_subImage.image = userImage;
}
I feel dumb - all I needed to do was to call the loadImage method in the viewWillAppear method:
- (void)viewWillAppear:(BOOL)animated{
[super viewWillAppear: animated];
[self loadImage];
}
Related
I have two view controllers in Xcode project (all view controllers are created in storyboard).
First view controller has two (or more) buttons with certain background images. Second view controller should display full-screen background image of certain button after user touch it (certain button).
Second view controller has a property UIImageView that should be allocated and initialized in the code of second view controller (UIImageView not created in storyboard).
Second view controller is a delegate for first view controller and has a method:
-(void) viewController:(ViewController *) viewController buttonPressed: (UIButton *) button.
Every button has a modal segue to second view controller.
So the sequence of actions of application is next (I realized that by debugging):
User touches any button
Button calls an action method in which delegate method viewController:buttonpressed: is called. UIImageView instance is allocated and initialized in this method with the image returned by button backgroundImageForState:
Than method viewDidLoad of second view controller is called, in which UIImageView instance should be added to super view of second view controller and displayed on screen.
The problem is that despite of allocation of UIImageView instance in delegate method viewController:buttonpressed:, that instance is become nil at the start of method viewDidLoad of second view controller. All actions that been made in viewController:buttonpressed: became unavailing.
The code is below:
First View Controller Code
- (void)viewDidLoad {
[super viewDidLoad];
ViewControllerForImage *temp = (ViewControllerForImage *) [self.storyboard instantiateViewControllerWithIdentifier:#"ViewControlForImage"];
self.delegate = temp;
}
-(IBAction)buttonPressed:(id)sender{
[self.delegate viewController:self buttonPressed:sender];
}
Second View Controller Code
#synthesize myImage;
- (void)viewDidLoad {
[super viewDidLoad];
[self.view addSubview:myImage];
}
-(void) viewController:(ViewController *) viewController buttonPressed: (UIButton *) button{
myImage = [[UIImageView alloc] initWithImage:[button backgroundImageForState: UIControlStateNormal]];
[myImage setFrame:CGRectMake(0, 0, 320, 504)];
}
Why don't you just pass the information in a prepareForSegueMethod?
Also in your code why are you sending an instance of viewcontroller back to the second view controller? You are not using it at all.
I am pushing self view to self.navigationcontroller by allocating. I have a tableView on that view so I am changing the content of tableview. But when I am pressing back button (that is automatically created), I am not able to show previous content. Its showing updated content.
Please suggest.
You set code in viewWillAppear method
- (void)viewWillAppear:(BOOL)animated
{
//code set here
}
If you fill the tableView's data in viewWillAppear: or viewDidAppear:, it will reload even if you only press the back button of your top viewController. If you do not want to have your content changed, you are supposed to use initWithNibName: or viewDidLoad: methoads. They are called only at creation time of the view.
Based on the comments on #Kirti's post, You can check if your viewcontroller is being popped by following method, and take some necessary actions for you controller holding table.
-(void) viewWillDisappear:(BOOL)animated
{
if(![self.navigationController.viewControllers containsObject:self])
{
YourControllerWithTable *instance = [self.navigationController.viewControllers objectAtIndex:self.navigationController.viewControllers.count - 1];
instance.loadOldContent = YES;
}
}
In viewWillAppear: of YourControllerWithTable, you can check:
-(void) viewWillAppear:(BOOL)animated
{
if(loadOldContent)
{
//Do your work here
}
}
You don't push UIView instances onto a UINavigationController instance, only instances of UIViewController.
As part of my updating my apps to replace the deprecated presentModalViewController with presentViewController, I did some testing.
What I found was disturbing. Whereas presentModalViewController always works and there is no question about it working, I have found the presentViewController method often will not display my VC at all. There is no animation and it never shows up.
My loadView are called without problems, but the actual view does not appear.
So here is what I am doing:
User taps a button in my main view controller.
In the callback for that tap, I create a new view controller and display it as shown above.
The VC never appears (it is an intermittent problem though) but because this VC begins playing some audio, I know that its loadView was called, which looks like as follows.
My button-pressed callback is as follows:
- (void) buttonTapped: (id) sender {
VC *vc = [[VC alloc] init];
[self presentViewController: vc animated:YES completion: nil];
[vc release];
}
Here is my loadview in the VC class:
- (void) loadView {
UIView *v = [UIView new];
self.view = v;
[v release];
... create and addsubview various buttons etc here ...
}
Thanks.
Make sure the controller that calls the function has its view currently displayed (or is a parent to the one currently displayed) and it should work.
I am trying to get a popup effect and want to design the popup view in another view controller so i can use the xib to do it.
When i used the presentViewController or pushViewController and set the background to transparent, i end up seeing the Window's background color.
I tried this code to add subview to the navigation controller's view so that i can have the Info view cover the entire screen with a transparent background. I also have tab bar to cover up as well.
InfoVC *vc = [[InfoVC alloc] initWithNibName:#"InfoVC" bundle:nil];
[self.navigationController.view addSubview:vc.view];
My problem is inside my InfoVC when i try to dismiss it, the app will crash with some EXC_BAD_ACCESS message:
[self.view removeFromSuperview];
EDIT:
I found a way to stop it crashing but setting the InfoVC as a property in the MainVC. I think the reason for crash is when i call "self.view" in the action inside the InfoVC, it doesn't know that self is the InfoVC inside MainVC.
InfoVC *vc = [[InfoVC alloc] initWithNibName:#"InfoVC" bundle:nil];
[self.navigationController.view addSubview:vc.view];
No no no no. Never never do that.
There is an elaborate dance that you must traverse in order to put a view controller's view inside another view controller's view (or remove it afterwards) if it doesn't come with built-in facilities for doing this (the way a UISplitViewController does, or the way a navigation controller manages the views of the view controllers that are pushed and popped within it).
Read up on customer container controllers. One of the examples from my book is here:
https://github.com/mattneub/Programming-iOS-Book-Examples/blob/master/ch19p556containerController/p476containerController/ViewController.m
Shouldn't you be using the following to remove the view from its superview?
[vc.view removeFromSuperview];
You can never have a UIView remove it's subviews, the subviews themselves must remove themselves from it's superview. You can easily loop through subviews and have them removed like so
for (UIView *view in vc.view.subviews) {
[view removeFromSuperview];
}
Docs for reference:
http://developer.apple.com/library/ios/#documentation/uikit/reference/uiview_class/uiview/uiview.html
After a "modally" presented view controller has appeared the views under the now presented view controller will be removed; this saves memory, and eases rendering. In your case, though, you also end up seeing the window behind the "modally" presented view.
The natural, and seemingly logical, next step is to simply take one view controller's view and cram it into another. However, as you have discovered, this is problematic. With the newly inserted view safely retained by the view hierarchy it is safe, but the new view controller is not so lucky, it is quickly deallocated. So when this new view tries to contact its controller you will get an EXC_BAD_ACCESS and crash. One workaround, again as you have found, is to simply have the original view controller keep a strong reference to the new view controller. And this can work... badly. There's still a good chance you will get an UIViewControllerHierarchyInconsistencyException.
Of course if you simply want to add a small view you create in IB you don't need to use a view controller as the "File's Owner" and there are many examples of creating an instance of a view from a xib file.
The more interesting question here is, "How would/does apple do it?" Apple consistently says that a view controller is the correct controller for an encapsulated unit of work. For example, their TWTweetComposeViewController, you present it, and it seems to float. How?
The first way of accomplishing this that comes to my mind is to have a clear background that isn't clear. That is, create an image of the screen before the presented view controller appears and set that as the background before the presenting view is removed. So for example(Explanation to follow):
QuickSheetViewController.xib
QuickSheetViewController.h
#import <UIKit/UIKit.h>
#interface QuickSheetViewController : UIViewController
- (IBAction)dismissButtonPressed:(id)sender;
#end
QuickSheetViewController.m
#import "QuickSheetViewController.h"
#import <QuartzCore/QuartzCore.h>
#implementation QuickSheetViewController {
UIImage *_backgroundImage;
}
-(void)renderAndSaveBackgroundImageFromVC:(UIViewController *)vc{
UIGraphicsBeginImageContext(vc.view.bounds.size);
[vc.view.layer renderInContext:UIGraphicsGetCurrentContext()];
_backgroundImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
}
-(void)viewWillAppear:(BOOL)animated{
[super viewWillAppear:animated];
// save an image of the current view, and set our background to clear so we can see the slide-in.
[self renderAndSaveBackgroundImageFromVC:self.presentingViewController];
self.view.backgroundColor = [UIColor clearColor];
}
-(void)viewDidAppear:(BOOL)animated{
[super viewDidAppear:animated];
// Time to use our saved background image.
self.view.backgroundColor = [UIColor colorWithPatternImage:_backgroundImage];
}
-(void)viewWillDisappear:(BOOL)animated{
[super viewWillDisappear:animated];
// Set our background to clear so we can see the slide-out.
self.view.backgroundColor = [UIColor clearColor];
}
- (IBAction)dismissButtonPressed:(id)sender {
[self dismissViewControllerAnimated:YES completion:nil];
}
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation{
return (interfaceOrientation == UIInterfaceOrientationPortrait);
}
#end
The majority of this example hinges upon the renderAndSaveBackgroundImageFromVC: method. In which, we create a graphics context render the view we are about to cover into it, and then create a UIImage to later (in viewDidAppear) use as a background.
Now simply use it like:
QuickSheetViewController *newVC = [[QuickSheetViewController alloc] initWithNibName:nil bundle:nil];
[self presentViewController:newVC animated:YES completion:nil];
You will see through the background just long enough for the animation to happen, then we use our saved image to hide the removal of the presenting view.
I'm pretty new to iOS development, and I'm trying to develop a simple app in which a button changes the subviews. I have a base RootViewController, which displays MiddleView correctly on init. MiddleView has a single button, labeled "First," which is connected (in Interface Builder) to RootViewController's -openFirstView.
Here's how MiddleView is displayed within RootViewController's -viewDidLoad
MiddleViewController *middleTemp = [[MiddleViewController alloc] initWithNibName:#"MiddleView" bundle:nil];
self.middle = middleTemp;
self.middle.rootViewController = self;
[self.view addSubview:middle.view];
[middleTemp release];
So I have the following ViewControllerss: MiddleViewController and FirstController which control MiddleView and FirstView respectively, and a RootViewController which switches between the two.
I've linked this by placing a RootViewController reference in MiddleViewController, and adding
self.middle.rootViewController = self;
to RootViewController's -viewDidLoad.
-(IBAction)openFirstView:(id)sender{
[middle.view removeFromSuperview];
[self.view addSubview:firstController.view];
}
Note: I've tried initializing firstController within -openFirstView, and when it initially didn't run, I moved the initialization to -viewDidLoad and have proven that it is initializing from the nib correctly by displaying FirstView directly in -viewDidLoad
Where firstController is loaded to a reference earlier in code. However, when I run the code and click the button, nothing in the view changes.
I've done some more diagnosing. I've found specifically that -ViewDidLoad in rootViewController is being called twice, once on the original load and once on the first click of the button, and I'm not sure exactly why.
It seems you haven't inialize your firstView in the below method
-(IBAction)openFirstView:(id)sender{
[middle.view removeFromSuperview];
//First initialize the firstController
[self.view addSubview:firstController.view];
}