when my program starts for the first time, drawRect is automatically called and it prints the view.
When I call setNeedsDisplay, it does not call drawRect.
I have the IBOutlet correctly linked to the view and associated the view to the correct class.
thanks
Mohammed
Related
A normal answer would be, when the view will appear.
Say I have a UIViewController. Let's call that vc.
Say I want vc to control a view.
so I do vc.view = controlledView;
I expect everytime controlledView is about to appear then [vc viewWillAppear] will be called.
It doesn't.
What's wrong?
Also viewDidLoad is also not called even after I do
[vc view]
Technically, vc.view is already loaded
if you are calling viewWillAppear in any other file , with other View instance then it will never call.
viewWillAppear method calls every time when go to that view and if you leave it and then again come or come-back , it will call again.
please must use 'Super' keyword as.
[super viewWillAppear] in WillAppear method.
According to docs
This method is called before the receiver’s view is about to be added
to a view hierarchy and before any animations are configured for
showing the view. You can override this method to perform custom tasks
associated with displaying the view.
viewWillAppear is always called when your view is about to appear, as name itself suggests.
If a view controller is presented by a view controller inside of a popover, this method is not invoked on the presenting view controller after the presented controller is dismissed.
Life Cycle of view controller goes like this:
When a viewcontroller is allocated and loaded, loadView is called then viewDidLoad is called. You can see the entire flow as in image.
Refer to this image
NOTE: This image is taken from this answer
The right answer is the following.
Did you add the child viewController as the child of the parent child view controller.
viewWillAppear will only be called for the parent view controller (the top screen view controller) unless the other viewController is declared as the child.
Then the parentViewController will pass on viewWillAppear events.
I have a custom view controller with several subviews. Each of those subviews is connected to the view controller's .m file via IBOutlet properties. Those subviews have custom setters that adjust size of the other subviews depending on whether that subview is or is not displaying content.
Now it seems that these custom setters are being called by initWithCoder: prior to viewDidLoad being called. (I hope/assume this is normal.)
My issue is that calling self.view accesses the setter methods for self.view's subviews. My current understanding is that this should not be necessary. Can someone explain what's going on here? I'd rather this not happen as I'm not intending to set anything by accessing self.view.
Here is the code: https://github.com/kenmhaggerty/Sandbox
Calling self.view on a view controller causes it to load its view from the nib, if it hasn't already done so. This instantiates all objects in the nib (using initWithCoder:) and sets the values of any outlets (using your accessor methods). It then calls viewDidLoad, by which point everything in the nib will exist.
Your outlet setter methods are probably not an appropriate place to be making layout adjustments. Either use a constraint-based layout which will automatically adapt to changes in size of the subviews, or use viewDidLayoutSubviews, or use the methods you are using to pass model information to those subviews.
I understand that viewWillAppear will be called when duh.... when the the view is about to appear.
But how does IOS know that a controller's view is about to appear?
When exactly that and how it is implemented?
For example, does the childController.view check first that window is one of it's super ancestors? Does the view has a pointer to it's controller? How exactly that works? Does everytime a view is added it check whether it's window is it's super ancestor and whether it is the view outlet of a UIViewController?
For example, if I add childcontroller.view but not to a subview of any view that's being called. Will viewWillAppear called?
Does the childController need to be the a child of a parentController so that viewWillAppear of the childController will be called when the parentController's viewWillAppear is called automatically?
The view is loaded by your controller using the - (void)loadView method. This method is implemented to load a blank view or a view from a nib/storyboard. You only need to override it if you really need to create a view hierarchy from scratch.
All of the magic happens when the value of the view property is first requested and the controller detects the value is nil. All of the life cycle method calls are handled by the UIViewController. There is nothing you need to do other than implement the methods if you need them. Remember one thing: There is no guarantee the view has been loaded until the - (void)viewDidLoad method has been called.
Everything I've learned about controllers how they work has come from the View Controller Programming Guide.
Imagine I have a view controller called blueView and another called greenView. I then add greenView.view as a subview of blueView.view. Now suppose that after some user interaction, I'd like to remove greenView.view from blueView.view using:
[self.view removeFromSuperview]
What is actually happening here? Is blueView.view ever redrawn? I thought the viewDidLoad method might be called, however after putting an NSLog messge in viewDidLoad, it was never called after removing the subview. Any clarification as to what is actually happening when you remove a subview from its superview would be much appreciated.
First, a view controller is meant to manage an entire view hierarchy at once; you shouldn't have two view controllers (other than container controllers like UINavigationController) active at the same time. See this SO question and my answer to get a better understanding on this important point. So, the particular situation you describe shouldn't come up. (Aside: people often confuse views and view controllers, so it's not helpful to give your view controllers names ending in "-view", like "blueView." Call it "blueViewController" to help avoid confusion.)
Second, as #InsertWittyName points out, -viewDidLoad is a UIViewController method, not a UIView method. Taking that a step further, neither view controllers nor -viewDidLoad has any role in adding or removing subviews from a view. -viewDidLoad is called when the view controller's view is first created. It's basically just a way of deferring the view-related part of view controller initialization until after the view hierarchy has been created, so there's no reason that it'd be called again just because a subview was removed from the hierarchy.
Finally, exactly how a view removes itself from its superview is really an implementation detail -- it might call a private UIView method on the superview, or it might modify the superview's list of subviews directly, or something else. I don't see anything in the documentation that explicitly says that the superview will redraw itself after a subview has been removed, but in my experience the superview does indeed redraw itself. You can check this by putting a breakpoint on the -drawRect method of the superview.
Does the addSubview method actually load the view into the application or not? The reason I am asking is because I have two two views in my application. The application delegate adds the two views as subviews and then brings one of the views up front. Now, I have a print statement in each of the viewDidLoad methods for each view. When I run the application, the application delegate loads the views as subViews and as each view is loaded, I actually see the console print out the statements that I placed in each of the viewDidLoad methods. Is this supposed to be doing this?
viewDidLoad is actually a method of UIViewController, not UIView. It gets called after the view gets loaded into memory (after your init method, but before the awakeFromNib). You'll notice that addSubview: takes a UIView as a parameter, so the view must have been loaded in order for the view to be added to another view. Otherwise you'd be trying to add an imaginary view.
In answer to your question, yes it is supposed to be doing this. viewDidLoad is called long before you addSubview. In fact, if you take out the addSubview: lines, you'll notice that it's still getting called (because you're creating the view's controller).
My understanding is that views are lazily loaded. If your viewcontroller has 10 view, they are not all loaded until you actually try to access them.