While I was working with ios apps suddenly one question struct in my mind. What if I want to reload whole view? What will happen if I invoke viewDidLoad? Is that the right way to do this? I'm asking just for my knowledge only.
If the view is the main view of some controller, you can reload it by setting the controller’s view property to nil – it will be loaded again the next time somebody uses the view property. Invoking -viewDidLoad would not work, it’s just a callback method called by some UIViewController code when the view is finished loading.
You may use following simple code to reload view.
[YOUR_VIEW setNeedsDisplay];
If you want to reload the whole view, you can use reloadInputViews method or write the code in viewWillAppear , so everytime you make a new object of your viewController, the code in viewWillAppear will recall itself.
Related
I am working on an IPhone app that, through viewDidLoad, makes a connection and pulls data into a table. I would like the controller, or at least the table, to reload every time the controller is displayed, even if someone just switched from one tab to another or closed and re-opened the app on this controller. Is there a way to do this? I can't seem to find anything, it's also kind of a hard thing to search for. I have found discussions of when to put code in viewDidLoad but not another method that is run every them the controller displays.
Thanks,
Cheryl
You want to use
-(void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
//code to reload table viewdata
}
Each time the view appears this method is called. I use this a lot in my app.
There's no way to do it by injecting code in only one place.
You can think of a workaround, like for example sending custom "reload request" notification from required parts of code:
viewDidAppear: in your view controller
applicationDidBecomeActive: (if table is presented)
tabBarController:didSelectViewController: (if switched onto controller with the table)
tabBar:didSelectItem: (same as above)
etc.
In you view controller simply observe this notification and reload data when required.
Although, whats more important: do you really need to reload data under such harsh requirements? In most cases data reload happens when
view controller's viewDidLoad: is called
it is manually initiated (button, for example)
long time passed since the last update was received
Otherwise it's just an overkill.
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.
I have UITableViewController where I need to put initialization code only once to populate data source. in which method to put this code.
I tried with viewWillAppear: method, but it get executed every time view appear.
if you want to display things only once that the View has comed on screen, then yeah. go for it. Otherwise you also have ViewdidLoad or ViewWillAppear if you have to arrange things before the view begins the transition to slide in.
All of these methods will be executed every time from the tableView you tap on a row.
anyway the pattern you are trying to achieve is called singleton, you can find out about it more over here
What should my Objective-C singleton look like?
You can put it in viewDidLoad and it will be only once.
The - (void)viewDidLoad method is probably the place you want use. It gets called once the view controller has finished doing its loading code (either by loading a XIB or by calling loadView).
I have a bunch of pages I am chaining together and presenting as modal view controllers. THey all have viewDidLoad methods. It seems that when one is loaded though it calls the viewDidLoad methods of ones in the background too. How can I stop this? Thanks!
You can't. The viewDidLoad method will get called when the view is loaded. Asking a view controller for its view loads the view.
Consider moving code into your viewWillAppear:(BOOL)animated method. That way it will only get called before the view is actually shown to the user.
I have a UITabBar with a number of UITabBarItems. I've assigned a different view controller to each of these.
I want to load some data etc., when each button is clicked. Therefore I will like to know where to put that code? I tried implementing viewWillAppear and viewDidLoad in the view controller but those didn't get called.
I know that when you assign a delegate to a UINavigationController, the component UIViewController delegate methods are not called. It seems likely that the same is true of UITabBarController.
I would try implementing the UITabBarControllerDelegate protocol and implementing the tabBar:didSelectViewController: method.
Are you sure your custom controllers inherit from UIViewController?
Don't forget the signature for the viewWillAppear is viewWillAppear:animated:
I'm working off the beta 5 right now, and it works just fine (I'm also using a TabBar).
Write your code in viewdidappear function.but i didn't try