I have a couple classes that pass around a string through conditionals. In the end, a View Controller catches it and sets it to the text of a label that it owns. Most of it works so far, however, the label text isn't changing. But through NSLog, I can see that the ViewController is seeing the right string.
'.h'
#interface ViewController : UIViewController
{
}
#property (strong,nonatomic) IBOutlet UILabel *theLabel;
#property (strong,nonatomic) NSString *theString;
-(void)setLabelText:(NSString*)someString;
.m
-(void)setLabelText:(NSString*)someString {
NSLog(#"VC:%#",someString); //writes out the desired string fine!
theLabel.text = someString; //doesn't display the text
}
I know that the label works properly because I can call the "setLabelText:" method from viewDidLoad, and enter some random string, and it will show up. However, I can't seem to change it from this method. Any help would be appreciated.
"sender"
-(void)sendToMain:(NSString*)string{
ViewController *newController = [ViewController alloc];
[newController setLabelText:string];
}
Your problem lies in the fact that you are creating a new ViewController object, and trying to change a variable on an existing object. If you would like to access your ViewController from a different file, set up the ViewController as a delegate to your other class. Then call the delegate function to set the label's text.
Here is a tutorial on how to use delegates.
Also, note that only the main thread can make changes to the User Interface. So if you are unsure if the thread executing the conditionals is the main thread, you can add the following code.
dispatch_async(dispatch_get_main_queue(), ^{
//your code block here
});
I hope this helps.
Related
I am trying to do the following, and not able to find a straightforward answer.. It is related to this :Passing uitextfield from one view to another. But not exactly.
I have a Firstview.m, from which I push to a Secondview.m. The Secondview.m has a UITextView. I allow the user to edit the UITextView on Secondview.m. Now I want to store this text value in a variable in Firstview.m. One way to to do this is as follows
in Firstview.h
#property (nonatomic) Secondview *secondView;
That is keep a secondView variable in Firstview itself. But this doesn't seem efficient. Ideally I should only have 1 NSString text field in FirstView. What is the right way to do this ? Thanks
You can achieve this by using Delegation in Objective-C.
In your SecondView.h add following right after Header Inclusion
#protocol YourDelegateName <NSObject>
-(void)setText:(NSString *)strData;
#end
Also add delegate property to your header for accessing them in calling class, like below (This goes with other properties declaration in SecondView.h file):
#property (nonatomic, weak) id<YourDelegateName> delegate;
Now, Comes the calling the delegate part. Say, you want to save the text value of UITextView of SeconView in strTextViewData of FirstView class, when the following event occurs:
- (IBAction)save:(id)sender
{
[self.delegate setText:self.txtView.text]; // Assuming txtView is name for UITextView object
}
Now, In FirstView.h add YourDelegateName in delegate list like below:
#interface FisrtView : ViewController <YourDelegateName>
#property (nonatomic, reatin) NSString *strTextViewData;
#end
And then in FisrtView.m file when you create instance of SecondView class, set delegate to self like below:
SecondView *obj = [[SecondView alloc] initWithNibName:#"SeconView" bundle:nil];
obj.delegate = self; // THIS IS THE IMPORTANT PART. DON'T MISS THIS.
Now, Implement the delegate method:
-(void)setText:(NSString *)strData
{
self.strTextViewData = strData;
}
Applying this to your code will do what you want. Also, Delegation is one of the most important feature of Objective-C language, which - by doing this - you will get to learn.
Let me know, if you face any issue with this implementation.
Newbie question for Xcode gurus...
I have two views. They both use the same custom class. In view_1 I have a button and when this is pressed view_2 will show. In view_2 I have a label which will have it´s text changed when I press the button in view_1. As of now the Label_1 is nil when I set a breakpoint at it and therefor useless. How can I get to update this label when I press the button? Her are some snippets from my code...
This is my .h file:
#interface ViewController : UIViewController
{
IBOutlet UIButton *buttonSelectTimeInterval;
IBOutlet UILabel *labelTimer;
}
#end
This is the button action in my .m file:
- (IBAction)startPouring_ButtonClick:(id)sender
{
labelTimer.text = #"foo";
}
…but my .m file doesn't seem to know the labelTimer since it is a ´nil´. Why is this so? It is instantiated in the .h file.
Anyone?
You can use NSNotificationCenter. Put this in you IBAction.
[[NSNotificationCenter defaultCenter] postNotificationName:#"buttonPressed" object:nil];
And this to your viewDidLoad.
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(selectorhere) name:#"buttonPressed" object:nil];
somewhere in your .m
(void)selectorhere {
labelTimer.text = #"foo";
}
You can use NSNotificationCenter for this.
Here are the apple documentation link.
First, nothing is "instantiated" in the .h file - that's just the public listing of what properties and methods are available to other classes. Think of the header file as a table of contents, but only for the things the class wants others to see.
Those properties don't exist in memory until the instance of the class itself is created, and then only if you set them to some initial value once they're needed.
How & where are you creating the 2nd view? Is it a storyboard segue or something? The 1st view doesn't seem to have any way of knowing the 2nd one exists, so it won't be able to see or access the label.
View1Class.m
#import View2Class.h
#implementation View1Class
- (IBAction)startPouring_ButtonClick:(id)sender {
//Instantiate the 2ndView when you need it.
// This gives View1 a reference to View2 and its public UILabel.
View2Class * my2ndView = [[View2Class alloc] init];
my2ndView.labelTimer.text = #"foo";
}
#end
As I said, it's still not clear how/where you're actually displaying the 2nd view though, so the snippet above is incomplete. You could use a modal w/a delegate, or this is where NSNotificationCenter is a helpful option - the 2nd view can sign up to get notifications & change accordingly. There are numerous tutorials about creating a 2nd/modal view and displaying it on a button click - you should probably look at those to clarify how the structure of such an app ought to work.
This answer should get you on the right track.
Other specific issues:
Why is the label nil? Because there isn't one...
In this IBAction, which seems to be in View 1:
- (IBAction)startPouring_ButtonClick:(id)sender
{
labelTimer.text = #"foo"; //this is looking for labelTimer in the clicked view.
}
... it is looking for its own labelTimer IBOutlet (in which case it should probably be self.labelTimer.text), and not that of the 2nd view. If the 1st view doesn't even have a UILabel IBOutlet, this is another problem.
If the views have different functions & different properties, they probably shouldn't be instances of the same custom class. If the 1st view doesn't have or need a UILabel, it shouldn't have one in its .h. If the 2nd view doesn't have or need a button it shouldn't have one in its .h. If the views serve different purposes, then make them different classes.
BTW,
Since you're using instance variables for your IBOutlets, you'd need to write your own getter & setter methods if you want to change their values. Did you? To make those values accessible to other classes, you'd need to make those methods public & put them in the .h. It's not good practice for an instance to set its instance variables directly w/o a getter/setter, and other objects definitely should not.
The preferred method is to use #properties for your IBOutlets instead of declaring them as instance variables. This will automatically create the getter & setter methods, backing store in memory, and as of XCode 4.4 it automatically adds #synthesize so you no longer need to do so. Declaring your IBOutlets as "weak" references prevents retain cycles & memory leak, where the view holds on to the outlets & the outlets hold on to the view & nothing ever goes away...
View1Class.h
#interface ViewController : UIViewController
#property (nonatomic, weak) IBOutlet UIButton *buttonSelectTimeInterval;
#end
View2Class.h
#interface ViewController : UIViewController
#property (nonatomic, weak) IBOutlet UILabel *labelTimer;
#end
I have custom UIButton which programmatically interacts (triggers) with ViewController methods via protocol. But the behaviour of the button has to be dependent on the ViewController placed on. I do this to minimise amount of code in ViewControllers itself, as the button has to remain the same and bear the same functions (navigation).
Is there any way in UIButton's custom class to get the ViewController it is placed on?
I'd follow #rmaddy advice in a specific way, borrowing from the SDK's style
// MyCutomButton.h
#protocol MyCustomButtonDatasource;
#interface MyCustomButton : UIButton
#property(weak,nonatomic) IBOutlet id<MyCustomButtonDatasource>datasource;
// etc
#end
#protocol MyCustomButtonDatasource <NSObject>
#optional
- (NSString *)howShouldIBehave:(MyCustomButton *)button;
#end
Now the button can have it's datasource set in IB. View controllers that include it will need a little additional code (sorry, it's unavoidable in a good design). They will declare themselves as implementing MyCustomButtonDatasource.
When MyCustomButton needs to behave conditionally based on where it's placed, it can ask its datasource...
// MyCustomButton.m
NSString *string = #"defaultBehavior"; // per #RichardTopchiy's suggestion
if ([self.datasource respondsToSelector:#selector(howShouldIBehave:)])
string = [self.datasource howShouldIBehave:self];
// string is just made-up here, have it answer something simple (int, BOOL)
// that lets the button proceed with the right behavior. Don't ask for
// anything that relies on specific knowledge of how MyCustomButton
// is implemented
EDIT - To create the relationship, if you've decorated the property as an IBOutlet (as shown above), you should be able to setup the relationship in IB. Declare your view controller as implementing <MyCustomButtonDatasource>. Select your custom button, then the connections inspector, then drag to your view controller.
Alternatively, make the button itself an IBOutlet property in the view controller and, in viewDidLoad, do:
self.customButton.datasource = self;
The last way to do it is give your button a tag, say, 128, then:
MyCustomButton *customButton = (MyCustomButton *)[self.view viewWithTag:128];
self.customButton.datasource = self;
So I have this little project in which the user goes from one view to another as they click buttons, and the text on the last button they've clicked should show up in a label in the top of the screen. I figured out how to have the variables accessible from anywhere in the app, and also how to change it as the user presses the buttons. Yet, I can only make the label's text change once a button is hit, and I wanted it to happen automatically (the view to appear with the label already containing the correct text).
For that I set the label in two different ways (which I found online):
#interface ViewMateria : UIViewController
{
IBOutlet UILabel *materiaLabel;
}
#end
and
#interface ViewMateria : UIViewController
#property (weak, nonatomic) IBOutput UILabel *materiaLabel;
#end
Still, for both of this I can not access the label by a simple materiaLabel.text or anything like that, and can't find a way to do it without the need for the press of a button.
I've been looking for an answer for this for a while now, and nothing that I found seemed to be of use for me (since most of the links I found taught how to change a label text with the press of a button).
This is my first project with Objective-C and Xcode, and I don't really know the answer, so maybe I am missing something quite obvious, but still, if anyone could point me in the right direction, that would be of much help.
Put this in your .h file for the view controller:
#property (weak, nonatomic) IBOutput UILabel *materiaLabel;
When you are about to present the view controller, access it like this:
your_ViewMateria_object.materiaLabel.text = #"";
Then present it..
Are you using segues?
If yes, its another story..
UPDATE:
For segues use this, with the .h property value I just mentioned:
-(void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
ViewMateria *vm = [segue destinationViewController];
vm.materiaLabel.text = #"Whatever";
}
You should be good to go now ;D
Did it work?
UPDATE
In second view controller .h file
#property (strong, nonatomic) NSString *buttonName;
.m file
self.materiaLabel.text = self.buttonName;
In first view controller .m file
inside IBAction
secondviewcontrollerObject.buttonName = [(UIButton *)sender currentTitle];
This is what I got so far.
mainview.m
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender(id)sender {
secondView *secView = [segue destinationViewController]
secView.ext = #".com";
}
secondView.h
#interface secondView : UIViewController {
NSString *ext;
}
#proper (nonatomic, retain) NSString *ext;
#end
secondView.m
-(void)viewDidLoad {
NSString *url = [#"www.google" stringByAppendingFormat:ext]
}
And its returning a error saying ext is null... what am I doing wrong?
Did you try to turn ext into a property instead? My understanding is that the "dot" notation essentially turns your code into
[secView setExt:#".com"]
So turn SecondView.h into
#interface secondView : UIViewController
#property (nonatomic, copy) NSString *ext;
#end
And don't forget to #synthesize it in your .m file
Check the followings:
Make sure #synthesize ext; is in SecondView.m
In Storyboard, have you linked the segue correctly?
In Stodyboard, is the viewController that represetns SecondView defined as a class of SecondView?
Make sure that you are calling the SecondView via prepareForSegue:sender method (i.e. SecondView doesn't get called by pushViewController:animated somewhere else in your code).
Put a breakpoint at the line:
secView.ext = #".com";
and make sure that the ext ivar is properly set after the assignment. If it's not, you might be specifying that the accessors use a different ivar in your #synthesize directive for ext, or you might have provided a setter -setExt: that doesn't properly set the ivar.
If ext is set properly after the assignment, perhaps you've got two different instances of secondView. That used to happen a lot when people used .xib files -- they'd create one view controller in code and have another instance of the same class in their .xib file. I wouldn't expect that to be the case here since you're getting secView straight from the segue, but it's worth thinking about.
There are two views: view1 and view2.
Add view2.h file in view1.h
init object of view2 and set their variable.