Custom UITabBar subclass without Interface Builder - ios

Using IB (be it with a Storyboard or a XIB), one can easily have the UITabBarController use a subclass of UITabBar, by editing the class name in the Identity Inspector -> Custom Class.
How to mimic this "custom class" feature of IB, without using it at all ?
I tried the following (in my subclass of UITabBarController) :
var customTabBar = MyCustomTabBarSubclass()
override var tabBar: UITabBar {
return customTabBar
}
To no avail – the tab bar is displayed, but blank. The issue is not elsewhere since returning super.tabBar from the overriden var fixes it.
The issue, I guess, is that I'm not setting up my customTabBar (frame, position, adding it to the view hierarchy), but I'd like to have the UITabBarController loadView (I think that's the one, not sure) do it for me, the same way it sets up any other UITabBar.
Ideas ?

I think you can't. For this question, I had some time to scan through the documentations of UITabBar and UITabBarController.
The tabBar property of UITabBarController is a get-only.
#available(iOS 3.0, *)
open var tabBar: UITabBar { get } // Provided for -[UIActionSheet showFromTabBar:]. Attempting to modify the contents of the tab bar directly will throw an exception.
Furthermore, it is stated in UITabBarController's documentation that you shouldn't manipulate such property.
You should never attempt to manipulate the UITabBar object itself
stored in this property. If you attempt to do so, the tab bar view
throws an exception. To configure the items for your tab bar
interface, you should instead assign one or more custom view
controllers to the viewControllers property. The tab bar collects the
needed tab bar items from the view controllers you specify.
The tab bar view provided by this property is only for situations
where you want to display an action sheet using the show(from:) method
of the UIActionSheet class.
Just wanna add: but unlike this UITabBarController, subclassing the UINavigationController gives you the power to init such subclass with a subclass of UINavigationBar:
UINavigationController(navigationBarClass: <#T##AnyClass?#>, toolbarClass: <#T##AnyClass?#>)
Unfortunately, UITabBarController does not have such kind of init method.

This works, but there's a chance you might not pass App Store review because it's setting a value that public API doesn't allow you to set.
Inside your UITabBarController's subclass' initWithNibName:bundle: or viewDidLoad, add this:
MyCustomTabBar *customTabBar = [[MyCustomTabBar alloc] initWithFrame:CGRectZero];
customTabBar.delegate = self;
[self setValue:customTabBar forKey:#"tabBar"];
Consider this just a proof of concept, not something you should necessarily use in your production app because it's technically using a private setTabBar: method.

If you choose to disregard what Apple says about what's supported (using a custom UITabBar subclass with Interface Builder, and only with it), here's a dirty solution (that works) :
It requires mild knowledge of the ObjC runtime, because we're going to swizzle stuff around... Essentially, the issue is that I can't force UITabBarController to instantiate the class I want it to instantiate (here, MyCustomTabBarSubclass). Instead, it always instantiates UITabBar.
But I know how it instantiates it : by calling -[[UITabBar alloc] initWithFrame:]. And I also know that all functions belonging to the init family are allowed to return either an instance of their class, or of a subclass (that's the basis of Class Clusters).
So, I'm going to use this. I'm going to swizzle (= replace the implementation) of UITabBar's -initWithFrame: method with my custom version of it, that, instead of calling up (self = [super initWithFrame:]) will call "down" (self = [MyCustomTabBarSubclass.alloc initWithFrame:]). Thus, the returned object will be of class MyCustomTabBarSubclass, which is what I'm trying to achieve.
Note how I'm calling MyCustomTabBarSubclass.alloc – this is because my subclass potentially has ivars that UITabBar does not have, thus making it larger in its memory layout. I might have to release self before reallocating it, otherwise I could be leaking the allocated memory, but I'm not sure at all (and ARC "forbids" me to do call -release, so I'd have to use another step of trickery to call it).
EDIT
(First thing, this method would also work for any case where IB's custom classes are of use).
Also note that implementing this requires writing ObjC code, as Swift does not allow us to call alloc, for instance – no pun intended. Here's the code :
IMP originalImp = NULL;
id __Swizzle_InitWithFrame(id self, SEL _cmd, CGRect frame)
{
Class c = NSClassFromString(#"MyBundleName.MyCustomTabBarSubclass");
self = [c alloc]; //so that we'll return an instance of MyCustomTabBarSubclass
if (self) {
id (*castedImp)(id, SEL, CGRect) = (id (*)(id, SEL, CGRect))originalImp;
self = castedImp(self, _cmd, frame); //-[super initWithFrame:]
}
return self;
}
You'll also have to ensure that the actual swizzling operation is only performed once (such as, dispatch_once). Here's the code that actually swizzles :
Method method = class_getInstanceMethod(NSClassFromString(#"UITabBar"), #selector(initWithFrame:));
IMP swizzleImp = (IMP)__Swizzle_InitWithFrame;
originalImp = method_setImplementation(method, swizzleImp);
So that's it for the ObjC side.
Swift-side :
#objc class MyCustomTabBarSubclass: UITabBar {
lazy var anIvar: Int = 0 //just a example obviously
// don't forget to make all your ivars lazy or optional
// because the initialisers WILL NOT BE CALLED, as we are
// circumventing the Swift runtime normal init mechanism
}
And before you initialise your UITabBarController, don't forget to call the ObjC code that performs the swizzling.
That's it ! You have cheated UITabBarController into instantiating your own subclass of UITabBar, and not the vanilla one. If you're working in pure ObjC, things are even easier (no messing with bridging headers, a subject I didn't cover here).
Obligatory DISCLAIMER : Messing with the ObjectiveC runtime is obviously not something to do lightly. Ensure you have no better solution – IMHO, using a XIB only for the purpose of avoiding such tinkering is a better idea than implementing my suggestion.
A example of issue that could arise : if you're using multiple tab bars in your app, you might not want all of them to be MyCustomTabBarSubclass instances. Using my code above without modifications would result in all tab bars to be instances of MyCustomTabBarSubclass, so you'd have to find a way to tell __Swizzle_InitWithFrame directly call the original implementation, or not.

Related

Can the same ViewController.view be added as subview to different views as a Singleton?

My app has a search view(search bar) which is used all over the app. I don't want to create duplicated code so I created a view controller called MySearchViewController to handle the search job, then I created a singleton object in AppDelegate. In every view controller, I added my search view like this:
- (void)viewDidLoad
{
MySearchViewController* search = [AppDelegate searchViewController];
[self.view addSubView:search.view];
}
My questions, Is it a good way? It's a singleton so it can be added to many views. Do I need to remove the view from last view before adding to current view?
Understand that you are mixing some concepts that are not necessarily related: avoid duplicated code and Singletons.
Wikipedia says this about singletons:
In software engineering, the singleton pattern is a design pattern that restricts the instantiation of a class to one object. This is useful when exactly one object is needed to coordinate actions across the system. The concept is sometimes generalized to systems that operate more efficiently when only one object exists, or that restrict the instantiation to a certain number of objects. The term comes from the mathematical concept of a singleton.
The most important characteristic of a singleton (in my humble opinion) is that the object is instantiated only once and every single place in your application will use the same instance. Well, to use your search feature everywhere and avoid duplicated code you don't need the search view to be instantiated only once, maybe the data that comes with it, but not the view itself.
Two better ways of achieving this:
1 - You can create a ViewController with your search and just embed this on the other views using a Container View, you can use blocks or a delegate protocol to communicate between your controller and the view that is embedding it.
2 - You can create a Parent class of the ViewController that will include the search bar, like a SearchViewController and all the other viewControllers that needs the same feature will inherit from it.
The singleton could be useful if you are planing to share the same search data and text between all the ViewControllers of the application, but it would be a singleton only with these information, the UISearchBar and all other view elements should not be part of the singleton.
Ideally, you should instantiate a fresh instance of MySearchViewController every time when you want to add it to another view to avoid problems.
Do I need to remove the view from last view before adding to current view?
Its not required to remove it from previous super view because whenever you add this singleton MySearchViewController's view to some other view, it will automatically gets removed from last super view and now its super view is your new view where you have added it.
If you want to add a view from a different view controller, your view controller has to be that view controller's parent view controller:
- (void)viewDidLoad
{
MySearchViewController* search = [AppDelegate searchViewController];
[self addChildViewController:search];
[self.view addSubView:search.view];
}
also, make sure that when the search.view is added, it is already initialised.
Why you do not use NSObject class ?, i do not know your requirement , but if you want to store latest updated value in whole project(in execution) then you should use the singleton, but if you do not want to store value (i mean one result for whole project) then you should use NSObject derived Class. advantage is singleton consumes memory so memory will be wasted. NSObject class will be reusable and only allocated when it is required and then ARC will take care of all things. If you want to know how to create NSObject and use of it then you can give me reply.
Here is some code to load a XIB as part of a custom object with the object gets initialized.
Why are you not creating custom search component for search?
you can use this component all over the app.
also this is not creating duplicat code.
- (id)initWithFrame:(CGRect)frame {
self = [super initWithFrame:frame];
if (self) {
// Initialization code
[[[NSBundle mainBundle] loadNibNamed:#"SearchView" owner:self options:nil] objectAtIndex:0];
[self addSubview:self.view];
self.frame = self.view.frame;
}
return self;
}
Please check below code. Hope this is work for you.
- (void)viewDidLoad
{
if ([self.view viewWithTag:123456]) {
[[self.view viewWithTag:123456] removeFromSuperview];
}
MySearchViewController* search = [AppDelegate searchViewController];
search.view.tag = 123456; // give a any random tag to view
[self.view addSubView:search.view];
[self addChildViewController:search];
}
Please make sure given tag is not assign to other object except search.view in self.view.
Thanks

Clean way to force view to load subviews early

Recently I wrote some code where I tried to refer to an outlet on a UIViewController I'd just instantiated with [storyboard instantiateViewControllerWithIdentifier] and modify the subview that the outlet pointed to before presenting the ViewController. It didn't work because the ViewController's view hadn't loaded its subviews yet, including the one that my outlet referred to, so the property just gave me a null pointer.
After (with some struggle) tracking down the cause of my issue in the debugger, I Googled around and learned, through answers like this one, that I can cause the view to load its subviews without being displayed by calling the myViewController.view getter. After that, I can access my outlet without any problems.
It's a clear hack, though, and Xcode - quite rightly - doesn't like it, and angrily protests with this warning:
Property access result unused - getters should not be used for side effects
Is there a non-hacky alternative way to do this that doesn't involved abusing the .view getter? Alternatively, are there canonical/idiomatic patterns for this scenario involving something like dynamically adding a handler to be called as soon as the subviews are loaded?
Or is the standard solution just to replace myViewController.view with [myViewController view] to shut up Xcode's warning, and then live with the hack?
On iOS 9 or newer, one can use:
viewController.loadViewIfNeeded()
Docs: https://developer.apple.com/reference/uikit/uiviewcontroller/1621446-loadviewifneeded
I agree that forcing a view to load should be avoided but I ran into a case where it seemed the only reasonable solution to a problem (popping a UINavigationController containing a UISearchController that had yet to be invoked causes a nasty console says warning).
What I did was use new iOS9 API loadViewIfNeeded and for pre-iOS9 used viewController.view.alpha = 1.0. Of course a good comment above this code will prevent you (or someone else) removing this code later thinking it is unneeded.
The fact that Apple is now providing this API signals it can be needed from time to time.
Not sure how much cleaner this way, but it still works fine:
_ = vc.view
UPD: for your convenience, you can declare extension like below:
extension UIViewController {
func preloadView() {
let _ = view
}
}
You can read explaination by following URL: https://www.natashatherobot.com/ios-testing-view-controllers-swift/
merged Rudolph/Swany answers for pre ios9 deployment targets
if #available(iOS 9.0, *) {
loadViewIfNeeded()
}
else {
// _ = self.view works but some Swift compiler genius could optimize what seems like a noop out
// hence this perversion from this recipe http://stackoverflow.com/questions/17279604/clean-way-to-force-view-to-load-subviews-early
view.alpha = 1
}
If I understand you correctly, I think there's another fairly standard solution: move the outlet modification/configuration code into a viewDidLoad method (of the recently instantiated VC).
The topic is also discussed in this question.
It would require some restructuring, but it might give you a "cleaner" design in terms of MVC if your incoming VC handled its own configuration, and it would avoid the "You should never call this method directly" stricture on loadView.
You can call [myViewController loadView] to explicitly load the view, instead of abusing the .view getter. The .view getter actually calls loadView if necessary when called.
It's still not a very nice solution, since the UIView Documentation's section on loadView explicitly instructs that
You should never call this method directly

Is it possible to access a property in the superclass from a subclass that belong to subclassed element?

I am sub-classing a UIScrollView element in response to a previous question suggestion.
In my subclass I have a few methods that are triggered by touch and keyboard events. Those events need to interact in various ways with variables that are in my superview.
I've tried accessing them via _myVar.text = #"smth" but that doesnt compile.
I know I could play back and forth with NSNotifications but is there a way to access the variables in my superview / class from my UISCrollView subclass?
I've tried self.myVar = #"" but it says that it is not recgonised. I am subclassing an UIScrollView element but then my view that hold all my variables is a UIViewController. just the UISCroll element was subclassed
Everything that is a #property in your superclass is accessible in your subclass, but not in the other way
It sounds like you're a little confused here. Are you sure you're talking about the superview? Or are you talking about the superclass from which you derived your subclass? If superview, and if you know the type of the superview, get a pointer to it, cast it to the appropriate class type, then call methods on it or access its visible properties.
UIButton* superButton = (UIButton*)[self superview];
superButton.visible = NO; // Assign to superview property
If you're talking about the superclass (in your case UIScrollView), then yes of course you can use any of its visible methods and properties.
self.bounces = YES; // Assign to superclass property
In case it's not clear what the difference is, you should really do some more reading about the basics of Objective-C and object oriented programming.
Superview: the view relative to which this view is laid out. This view is a subview of the superview. UIView and all derived classes have this hierarchical relationship.
Superclass: the class whose functionality you are extending to define your subclass. Your subclass inherits all visible properties and methods.
So much confusion, where to start? I really don't know. For what it's worth,
_myVar.text = "#"smth"
will obviously not compile, note the stray ".
_myVar.text = "#smth"
has a better chance of compiling.

MonoTouch custom UIButton crashes on load: Selector invoked from objective-c on a managed object that has been GC'd

I am using MonoTouch and have created a class MyButton that extends UIButton. This is actually a simplified example of the same problem I was having with a custom UIScrollView. MyButton extends UIButton and adds some methods to do something simple like increment and decrement a counter (this is just a test case). I also include '[Register("MyButton")]' before my class definition so that it registers with Interface Builder (IB) so that I can add a UIButton and specify its class as MyButton.
What works:
I can add an instance of MyButton programmatically to my main view and it displays properly and functions as expected.
What doesn't work:
If I try to add a UIButton from IB and specify its class as MyButton, then add an outlet and also specify it is a MyButton type then my app crashes while trying to load the main view with the exception: Unhandled managed exception: Selector invoked from objective-c on a managed object of type iOSCustomUIView.MyButton (0xC2F40D0) that has been GC'ed (System.Exception).
I have found similar questions that have this problem but with view controllers, not views. So I understand that the error is similar, but in the case of a view controller references are lost when pushing new controllers onto the stack, etc. In my case, I don't know why my object has been GC'd before anything has loaded.
I have tried creating additional private member variables to reference my MyButton outlet (btnIncrement), but this did not help. I set breakpoints and the crash occurs when trying to instantiate a new instance of my view controller: (from AppDelegate.cs)
public override bool FinishedLaunching (UIApplication app, NSDictionary options)
{
window = new UIWindow (UIScreen.MainScreen.Bounds);
viewController = new iOSCustomUIViewViewController ();
window.RootViewController = viewController;
window.MakeKeyAndVisible ();
return true;
}
Is there anything I am missing in order to define a custom UIButton class and use it in IB? Is this a bug in MonoTouch?
I got a great response from adamkemp on the Xamarin forum. The solution is that I need to write a constructor that accepts an IntPtr p argument since that is the constructor called when view objects are created from xib files. In my case, I simply define the following constructor:
public MyButton(IntPtr p) : base(p)
{
// Do initialization stuff here
}
Since I did not have this constructor defined, my object was likely never created. The log message saying that my object has been GC'd was a little misleading in this case. Now, my app views all load successfully.

ios I want to access an object in MainViewController from AppDelegate

I used this line from the sample project AppPrefs:
UITableView *tableView = ((UITableViewController *)self.navController.visibleViewController).tableView;
and it works of course perfectly,
so I tried:
UISearchBar *searchBar = (UIViewController *)mySearchBar;
but I get warning that mySearchBar is undeclared, even it is a property and initialized in MainViewController (which is of class UIViewController).
I need to access various objects in MainViewController from AppDelegate, so the app could refresh itself whenever the settings is changed.
Ouch, your code is wrong at as much places as possible. Let me explain where:
One. You're casting mySearchBar to UIViewController * then assign it to a different pointer type (of type UISearchBar *).
Two. If you're writing this from the app delegate, how come the compiler should know which class' (even further, which object's) property are you using? There may be multiple objects/classes with a property of the same name.
I feel you're confusing typecasting and accessing properties (so I strongly recommend learning plain C correctly before digging straight into iOS development as this is such a basic question that you will likely produce low-quality code if you don't yet understand this). You should maintain an instance of your view controller (either make it a global variable, a singleton, or even better, a property of the application delegate object) and acces it from there. Example:
UISearchBar *bar = [[[[UIApplication sharedApplication] delegate] mainViewController] searchBar];
If "mySearchBar" its a property declared in your MainViewController, and your self.navController.visibleController is an instance of MainViewController. Just access it like this:
UISearchBar* searchBar= self.navController.visibleController.mySearchBar
Now you are trying to assign something that doesn't even exist in your AppDelegate, because mySearchBar has not been declared in your AppDelegate.

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