I'm my class i've added a an instance of my view controller, created a property and then synthesized it in my implementation file. I am trying to update the UIlabel in the view controller like this,
NSString *currentChar = [[NSString alloc] initWithFormat:#"%c", ch];
viewController.outputLabel.text = currentChar;
[currentChar release];
My problem is that everything builds without any errors or warnings but the label just doesn't get updated, what am I doing wrong. I'd really appreciate some help on this one.
Are you sure you're referencing the existing viewController and you didn't instantiate a new one? Your property is not declared as copy, correct?
textProcessor.h / .m
#interface textProcessor : NSObject {
MainViewController *mainView;
}
#property (retain) MainViewController *mainView;
#end
#implementation textProcessor;
#synthesize mainView;
MainViewController.h / .m
#interface MainViewController : UIViewController {
UILabel *myLabel;
}
#property (retain) UILabel myLabel;
#end
#implementation MainViewController
#synthesize myLabel;
When you are initializing your textProcessor class, and you set the value for "mainView" like
-(void)viewDidLoad {
[super viewDidLoad];
textProcessor *proc = [[textProcessor alloc] init];
proc.mainView = self;
//note that you are not doing this:
//MainViewController *mainView = [[MainViewController alloc] init];
//proc.mainView = mainView;
//that was creating a new instance variable instead of using self, the existing one
[textProcessor release];
}
Have you created your label in IB? If you are using IB you have to create an IBOutlet for your UILabel. You then make a connection between the UILabel in IB to your IBOutlet in your class.
Have you tried calling the setNeedsDisplay method on the view? Also you may want to try using the setText method instead of assigning directly to the property.
Related
I'm having some trouble understanding how variable values are passed from one view to another. I have a UITextField in the firstview that the user enters a number into. When the user taps a button, that number is multiplied by 2 and the result is displayed on a UILabel in the second view. This is what I have thus far
FirstViewController.h
#interface FirstViewController : UIViewController{
UITextField *numberTextField;
NSNumber *aNumber;
}
#property (nonatomic, retain) IBOutlet UITextField *numberTextField;
#property (nonatomic) NSNumber *aNumber;
-(IBAction)calculate;
#end
FirstViewController.m
#implementation FirstViewController
#synthesize numberTextField, aNumber;
-(double)doubleNumber{
double number = [numberTextField.text doubleValue] * 2;
return number;
}
-(IBAction)calculate{
self.aNumber = [NSNumber numberWithDouble:[self doubleNumber]];
}
//more default code continues below
SecondViewController.h
#import "FirstViewController.h"
#interface SecondViewController : FirstViewController{
UILabel *numberLabel;
}
#property (nonatomic, retain) IBOutlet UILabel *numberLabel;
#end
SecondViewController.m
#implementation SecondViewController
#synthesize numberLabel;
- (void)viewDidLoad
{
[super viewDidLoad];
numberLabel.text = [NSString stringWithFormat:#"%#",aNumber];
}
Best and Easy Way to store value globally
set you object with your keyword
[[NSUserDefaults standardUserDefaults] setObject:#"Ajay" forKey:#"name"];
than get that object any where in you project
NSString *name = [[NSUserDefaults standardUserDefaults] objectForKey:#"name"];
You should accomplish what you want by using a segue. Create a segue in your storyboard and then call it in your firstviewcontroller with - (void)performSegueWithIdentifier:(NSString *)identifier sender:(id)sender. Then to pass data, import your secondviewcontroller.h file with a property for the value you want to pass and setup - (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender.
In that method you can pass things by using [segue.destinationViewController ###call the setter for the property in your secondViewController.h file###];
If this isn't clear, or you need more help just let me know.
I'm assuming that the FirstViewController is instantiating the SecondViewController. If that is so, then you just pass aNumber to the SecondViewController using an additional property:
// add an additional property to the SecondViewController
#property (nonatomic, retain) NSNumber *aNumber;
When you instantiate the SecondViewController inside the FirstViewController, you just pass that value to the SecondViewController before you load it:
// inside FirstViewController
SecondViewController *secondViewController = [[SecondViewController alloc] initWithNibName:#"SecondViewController" bundle:nil];
secondViewController.aNumber = aNumber;
// inside SecondViewController
- (void)viewDidLoad
{
[super viewDidLoad];
numberLabel.text = self.aNumber;
}
Mmm... Pay attention to not confuse views and viewControllers!!!
A viewController can manage more than a view. For example in your code you have a UITextField, a UILabel and probably a UIButton. These are all views that are managed by two viewsController (FirstViewController and SecondViewController).
As long as you have so few views to work with you can use just one viewController and pass the value you want to your UILabel directly:
- (void)calculateAndPassValue
{
aNumber = [NSNumber numberWithDouble:[self doubleNumber]];
numberLabel.text = [NSString stringWithFormat:#"%#",aNumber];
}
Otherwise, if your goal is passing variable values from one viewController to another. Well... There are many ways you can obtain that, for example:
Creating an ivar.
Using a singleton.
Saving your data in NSUserDefault.
Creating a database on disk.
First and second cases are good if you need to manage your data while your app is running. Third and fourth if you want to memorize your data for future use and retrieve them at next start up.
Try to search keys like ivar, singleton, NSUserDefault and you'll find many discussions and lines of sample code.
I'm setting a string in a view controller called ViewController and trying to access it somewhere else. This is the code:
ViewController.h
NSString *string;
...
#property (retain) NSString *string;
ViewController.m
#synthesize string;
...
-(void)viewDidLoad {
...
string = #"Test";
}
OtherViewController.m
#import "ViewController.h"
...
-(void)viewDidLoad {
ViewController *vc;
vc = [[ViewController alloc] init];
NSLog(#"String: %#", vc.string);
}
However, the log is showing: String: (null). What am I doing incorrectly? Thanks.
The viewDidLoad of ViewController is only called when the view is loaded. The view is lazily loaded when required e.g. when a call to vc.view is made.
I'm not sure what you are trying to achieve but this certainly seems like a code smell to me.
As #Fscheidl points out you are creating a new instance and not accessing an existing instance so this may add to your problem. I still believe your main issue is that you assume viewDidLoad is being called just by creating the viewController, which is not the case
edit : it doesn't necessarily need to be an NSObject class, if you want to, you could also do this on your viewController class, just be sure to also include
-(id)init
on your header
---- end of edit
if you're trying to make a class that's accessible to another view controller, why not try NSObject instead of view controller (considering you only need to take that string value)
for instance, lets call that viewController class "global" class
so at global.h, you put up
#import <Foundation/Foundation.h>
#interface GlobalVar : NSObject
#property (nonatomic, strong) NSString *myString;
-(id)init;
#end
and then, at global.m you put up
#import "GlobalVar.h"
#implementation GlobalVar
#synthesize myString;
-(id)init
{
self = [super init];
if(self)
{
myString = [[NSString alloc]initWithFormat:#"the String"];
}
return self;
}
#end
after this, everytime you need to access the "myString" object that contained in global class, you could put up
at header :
#import "GlobalVar.h"
...
...
#property (nonatomic, strong) GlobalVar *globalVar;
at implementation file :
#synthesize globalVar;
...
...
self.globalVar = [[GlobalVar alloc]init];
NSString *theString = globalVar.myString;
NSLog(#"content of my string is : %#",theString);
there you go ;)
You do create a new instance of ViewController by calling [[ViewController alloc] init]; This instance hasn't had string even set. You have to access that exact instance of ViewController.
If you create the instance of OtherViewController directly from ViewController, you can add the following to OtherViewController.h:
#import "ViewController.h"
#property (nonatomic, retain) ViewController *previousViewController
When creating the OtherViewController, you can then set:
//alloc and init instance of OtherViewController
myOtherViewController.previousViewController = self;
In your viewDidLoad: method, you can then access your string as follows:
NSLog(#"String: %#", previousViewController.string);
I am passing an NSDictionary object from one view class to another as I transition from a table view to a normal view to show details:
Passing Controller:
[tweetController setTweet:tweet];
Receiving Controller.h:
#interface TweetViewController : UIViewController {
NSDictionary *tweet;
}
#property (nonatomic, retain) NSDictionary *tweet;
Receiving Controller.m:
#implementation TweetViewController
#synthesize tweet = _tweet;
I then try to use this information to set the properties of some fields in my view:
- (void)viewDidLoad
{
[super viewDidLoad];
tweetLabel.text = [_tweet objectForKey:#"text"];
}
The result is a blank label and if I inspect the value of _tweet at this stage it is nil.
I originally had a method which set the value of tweet which I called at the same location as I am now setting the value. If I inspected the value at this stage it was fine.
I presume that the automagic setter through #synthasize is working, but somewhere else the value is being lost.
Sorry this is my first objective C anything! Thanks for any help in advance.
You are using your "tweet" instance variable, whereas the "tweet" property is synthesized to the "_tweet" variable.
You are probably calling the setTweet method after viewDidLoad executes.
I usually pass this kind of thing into a custom init method.
Alternatively, you could do the set before pushing the detail VC onto the nav stack.
Are you sure that tweetLabel isn't nil?
I've made a few corrections & optimisations to your code. You don't need to declare ivars in the header file anymore, they are generated automatically by #synthesize
- (void)dealloc; is only needed if you're not using ARC.
//.h
#interface TweetViewController : UIViewController
#property (strong, nonatomic) NSDictionary *tweet;
#property (strong, nonatomic) IBOutlet UILabel *tweetLabel
#end
//.m
#implementation TweetViewController
#synthesize tweet = _tweet;
#synthesize tweetLabel = _tweetLabel;
- (void)viewDidLoad {
[super viewDidLoad];
self.tweetLabel.text = [self.tweet objectForKey:#"text"];
}
- (void)dealloc {
[_tweet release];
[_tweetLabel release];
[super dealloc];
}
#end
Note: strong is equivalent to retain
To expand on #Rayfleck's answer, since you are new to Objective-C, your custom init method could look like this:
In TweetViewController.h:
- (id)initWithTweet:(NSDictionary*)tweet;
In TweetViewController.m:
- (id)initWithTweet:(NSDictionary*)tweet
{
self = [super init];
if (self) {
_tweet = tweet;
}
return self;
}
and then in your passing controller you'd allocate and initialize like this:
TweetViewController *tvc = [[TweetViewController alloc] initWithTweet:myTweet];
I have my ViewController.h/m and another class Keyboard.h/m.
In my ViewController.h I have an UILabel:
#interface ViewController : UIViewController{
UILabel *label;
}
#property (nonatomic, retain) IBOutlet UILabel *label;
and my ViewController.m looks so
#import "ViewController.h"
#synthesize label;
...
Now I want to change the label from Keyboard.m.
I have tried something like this:
#import "ViewController.h"
...
ViewController *vc;
vc.label.text = #"text";
it compiles without any errors but the label doesn't change
It's very error prone that you're doing here.
ViewController *vc;
declares a pointer, but this won't be initialized; so when you're accessing its property vc.label.text, objc_messageSend() will be passed a bogus pointer, so it can potentially crash! (you're lucky if id didn't do so.)
Anyways: if you have done it well, like ViewController *vc = [[ViewController alloc] init]; creating a new instance wouldn't have affected the other instance. You have to store the pointer to your instance somewhere, e. g. set a #property (retain) ViewContrller *vc; to your application's app delegate object, and access it through that property like this:
[(MyAppDelegate *)[[UIApplication sharedApplication] delegate] vc].label.text = #"new text";
that way it should work.
Hope it helps.
How are you initiating your vc variable? I am guessing that is where the error is coming from. Try doing:
vc = [[ViewController alloc] initWithNibName:# ViewController"];
If you are already doing that, make sure your IBOutlet is hooked up correctly. You are setting the variable correctly so the error must be coming from somewhere else.
Im new to iphone development and after lots of reading on it im still trying to figure out how UIViews operate properly. I have been playing about with it and i this is where i am at so far:
I have created a new xcode project using the view-based application. I have my MMAppViewController classes and i created a new UIViewController subclass called "Level1View".
There is a button titled "Level 1" that takes me to the "Level1View" viewController. In this viewController there is there is a "next" button, a "main menu" button (that returns to MMAppViewController) and there is a label, currently titled "Level 1".
My problem is that the code i have used to change the title of label does not work! Does anyone know why this is? Here is my code:
#class MMAppViewController;
#interface MMAppAppDelegate : NSObject <UIApplicationDelegate> {
UIWindow *window;
MMAppViewController *viewController;
}
#property (nonatomic, retain) IBOutlet UIWindow *window;
#property (nonatomic, retain) IBOutlet MMAppViewController *viewController;
#end
and
#implementation MMAppViewController
-(IBAction)pushLevel1{
Level1View *level1View = [[Level1View alloc] initWithNibName:nil bundle:nil];
[self presentModalViewController:level1View animated:YES];
}
...
and
#import <UIKit/UIKit.h>
#interface Level1View : UIViewController {
IBOutlet UILabel *labelTitle;
}
-(IBAction)pushBack;
-(IBAction)pushNext;
#end
and
#import "Level1View.h"
#import "MMAppViewController.h"
#implementation Level1View
-(IBAction)pushBack{
MMAppViewController *MainView = [[MMAppViewController alloc] initWithNibName:nil bundle:nil];
[self presentModalViewController:MainView animated:YES];
}
-(IBAction)pushNext{
[labelTitle setText:(#"Thanks for playing :)")];
}
- (void)didReceiveMemoryWarning {
...
Currently the app runs but the label wont change when i hit the "next" button. Can anyone help?
are you sure a UINavigationController isn't a better tool for the job you want to do? That will make it easy for you to manage a stack of UIView objects.
That said, have you tried adding logging to make sure your pushNext method is getting called? where is labelTitle declared? Did you use a XIB or not?
Did you bind the Label in Interface Builder to the labelTitle outlet in your Level1View?
If you forget that step, the outlets won't work. Even after several years, I still forget this step sometimes.
--Mike
are you sure you connected the label in IB?
and if you set a property "#property (nonatomic, retain) IBOutlet UILabel *labelTitle;" in Level1View.h you can access it from Main View:
Level1View *level1View = [[Level1View alloc] initWithNibName:nil bundle:nil];
[self presentModalViewController:level1View animated:YES];
level1View.labelTitle.text = #"something";
[level1View release];
The other thing you shouldn't present the Main View Controller again instead dismiss the Level1View with:
#implementation Level1View
-(IBAction)pushBack{
[self dismissModalViewControllerAnimated:YES];
}
//
and maybe the problem is [[Level1View alloc] initWithNibName:nil bundle:nil] you have to specify the nib you want to load e.g. [[Level1View alloc] initWithNibName:#"Level1View" bundle:nil]
Declare labelTitle as a property in your header file, and synthesize labelTitle in your .m - as long as labelTitle is hooked up through interface builder the rest of your code is fine.
.h
#property (nonatomic, retain) IBOutlet UILabel *labelTitle;
.m
#synthesize labelTitle;
Then your setter call will work. (also, dot-notation works for synthesized properties so you may as well use it)
change
[labelTitle setText:(#"Thanks for playing :)")];
to
labelTitle.text = #"Thanks for playing :)";
Synthesizing a property will create setter and getter methods at runtime. Read: The Objective-C Programming Language