I have a question regarding the custom init methods specifically on UIViewControllers. Let's say that I write an init method which takes one parameter (let's say UIViewControllerInitMode) and that parameter is responsible to indicate in which way the view should load. So when the viewDidLoad gets called that parameter (now stored as a class variable) gets checked and the GUI related content is loaded accordingly. How is this done?
Let's take this example:
We have a NS_ENUM called UIViewControllerInitMode with modes kUIViewControllerInitModeOne and kUIViewControllerInitModeTwo. Now for the init and viewDidLoad code:
- (instancetype)initWithMode:(UIViewControllerInitMode)m
{
self = [super init];
if (self)
{
mode = m; //Assume that mode is a class variable
}
return self;
}
- (void)viewDidLoad
{
[super viewDidLoad];
if (mode == kUIViewControllerInitModeOne) //Check the class variable
self.view.backgroundColor = [UIColor blueColor];
else //It's the InitModeTwo
self.view.backgroundColor = [UIColor redColor];
}
Now this looks like a perfectly legitimate piece of code (at least to me) but if my knowledge is correct the actual view of a UIViewController gets lazy loaded so there is no telling if the view is blue or red when the class variable gets set (except with an extra if but that looks ugly because it would mean I have the same code for GUI in init and in viewDidLoad). So does this mean that under some circumstances the view can have a red background even if I inited the controller with the mode that should make a blue background? Setting the background color in init is not safe for the same reason or is it? It always works if I do it in the way of the example above but I want to get to the bottom of this. How does this happen under the hood? Where am I right and/or wrong?
I see no problem with the code above. You are right that you should not touch UI components in the init as they are most likely null at that time. The initWithMode method should not care what color the view is as it is probably no color at all. The viewDidLoad method is for changing the display properties of the view and other UI components. Due to the fact that the init will always be called before the viewDidLoad, your view should always be set to either red or blue based on mode.
You example is perfectly fine. You can set the views properties after it is created. When you changes don't show up, you can ask the view to draw itself again by calling
[self.view setNeedsDisplay];
Setting the background color in init would fail, I guess, because the view isn't initialized in init yet. But I'm not sure about this. Just try it.
Related
I'm creating an overlay which will cover all displaying views on screen. This overlay always appears even in case rootViewController changes, pushing or presenting.
My idea is
Create CustomWindow which is a subclass of UIWindow. After that replacing default window of UIApplication with CustomWindow, create a new rootViewController for my new window.
In CustomWindow, I have an overlay (is an UIView). Overlay have light gray color with an alpha and every event on overlay will be pass through to below view.
Whenever CustomWindow add a new subview, i will bring overlay to front. It's make sure overlay will be on the top in every case.
CustomWindow
#implementation CustomWindow
- (instancetype)initWithFrame:(CGRect)frame {
self = [super initWithFrame:frame];
if (self) {
_overlay = [[UIView alloc] initWithFrame:self.bounds];
_overlay.userInteractionEnabled = NO;
_overlay.backgroundColor = [UIColor lightGrayColor];
_overlay.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
[self addSubview:_overlay];
}
return self;
}
- (void)didAddSubview:(UIView *)subview {
[super didAddSubview:subview];
[self bringSubviewToFront:_overlay];
}
#end
Everything works fine in every case even when pushing, presenting or changing rootViewController.
Problem
But when i show an UIActivityViewController, I can't click on any extensions which are displayed on UIActivityViewController.
Magically
When i click outside of UIActivityViewController or click on Cancel Button, UIActivityViewController is dismissed normally.
If i change color of overlay to clearColor, it works fine too.
My question is
How can i touch on extensions when i have overlay on window and overlay have a color ?
If i can't, can anyone tell me why it happens ? It's perfect when you can quote the reason from a document.
I'm pretty sure this doesn't relate to how i initialize UIActivityViewController or the way i show UIActivityViewController.
MORE
I found a problem quite similar to this problem on Android. But i'm not sure because i haven't seen any official document about it from Apple. One more thing is when changing color to clearColor can affect touch. So actually, i don't think they are same.
This is due to a UIRemoveView (private) in the hierarchy. As best I can determine, your app cannot forward events directly to remote views. I suspect this is a security measure to prevent you from presenting the share dialog and automatically sending a touch event to it to do an external action the user didn't request. Remote views don't run in your application's process. The "Copy" button is interacted with across an XPC link.
This all means that if the remote view is covered by one of your views, there's no way (at least that I've found) to interact with it. You have to ensure that you're not covering it.
Actually doing that is simple. The thing that holds the remote view is called a UITransitionView and is used for other OS-level things that you probably shouldn't be covering either. So don't:
- (void)didAddSubview:(UIView *)subview {
[super didAddSubview:subview];
if ([subview isKindOfClass:NSClassFromString(#"UITransitionView")]) {
// To raise it above your overlay;
// otherwise it's immediately above the view controller (below the overlay)
[self bringSubviewToFront:subview];
} else {
[self bringSubviewToFront:self.overlay];
}
}
But.... This requires you to talk about UITransitionView in your code. This is both fragile, and possibly a forbidden use of private APIs.
Otherwise you'll have to wrap your UIActivityViewController requests with some call/notification that tells the window not to cover views until we're done (which you'll have to clear in the completion handler).
I want to override the loadView method of my custom view controller in order to customise the view that is being shown. For that custom view I want to apply the background color that was set in the Storyboard editor.
If I for example implement loadView like this:
-(void)loadView{
self.view = [[MyCustomView alloc] init];
//Do some initialisation work for the custom view
//...
}
Then the resulting view has a black background. However, if I only call the default implementation:
-(void)loadView{
[super loadView];
}
Then the orange background color (see screenshot) is applied to the view. How can I get the color that was set in Storyboard editor? I would like to do something like this (pseudo code):
-(void)loadView{
self.view = [[MyCustomView alloc] init];
self.view.backgroundColor = [self colorThatWasSelectedInStoryboardEditor];
//Do some initialisation work for the custom view
//...
}
How does apple achieve that in the default implementation of loadView?
Since you apparently really want to use "loadView" here instead of "viewDidLoad", AND Apple's documentation for loadView says NOT to call "super", you will need to "hide" your custom color somewhere else. E.G. some other view (e.g. a hidden one?) in your ViewController, where it's connected to an IBOutlet and where you can extract it via the view's ".backgroundColor" property.
Or you will need to set your ".backgroundColor" property via good ol' UIColor methods like "colorWithRed:green:blue:alpha:".
All your views from the Storyboard are laid out before viewWillAppear:, which means, in viewDidLoad you don't have them yet. Try moving your code to viewWillAppear:, or even better, to viewWill/DidLayoutSubviews and than self.view.backgroundColor will give you the one you set in the IB.
To answer the question in your comment, go to the IB, select your view, go to the Identity Inspector tab under the Utilities (right) pane, and set a custom class to be MyCustomView. No need to implement loadView to do that.
e.g. a UIView that I have declared as a custom view class AGBlurView:
I had this question when/where to create and initialize views that are created programatically, so I hope some discussions here will shed more light on this topic for me.
This slide:
says: "not to initialize something based on the geometry of the view in viewDidLoad" and suggests viewDidAppear.
Imagine my view controller has view. I want to add 10 dynamic UIButtons to it.
Shall I put the code like below to the viewDidAppear?
-(void) viewDidAppear:(BOOL)animated
{
...
UIButton *button1 = [[UIButton alloc] initWithFrame: rect1];
[self.view addSubview: button1];
UIButton *button2 = [[UIButton alloc] initWithFrame: rect2];
[self.view addSubview: button2];
...
}
But this creates the buttons each time the view is shown. Is it what we want?
On the other hand if I put the code in viewDidLoad slide suggest not to initialize geometry of these views there.
Or shall we create buttons in viewDidLoad and set their frames in viewDidAppear?
What approach do you usually take?
But this creates the buttons each time the view is shown. It's true.
So the best thing you can do is to add a boolean (lets name it isLaunched). You set it to FALSE in the method -(void)viewDidLoad
Then add a if condition in your -(void)viewDidAppear where you perform creation of buttons (or other stuff) and set the boolean to true at the end.
You should have something like that :
-(void)viewDidLoad
{
//some settings
isLaunched = FALSE;
}
-(void)viewDidAppear:(BOOL)animated
{
if(!isLaunched)
{
//creating and adding buttons
isLaunched = TRUE;
}
}
zbMax (and now Amar) offered good solutions to implement the view creations in viewDidAppear: I will provide the rational for doing this (over viewDidLoad).
It is pretty simple actually. In viewDidLoad none of the views are actually setup yet, so any attempt to set/create frames or bounds will be extremely inconsistent. Struts and springs (or autolayout) will take effect after this method which will create additional changes to your views. viewDidAppear: is the correct place to do this because you can now rely on existing views and setting frames.
Reason for not playing with the geometry in viewDidLoad is because view is still in the memory and not on the window. Once the view is put on the window, then you can specify geometry. That happens when viewDidAppear is called for your controller.
As recommended, you should do all the initialisation in viewDidLoad as this is one time task and need not be repeated. Hold references to the added subviews and give them appropriate frame in viewDidAppear.
When you are dealing with custom UIView and its subviews, layoutSubviews is the method you need to override in the custom view in order to rearrange the geometry of its subviews.
Hope that helps!
Everybody knows that you can't trust the frame size on a UIViewController init/viewDidLoad method; this:
- (void)viewDidLoad: {
NSLog(#"%d", self.view.frame.size.width);
}
will print wrong sizes in many occasions (in particular it's pretty much broken in landscape mode)
This will actually return always corrected results so it's good to layout the subviews:
- (void)viewWillAppear: {
NSLog(#"%d", self.view.frame.size.width);
}
The problem is that viewWillAppears gets called every time the view appears, so it's not suitable to alloc or add subviews. So you end up declaring every single view in the interface and you end up with huge header files that I don't like at all since most of the items don't need any more manipulations after the initial setup.
So question one is: Is there a better way to handle subviews positioning?
Question two is very related, let's say I have a subclass of UIView including various others subviews. I declare it inside my interface, and i alloc/init it in my init/viewDidLoad method.
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
...
menu = [[SNKSlidingMenu alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height);
...
}
As we already know we now need to reposition it in viewWillAppear to get a more accurate reading
- (void)viewWillAppear:(BOOL)animated{
....
menu.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height);
....
}
The problem is that of course all the subviews needs to be repositioned as well. This is done by the layoutSubviews function that get called automatically, but we got the same problem: All the subviews need to be declared inside the interface of the SNKSlidingMenu class.. Is there a way around this?
Thanks.
If you are targetting iOS 5.0 or better you can use viewWillLayoutSubviews and viewDidLayoutSubviews to make changes.
As for your second question, if you need access to an instance variable in other method than init, you need to keep it around, I don't see a problem with it.
You can, however, try to use Auto Layouts and set up rules between the subviews so it's automatically laid out for you without the need to keep a reference.
viewDidLoad only gets called when your view is created, but lots of things can affect the frame's size, and it doesn't get called again when frame changes.
Instead:
create subviews in viewDidLoad
set their sizes in
viewWillLayoutSubviews.
See some additional discussion here for handling rotation: https://stackoverflow.com/a/16421170/1445366
viewWillLayoutSubviews and viewDidLayoutSubviews can resolve this problem.
But the two methed would be performed more times.
this is my code to get correct self.view.frame.
- (void)viewDidLoad {
[super viewDidLoad];
...
dispatch_async(dispatch_get_main_queue(), ^{
// init you view and set it`s frame. this can get correct frame.
...
}
...
}
This saved my life more than once (Swift 4):
override func viewDidLoad() {
super.viewDidLoad()
self.view.setNeedsLayout()
self.view.layoutIfNeeded()
}
Basically this forces the viewcontroller to correctly layout it's view and from there you can get the correct frames for all your subviews. This particularly helps when doing transition animations and your view controllers are using autolayout and interface builder.
From what I've noticed it looks like the initial frames are set to whatever your interface builder's default size class is set to. I normally edit using the iPhone XS size class so in viewDidLoad it seems that the view's width is always 375 regardless whether you are using an iPhone XR or not. This corrects itself before viewWillAppear though.
The above code will correct this issue and allow you to get the correct frames for your view / subviews before the view controller is rendered to the screen.
I have a TestView inherited from UIView, and everything is drawn on the screen using its drawRect method.
But if I don't want drawRect to clear the view before drawing, I used
self.clearsContextBeforeDrawing = NO;
self.opaque = NO; // also added because the doc says the rect
// passed to drawRect will be filled with
// background color first if it is set to YES
in the initWithFrame method.
The drawRect method is invoked by using
[self.view setNeedsDisplay];
in the ViewController event handler. (for touchesMoved events)
But still, everything is cleared before anything is drawn? How to make it work?
I think this answers your question. From the answer:
You cannot prevent the contents from being erased by doing the following:
[self setClearsContextBeforeDrawing: NO];
This is merely a hint to the graphics engine that there is no point in having it pre-clear the view for you, since you will likely need to re-draw the whole area anyway. It may prevent your view from being automatically erased, but you cannot depend on it.