I am quite new to iOS programming so please be nice :) I am trying to google out this for hours now with no success. I have setup an iOS master detail project.
What i need to do. is to change a label in the detailViewController when the app calls applicationDidEnterBackground
This is my faulty code in the appdelegate applicationDidEnterBackground method
UIViewController *temp = [self.navigationController visibleViewController];
NSLog(#"%#",[temp nibName]);
if ([temp nibName] == #"DetailViewController") {
temp._lblBrewingTime = #"";
}
This doesnt work. semantic issue: lblbrewingtime not found on object of type UIViewController.
If I add a breakpoint and check the structure of the temp pointer. I can see the _lblBrewingTime type.
Can you please point me how to get the properties of whatever view is currently loaded in the app delegate?
thank you very much,
Greets,
Nick
You have to explicitly cast it to DetailViewController, once you are sure that the visibleViewController is DetailViewController actually.
So here's the fix:-
UIViewController *temp = [self.navigationController visibleViewController];
NSLog(#"%#",[temp nibName]);
if ([temp nibName] == #"DetailViewController") {
DetailViewController* tempDVCObj = (DetailViewController*)temp;
//temp._lblBrewingTime = #"";
tempDVCObj._lblBrewingTime = #"";
}
And it says absolutely correct that your property _lblBrewingTime is not the property of UIViewController, it's the property of DetailViewController i.e. a subclass of UIViewController.
Some things here:
You should keep a reference to your main controller in the AppDelegate and access the view through this reference - the visible view controller in the navigation controller may not be your view controller class, e.g. because you navigated to another view.
You access the view controller via the UIViewController interface. The UIViewController class does not know about your child view controller's properties, so it cannot access the _lblBrewingType. You have to use your view controller's class name to access its properties, e.g. MyViewController * myVc = (MyViewController*)viewController.
_lblBrewingType looks like an internal variable of your view controller. To access it from the outside, you must provide it as a property:
// MyViewController.h
#interface MyViewController : UIViewController
{
UILabel* _lblBrewingType;
}
#property (strong, nonatomic) IBOutlet UILabel *lblBrewingType;
And the implementation:
// MyViewController.m
#implementation MyViewController
#synthesize lblBrewingType;
#end
Related
How can I access the value from an inputField located in a second viewController?
The class name of the second view controller is SettingsViewController and the outlet name for the inputField is setRateInput.
I tried this but it didn't work…
double taxRateFromInput = [[self.settings.setRateInput text]doubleValue];
when I NSLog it comes out as The value is: (null)
Any idea what I'm doing wrong?
Here is the implementation file for the main viewController:
#import "SettingsViewController.h"
#interface ViewController ()
#property (strong, nonatomic) SettingsViewController * settings;
#end
#implementation ViewController
// lazy instantiation
-( SettingsViewController *) settings
{
if (_settings == nil) {
_settings = [[SettingsViewController alloc]init];
}
return _settings;
}
- (IBAction)calculatePrice:(id)sender {
double taxRateFromInput = [[self.settings.setRateInput text]doubleValue];
#end
In theory, you could create a global. Create a new class, call it something like taxRate (.h and .m)
In taxRate.h, add the following code:
#import <Foundation/Foundation.h>
#class MyTaxRate;
#interface TaxRate : NSObject {
}
#property (nonatomic, retain) double * taxRateFromInput;
+(TaxRate*)getInstance;
#end
Then, in your controller, put a "#import taxRate.h" in there. In your .m file, add the following:
#import "TaxRate.h"
#implementation TaxRate
#synthesize taxRateFromInput;
static TaxRate *instance =nil;
+(TaxRate *)getInstance
{
#synchronized(self)
{
if(instance==nil)
{
instance= [TaxRate new];
}
}
return instance;
}
#end
Note: This is extremely similar in structure to what I'm purposing.
if you have the reference from the object view controller you can just access by the property from your attribute.
You instantiated a new SettingsViewController, but you didn't do anything to instantiate its textfield setRateInput. You can do it when you instantiate it:
_settings = [[SettingsViewController alloc]init];
_settings.setRateInput = [UITextField alloc] initWithFrame:someFrame]];
or, as a beter solution, instantiate the text field in -init of SettingsViewController
- init {
if (self = [super init] {
self.setRateInput = [UITextField alloc] initWithFrame:someFrame]];
}
return self;
}
If you use nib files, this would be a lot easier.
Note: setRateInput is a bad name for a property. Consider rateTextField instead.
Edit I forgot to add that you have to add the text field as a subview to its parent view.
So it will be like,
_settings = [[SettingsViewController alloc]init];
_settings.setRateInput = [[UITextField alloc] initWithFrame:someFrame] autorelease];
[_settings.view addSubView:_settings.setRateInput];
In this case, the setRateInput is retained by its super view. You're not using ARC, so you can call autorelease on your text field.
The better solution: Use - (void) loadView; inside SettingsViewController. Loading the view is the responsibility of the correspondent view controller.
- (void) loadView {
self.setRateInput = [[UITextField alloc] initWithFrame:someFrame] autorelease];
[self.view addSubView:_settings.setRateInput];
}
Edit: xib files and storyboards can help you out. Give these tutorials a try.
You are on the right track, also well done with your lazy instantiation (as
a demonstration that you grasped the concept, I mean).
But note, that outlets don't get connected until viewDidLoad is called. So if you
just alloc/init your viewController (lazily), the outlet to your textfield is pointing to nil.
The outlet doesnt get connected until your controller's view property is accessed, ie the view is displayed.
What you could do is give the settings viewController a handle to your calculating viewController and let it set a public property on the calculating viewController that represents the rate.
This is a common pattern - delegation - where one viewController (settingsViewcontroller) calls a method on its delegate (calculating viewController).
You wouldn't need the settingsViewcontroller property in your calculating viewController then, but just instantiate a new settings viewController every time you want it to be brought up, giving it a reference to your calculating viewController.
Another possibility - maybe even better - is to define a model object that does calculation and takes care of the rate it needs to calculate. Then you could give your settingsViewcontroller a reference to that model object (probably instantiated in your
other viewController), so that it can change the rate on it.
PS: also re think how you instantiate viewControllers generally. The designated initialiser is -initWithNibName:bundle: - so usually, you wouldn't just alloc/ -init them.
If you use storyboards (you probably should!), use storyboard's -instantiateViewControllerWithIdentifier: or use the above mentioned designated initialiser.
I want to access the RootViewController of my App in one of its classes in order to present a modal view controller. I do this by getting the ApplicationDelegate and asking it for the RootViewController and store it in a UIViewController
AppDelegate *appDelegate = (AppDelegate *) [UIApplication sharedApplication].delegate;
UIViewController* presentingViewController = appDelegate.viewController;
In my opinion this should work without a warning as RootViewController inherits from UIViewController. However I receive this warning:
Incompatible pointer types initializing 'UIViewController *__strong' with an expression of type 'RootViewController *'
Can someone explain to me why I see this warning?
If it helps - this is the AppDelegate where I define the RootViewController:
#interface AppDelegate : NSObject <UIApplicationDelegate> {
UIWindow *window;
RootViewController *viewController;
}
#property (strong) RootViewController *viewController;
I defined my RootViewController like this:
#interface RootViewController : UIViewController {
}
You can assign an object to a variable declared as its superclass. That is no problem and is very useful when you only want to use superclass methods over a set of your own subclasses, especially common with view controllers in a navigation stack when the specific type of next view controller is unknown.
Also think about it. Methods like
[self presentModalViewController:customController animated:YES];
wouldn't work without being able to do this. This method is declared as taking a UIViewController * but you pass in a custom UIViewController subclass with no complaints. Finally
[rootViewController isKindOfClass:[UIViewController class]];
will return YES. QED.
Have you forward declared your class RootViewController in the header for your app delegate?
i.e.
#class RootViewController;
#interface AppDelegate : NSObject <UIApplicationDelegate> {
....
Did you spell it correctly? This is a common area to mistype as xCode doesn't autocomplete forward declarations. It will then autocomplete your typo in the rest of the header file.
Did you remember to import the header file for your RootViewController into the .m file for the AppDelegate? You will still need to do that so the compiler knows about the inheretance.
Your code looks correct at the moment but we don't have all of it.
The problem is that RootViewController is not the same class as UIViewController.
In the AppDelegate, you declare viewController to be of type RootViewController. Then, in these lines:
AppDelegate *appDelegate = (AppDelegate *) [UIApplication sharedApplication].delegate;
UIViewController* presentingViewController = appDelegate.viewController;
You are creating presentingViewController, which is of type UIViewController, and setting it to an instance of RootViewController. This is the source of the error.
Fix this by using a consistent type.
Read What's the difference between the RootViewController, AppDelegate and the View Controller classes that I may create? for a nice explanation of the difference between these two types.
I have 2 view controllers now, And it both got tableviews.
When I choose a row in the second tableview (Using didSelectRowAtIndexPath),
and I want to pass the Information I got in the second View to the first View,
I tried to use delegate&protocol, but don't know why, It didn't work.
And I tried to use class method inside the first class, when I got variable in sencond View,
Call the class method inside the first class. The variable successfully pass to first View,
but when I want to set the Lable's text, it still failed..
Can somebody teach me how to do? thanks!
My protocol&delegate.
This is the second view.
#protocol CategoriesViewControllerDelegate;
#interface CategoriesViewController : UIViewController {
TableViewNewAppDelegate *appDelegate;
id <CategoriesViewControllerDelegate> delegate;
}
#property (nonatomic, assign) id <CategoriesViewControllerDelegate> delegate;
#end
#protocol CategoriesViewControllerDelegate <NSObject>
-(void)backstring:(NSString *)String;
#end
In the .m file , synthesize it
#implementation CategoriesViewController
#synthesize delegate;
didSelectRowAtindexPath
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
CategoryData *CateObj = [appDelegate.CateArray objectAtIndex:indexPath.row];
NSString *Strings = [NSString stringWithString:CateObj.CateTitle];
[delegate backstring:Strings];
[self.parentViewController dismissModalViewControllerAnimated:YES];
}
In the first view controller .h file.
#import "CategoriesViewController.h"
#interface DataController : UIViewController <CategoriesViewControllerDelegate>{
.m file
-(void)backstring:(NSString *)String {
NSLog(#"%#",String);
jCateField.text = String;
}
This is how I do my protocol+delegate. Are there something wrong?
btw, I created a Class method in the first view controller, and use the Class method in the sencond view controller, it succesfully pass variable to first view controller.
But the problem is, I can't set my Label's text inside my Class method, even calling Instance method to set text. Is there any way to solve this problem?
The code you provided seems to be correct. In your case you must set :
#property (nonatomic, assign) id <CategoriesViewControllerDelegate> delegate;
correctly to point to the first view controller which conforms to the protocol you defined :
#import "CategoriesViewController.h"
#interface DataController : UIViewController <CategoriesViewControllerDelegate>{
So it seems that you pushed a CategoriesViewController onto a first DataController, you probably missed to do so just before.
// self is the first view controller
// [myCategoriesViewController setDelegate:self]; old fashion
myCategoriesViewController.delegate = self;
[self presentModalViewController:myCategoriesViewController animated:YES];
This can probably solve your issue. Hope this helps.
Also consider let the first controller dismiss the second.
Here is a link to Apple's documentation.
You could just pass the information straight on to your second view controller;
SecondViewController.h
#interface SecondViewController
{
Information *info;
}
#property (nonatomic, retain) Information *info;
#end
SecondViewController.m
#implementation SecondViewController
#synthesize info;
...
#end
And in your didSelectRowAtIndexPath method;
SecondViewController *controller = [[SecondViewController alloc] initWithNibNamed:#"SecondViewController" bundle:nil];
[controller setInfo:YOUR_INFO_OBJECT];
[self.navigationController pushViewController:controller animated:YES];
[controller release];
Import second view controller header file in the first view controller implementation file. Import first view controller header file in second view controller header file.
Create the property (text/label/whatever) in the first view controller.
Create the property of first view controller in the second view controller.
Create the second view controller instance, set the first view controller property to what you need, push controller to the navigation controller. In the second view controller change whatever you want in the first view controller. Instance methods allowed. Do not forget to release first view controller.
Delegate pattern works in that way too.
View controllers are objects. Objects can have methods that can be called from other objects, and they can have instance variables. ("Delegate" is just a fancy term for this.)
There's no inherent reason why passing data between your view controllers should be hard or complicated, so long as the caller has the address of the callee. (And whether or not a given VC has an XIB is irrelevant.)
It sounds like your real problem is not knowing what to do with the data once it's been passed to the callee.
Stupid question: Is "jCateField" actually connected to the label you want to change, or is it nil? If you created the label from code (since you don't have an XIB), you will need to have stored the created label's address into "jCateField" during the view creation.
Can you post the code for as to ho you are displaying the contents when you come back to 1 st view controller.As here if the log gives you proper value then the issue is with the connection (if taken through iboutlet) or with addsubview .
Do you get nil in label or no value (label is hidden).
Okay, I've tried to figure this out over and over again.
I know the best practice is to have the App Delegate pass the managed object context to the first view controller in an application, and then have each subsequent view controller pass the managed object context down. However, when I'm using a Tab Bar Controller in my application, I can seem to wrap my head around that extra layer.
The only way I've been able to figure out how to do it is have the root view controller of each tab "Reach Back" into the app delegate to grab the context, but as I understand it this is poor form.
You can use interface builder to achieve the same thing.
Here is a slightly modified (for some additional clarity) version of Rog's original suggestion - notice the IBOutlet's
#interface AppDelegate : NSObject <UIApplicationDelegate> {
ViewController1 *vc1;
ViewController2 *vc2;
ViewController3 *vc3;
}
#property (nonatomic, retain) IBOutlet ViewController1 *vc1;
#property (nonatomic, retain) IBOutlet ViewController2 *vc2;
#property (nonatomic, retain) IBOutlet ViewController3 *vc2;
Then on the implementation file:
- (void)applicationDidFinishLaunching:(UIApplication *)application {
vc1.managedObjectContext = self.managedObjectContext;
vc2.managedObjectContext = self.managedObjectContext;
vc3.managedObjectContext = self.managedObjectContext;
// Continue with your implementation logic
}
Then from within Interface Builder ctrl drag from your App Delegate to the View Controller nested within the Tab Bar Controller and hook up the relevant View controller from the contextual menu that appears.
The key was, in the end, not to rely on interface builder to build the tab bar controller. By doing it manually in code I'm able to easily pass the managed object context to the view controller as I create them in applicatoinDidFinishLaunchingWithOptions:
I used this article as my basis: http://www.iphonelife.co.uk/creating-a-uitabbarcontroller-programmatically/
You can also just do something like this in your AppDelegate:
CoreDataUsingViewController *vc = (CoreDataUsingViewController *)[[tabBarController viewControllers] objectAtIndex:1];
vc.managedObjectContext = self.managedObjectContext;
I was adding coreData to an existing project with a few different build targets and didn't want to recreate all the different UITabBarControllers from scratch. It was pretty easy to do this way, though I'm not sure if it's the most artful way to do it or not.
See also
How to share a ManagedObjectContext when using UITabBarController
Not sure if I understand your issue correctly but why not simply pass the MOC to the other view controllers in the same manner? Here's an example:
#interface AppDelegate : NSObject <UIApplicationDelegate> {
ViewController1 *vc1;
ViewController2 *vc2;
ViewController3 *vc3;
}
// Declare properties as per normal
Then on the implementation file:
- (void)applicationDidFinishLaunching:(UIApplication *)application {
vc1.managedObjectContext = self.managedObjectContext;
vc2.managedObjectContext = self.managedObjectContext;
vc3.managedObjectContext = self.managedObjectContext;
// Continue with your implementation logic
}
I hope it helps!
Rog
Basically I have a viewController that loads at app startup. In that VC, depending on whether there is userdata, I serve up a ModalView with either a login. After the user logs in, I can then dismiss the modalView, but I would like to call a method on the opener that will then populate a table with data.
I thought from the modalView I could do something like
[self.parentViewController loadInitialData];
[self.dismissModalViewControllerAnimated:YES];
but that does not work..
any suggestions?
The problem is because self.parentViewController is of type "UIViewController" and your -loadInitialData method doesn't exist in UIViewController. There are a couple of common ways to solve this problem... from easiest and least "correct" to most complicated and most "correct":
1) First you need to cast your self.parentViewController to the type of your parent view controller. Something like:
MyParentViewController *parentVC = (MyParentViewController*)self.parentViewController;
[parentVC loadInitialData];
2) You can add a property to your modal view controller that explicitly keeps a reference to your parent view controller and then call loadInitialData doing that.
#interface MyModalViewController : UIViewController {
MyParentViewController *myParentViewController;
}
#property (nonatomic, retain) MyParentViewController *myParentViewController;
Then you can call:
[self.myParentViewController loadInitialData];
3) The most complicated, but most correct way to do it is to create a Delegate protocol, have your ParentViewController implement the protocol and have your modal view controller keep a reference to the delegate and call that way. Something like:
#protocol ManageDataDelegate
- (void) loadInitialData;
#end
#interface MyParentViewController : UIViewController <ManageDataDelegate> { ...
#interface MyModalViewController : UIViewController {
id<ManageDataDelegate> delegate;
}
#property (nonatomic, assign) id<ManageDataDelegate> delegate;
When you present your modal view controller, just set the delegate. In your MyParentViewController:
MyModalViewController *vc = [[MyModalViewController alloc] init];
vc.delegate = self;
[self presentModalViewController:vc];
Then in your modal view controller you can call back like so:
[self.delegate loadInitialData];