I have a pretty simple UIViewController. It's initialized with a view I've created in Interaface Builder, which contains only a UIImageView. When the user touches the screen, I want the touchesBegan message of UIViewController to get called. So, I override it and added some logging, but nothing has happened.
I haven't done anything "special" at all, as since UIViewController inherits from UIResponder, I expect this to work right out of the box. From what I understand UIImageViews have user interaction disabled by default, so I have enabled it, both via InterfaceBuilder and in my UIViewcontroller's viewDidLoad method (I have tied the UIImageView to an IBOutlet). I also am ensuring that userInteraction is enabled in the parent view in Interface Builder.
Anything else that I am forgetting here?
OK, I'm a dummy. It works fine. The problem was, I didn't realize I was sending a release message to the UIViewController without having retained it elsewhere first. So that was causing the problem.
It is hard to say what your problem is, I don't know what you mean by overriding it?
Make sure you are connecting the touchesBegan event with an IBAction in Interface Builder?
You must create a IBAction function to handle the event, and explicitly connect the even to the IBAction. It is not as simple as simply overriding a method.
Although you have the View tied to an IBOutlet, you need to connect the event using an IBAction, or else you won't get any of those events.
Please ignore the first answer. It is, in fact, as easy as overriding the method in the custom view. The most common reason for not receiving touchesBegan is the canBecomeFirstResponder method not being implemented. This is not an IB hookup, these are the standard methods for touch handling.
Related
I'm fairly new to Cocoa Touch. Right now I'm trying to subclass UIViewController to provide my custom view. Since I intend to save the content of a UITextField (passcodeField) using NSUserDefaults, I want to be notified whenever the UITextField changes its value.
I've read somewhere that in order to do that I should add the view controller to be an observer of the UITextFieldTextDidChangeNotification notification. However I'm just not sure when to do that. I've considered several options.
In the -loadView method. However, since I'm loading my view using a XIB, I think i shouldn't mess with this method and should instead leave it as-is. (Am I correct on this point, BTW? )
In the -viewWillAppear method. But this method may be called multiple times because the view may be moved out and into the screen without being destroyed and recreated. (Am I correct? ) This will not do any harm to the program but sure doesn't seem like the correct way.
In the initializer of the UIViewController. If I want to add the notification there I must reference the UITextField. By doing this I essentially cause the view to created before it is really needed. Also I think I read somewhere that if the system runs low on memory the offscreen views may be destroyed. Thus I may lose the notification observing if such thing happens, right?
So I'm totally confused right now. Could you guys give me some advice of where to put it? Thanks so much!
Put it in the - (void)viewDidLoad method of your ViewController remember to call [super viewDidLoad]; at the start of your implementation.
Is this possible in iOS, or do I really have to register a shake event detection in every single view controller?
I want that a user of my app can shake his iPhone to return to the root. Regardless of the current view controller.
I've done this by writing a category on UIViewController. This way you don't need to subclass anything, you can implement it even if the user interface has been finished already.
In my implementation, the VCs will respond to the shake unless the specific VC has opted out of the mechanism. Opting out is done by setting a BOOL ivar to NO in the specific implementation. The shake mechanism will look for this ivar using key-value-coding and ignore the shake if the ivar has been set.
I'd further refine this by allowing only the VC to respond which is currently visible.
edited post (old information was wrong)
in your case I would write my own ViewController which subclasses UIViewController, implements the motion-delegates of UIResponder and will then call the popToRootViewController on the navigationController-property of the ViewController. And everytimes you create a new ViewController you should subclass your ViewCOntroller and not UIViewController. So every ViewController is able to receive the shake-event but it is only written once in your code :)
This is just a guess, but maybe you could do it by subclassing UIApplication (not your app delegate, the actual application). UIApplication is a UIResponder, so you can make it the first responder, and provide a motionBegan or motionEnded method on it.
I'll try to explain as best I can:
I have two classes I'm currently focusing on. A Database Class and a View Controller, everything is currently set up like this:
View.h - Has "Database* myDatabase;"
View.m - Calls "OpenDB" during ViewLoad and has a button method that uses: [myDatabase getRow]; when clicked.
Database.h - Has "sqlite3 db;"
Database.m - Has "getRow" method and "openDB", which uses the "db" declared in Database.h.
This causes no errors during build, but when my program runs, when I click my button [myDatabase getRow]; does nothing. I used NSLog just inside the method and it never gets called. If it's hard to understand, I'll post code snippets, but I thought it would just be too much code.
Typically when you're not seeing a message that you're expecting to see, and the circumstances of it are completely baffling, it's because the receiver of the message is nil.
Put a breakpoint inside your viewDidLoad and make sure that myDatabase actually has a value assigned to it.
"po myDatabase" in gdb...
If in fact myDatabase is actually non-nil, then the second source of lots of grief trying to figure out why something's not happening the way you expect it to is missing connections in your XIB.
Make sure that your button's action is wired to your controller, or if you're programmatically setting the button's action, then make sure that your controller's outlet to the button is wired up.
You should create a object of Database class and access the methods using those objects.
Another workaround is to change those methods to static methods.
I have a custom UIViewController, which is the only subView of UIView. The UIViewController contains delegate function:
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
return YES;
}
This function is called once when the application starts and is never called again when the device is rotated. I also notice that the willRotateToInterfaceOrientation function is never called. I pretty much commented out all the content in the UIViewController but it is still not responding to device rotation.
I ended up solving my own problem by starting from stretch to create a brand new UIViewController and made sure it was responsive to the device rotation. I then brought in my code piece by piece and checked the rotation. In the end, I found the root cause. In my custom UIViewController, I had
- (id)initWithFrame:(CGRect)theframe {
if (self.view = [super.view initWithFrame:theframe])
It worked find excpet it did not respond to device roation even though I did not call the init function. The solution is simple. Add [self init] in the initWithFrame function. Thank you all for responding.
Your code looks correct. I suspect it's something in your .xib file (like the wrong object type for "File's Owner"), so that perhaps your view controller subclass isn't being instantiated at all. Put some logging into viewDidLoad and make sure it's getting called.
Try doing a test app that just tests the rotation problem. This will help isolate your issue.
You may need to implement that method in the controller of the parent UIView, as it seems your view is enclosed in another view.
I have a UIViewController that is initialised with a correct frame, however somewhere in my code the frame gets mangled and I'm having difficulty finding out where.
In situations like this it is usually handy to watch a variable in the debugger, however I have no way of accessing the controller->view->frame property in my variable view, since it isn't a variable, it's a property (surprisingly enough)
Drilling into the UIView in the variables display shows a few things but nothing I can relate to the frame, I thought perhaps that would be in layer but it isn't.
Is there any way to watch for changes in a private API? I guess not, since the variables are essentially 'hidden' and so you can't specify exactly what to watch.
Alternatively, what other approach could I use? I already tried subclassing UIView, setting my UIViewController's view to point to this subclass and breaking on the setFrame method but it didn't seem to work.
EDIT: the subclassing UIView method DID work, I just had to set the view to point to my test subclass in viewDidLoad and not the init method. Leaving this question open as I'm not sure if this is the best way of approaching this kind of problem...
Subclass your the view you want to track and rewrite the setFrame method:
#implementation MyTableView
- (void)setFrame:(CGRect)frame;
{
NSLog(#"%#", frame);
[super setFrame:frame];
}
#end
Then use the debugger to add a breakpoint to it and check when it gets called. Eventually, you'll see when the frame gets changed and where does the change comes from.
I discovered this can be done using key value observers.
http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/KeyValueObserving/KeyValueObserving.html
You could create an ivar, view2, and just assigned it to your view in your loadView method. That should enable you to watch it like a normal variable.