Variable lost after dismissing modalViewController - ipad

I'm using Reachability in my iPad app and discovered some issues when using modalViewControllers.
In my mainViewController I have a BOOL variable determining weather I'm online or not. Here's my code:
// mainViewController.h
BOOL online;
// mainViewController.m
- (void)reachabilityChanged:(NSNotification *)note
{
if([[note object] isReachable]) {
online = YES;
}
else {
online = NO;
}
}
- (void)getOnline
{
NSLog(#"%d", online);
}
// modalViewController.m
#import "mainViewController.h"
- (IBAction)dismissMe
{
mainViewController *main = [[mainViewController alloc] init];
[main getOnline];
[self dismissModalViewControllerAnimated:YES];
}
When I'm calling [self getOnline] within the mainViewController, it returns 1 ('cause I am online).
But: when I'm calling [main getOnline] within the modalViewController, it returns 0 in the log.
Does anybody know why?!
I also tried to put the online variable as a #property into the modalViewController to handle the if online stuff within the modal. But when I assign a value to it (from the main), and log it within the modal, it always returns (NULL).
Hope, you can help me! With best regards, Julian

Short answer: because they use different instances of the online variable.
Long answer: you should only declare BOOL online in the header, not define it. Defining should happen in the .m file, like this:
In the mainViewController.h:
extern BOOL online; // Declare the variable
In the mainViewController.m:
BOOL online; // Define the variable
// the rest of your code
The way your code is written, a separate BOOL online is created for each .m file that includes mainViewController.h; I am sure this is not what you intended.

Related

Changing Variable in another class iOS

I have follow countless similar situations on here ( stack overflow ). I have applied those write ups for my situation and have come close but haven't found a solution that seems work for me. As this is something very trivial I am baffled at how it isn't working for me.
Anyways, I am trying to set a Int variable from inside the appDelegate class and the variable actually belongs, if that is the right word, to another class (mainViewController).
For the MainViewController class .h file I have
#interface MainWindowControllerViewController :... {
int relayState;
}
#property (readwrite, nonatomic) int relayState;
For the MainViewController class .m file I have
#implementation MainWindowControllerViewController
#synthesize relayState = _relayState;
-(void)quickConnect { // Call for all UI bypassing and quick kill
NSLog(#"Relay state in MainWindow = %d", relayState);
if (_relayState == 1) {
NSLog(#"TURNING ON KILL SWITCH");
self.writeData = [[NSString stringWithFormat:#"%#", #"e"] dataUsingEncoding:NSASCIIStringEncoding];
[sensor write:sensor.activePeripheral data:writeData];
} else {
NSLog(#"TURNING OFF KILL SWITCH");
self.writeData = [[NSString stringWithFormat:#"%#", #"o"] dataUsingEncoding:NSASCIIStringEncoding];
[sensor write:sensor.activePeripheral data:writeData];
}
}
For the appDelegate.h file I have
#import "MainWindowControllerViewController.h"
#interface AppDelegate : UIResponder <UIApplicationDelegate>
{
MainWindowControllerViewController *relayState;
}
#property (nonatomic, assign) MainWindowControllerViewController *relayState;
Then for the appDelegate.m file I have
#import "MainWindowControllerViewController.h"
#implementation AppDelegate
#synthesize relayState = _relayState;
- (BOOL)application:(UIApplication *)application openURL:(NSURL *)url sourceApplication:(NSString *) sourceApplication annotation:(id)annotation {
NSLog(#" Calling application: %#", sourceApplication);
NSLog(#" URL scheme: %#", [url scheme]);
if ([sourceApplication isEqualToString:#"URL-Scheme-Test"]) {
if ([[url scheme] isEqualToString:#"TurnOffRelay"]) {
_relayState =[[MainWindowControllerViewController alloc] init];
_relayState.relayState = 1;
NSLog(#"Relay State BEFORE = %d", _relayState.relayState);
}
return YES;
if ([[url scheme] isEqualToString:#"TurnOnRelay"]) {
_relayState =[[MainWindowControllerViewController alloc] init];
_relayState.relayState = 0;
NSLog(#"Relay State BEFORE = %d", _relayState.relayState);
}
return YES;
}
else
return NO;
}
This is pretty much it. When I do the logs I find that the relayState that I want to change the value of shows that I was able to change the value. But when I do the If statement above that checks weather the relayState is equal to 1 the variable is always 0.
I'm not the most proficient in Obj C. Some help would be appreciated! Thanks. I'll gladly answer any extra questions about code if needed.
You are kind of mixing some older style obj-c with how it usually looks currently and I think you are hiding a variable (one declaration is hiding another)
Take out:
{
int relayState;
}
From your MainWindowControllerViewController interface
Take out the #synthesize in the MainWindowControllerViewController implementation
Don't use _relayState (just use relayState)
Do the same with the MainWindowControllerViewController variable in the AppDelegate.
If that doesn't fix it, we need to see what is happening to the VC you are creating.
The problem I believe is this line
_relayState =[[MainWindowControllerViewController alloc] init];
You are initializing MainWindowControllerViewController in both the if blocks which is resetting the value to the default value (In this case 0) every time.
UIStoryboard *storyboard = [UIStoryboard storyboardWithName:#"Main" bundle:nil];
MainWindowControllerViewController *vc = [storyboard instantiateViewControllerWithIdentifier:#"MainWindowControllerViewControllerIdentifier"];
vc.relayState = 1;
For the MainViewController class .h
#interface MainWindowControllerViewController :... {
int relayState; //remove this line
}
#property (nonatomic) int relayState; //use this
try this
You are making a mistake that will create endless problems for you.
You have a property named relayState and an instance variable named relayState.
The property "relayState" is backed by an instance variable named _relayState. You have another instance variable named relayState. Two different variables. Assigning to self.relayState changes one, assigning to relayState changes the other. Don't do it.
Just get rid of the "int relayState;" and don't use #synthesize and you'll be fine. At least a lot finer than you are now. You can then either use self.relayState or _relayState. At least you will always know what you are doing.
PS. Having an int relayState and a MainWindowViewController* relayState is just asking for trouble. You seem to be intentionally trying to confuse yourself.
PS. You seem to do the same dangerous game with the writeData property/variable.

iOS singleton viewDidLoad empty and on viewDidAppear not

I created a singleton in ios7 like this:
SharedData.h
#interface SharedData : NSObject
{
}
+ (id)sharedInstance;
#property (strong, nonatomic) NSMutableArray *list;
#end
SharedData.m
#import "SharedData.h"
#implementation SharedData
#synthesize list;
// Get the shared instance thread safe
+ (SharedData *)sharedInstance {
static dispatch_once_t once = 0;
static SharedData *sharedInstance = nil;
dispatch_once(&once, ^{
sharedInstance = [[self alloc] init];
});
return sharedInstance;
}
- (id)init {
self = [super init];
if (self) {
//initialize
list = [[NSMutableArray alloc] init];
}
return self;
}
#end
I always use this code to access this class:
SharedData *sharedData = [SharedData sharedInstance];
The problem is now when I switch the view in my viewDidLoad method the list is empty but in my viewDidAppear method everything is fine. Any ideas?
EDIT:
This is the code how I change the views:
SharedData *sharedData = [SharedData sharedInstance];
//clear feed and add new feed
[sharedData.list removeAllObjects];
[sharedData.list addObjectsFromArray:newList];
//show new gui
[self.navigationController performSegueWithIdentifier:#"goToMain" sender:self];
NOTE: I push from a normal ViewController to a TabBarController -> NavigationController -> TableViewController to display the list.
I guess you have the confusion between these two viewcontroller methods:
-(void)viewDidLoad{
//
}
&
-(void) viewDidAppear{
//
}
viewDidAppear is the method which is called each time your view changes but viewDidLoad is the method which is not necessarily called each time your view changes.
ViewDidLoad method is called when view loads for the first time, after that it doesn't get called until the views are removed/released.
P.S: I suggest you to put the breakpoint in your viewDidLoad and viewDidAppear method and feel it. Your answer lies there.
Hope this helps you alot.
Good Luck.
The problem was i created a segue which went from the button to the next view. Because of this the viewDidLoad gets earlier called than the list assigned. I just changed the segue to go from view to view.
How are you changing from one viewController to the other? Wich classes are the parents of your destination ViewController?,
If you are modifying properties of the view in the prepareForSegue method... you are forcing the view to load.
For example, you are setting the list of your singleton in prepareForSegue, but before setting the list you are modifying a property of your destination viewController. (doing something like destVC.view = XXX or destVC.viewControllers = XX if you are subclassing a UITabBarViewController...) Then you are triggering the viewDidLoad method , and it's executing before you have set the list to the correct value.
Or maybe you are seguing in two different places to the destinationViewController. And when the viewDidLoad happens, you still have not updated the list on the singleton.
Here is the transcription of the chat with the poster of the question: https://chat.stackoverflow.com/transcript/55218

Pass BOOL value

I am working on an app and I got stuck at the point where I can't seem to retrieve the value of a BOOL set in a class.
I spent too much time already on it, been through all the questions I found that seem to cover the matter.
The bad thing here is that I get something, but not what I need (I get a 0, which means, I guess, that the value wasn't retrieved correctly as it should be 1).
The things I tried are :
pass a pointer to my first class and access to my BOOL like this:
//in some method
self.pointerFirstClass.myBOOL;
NSLog(#"%d", firstClass.myBOOL); => This gives 0!
by declaring it (talking of the pointer) as a property in my second class (and importing the h. file from my first class, where my BOOL is declared as property too):
#property FirstClass *pointerFirstClass;
But I got 0 using this.
The other shot I gave was add my BOOL in the first class and create an instance of the class in my second class
//in some method
FirstClass *firstClass = [[FirstClass alloc] init];
if (firstClass.myBOOL){
//Do something
}
NSLog(#"%d", firstClass.myBOOL); => This gives 0!
But I got 0 too.
As Booleans are primitive types, like in C, I get a bit confused since I am new to object-oriented programming, I don't know how I could like create a getter for this, for example.
I also tried to do a - (BOOL)getBOOLValue method in my first class, and call this method in my second class and assign it to a BOOL in that second class.
But the result wasn't better.
Am I missing something?
Is there a way to get my value that I didn't think of or didn't know about yet?
I am running low on thoughts on how to get around this, it shouldn't be that hard IMO so I hope it is something simple that I just left aside.
EDIT :
Some actual code. I am working between 2 files called AppDelegate (yes, the actual one) and WelcomeViewController (so a VC).
AppDelegate.h
#interface AppDelegate : UIResponder <UIApplicationDelegate>
{
BOOL inRegion; //thought of this making my BOOL as a property of AppDelegate
}
#property (strong, nonatomic) UIWindow *window;
#property BOOL inRegion; //Declaring my BOOL here to make it accessible for another class
- (BOOL)getBOOLValue; //An attempt to pass my BOOL value
AppDelegate.m
- (void)locationManager:(CLLocationManager *)manager didDetermineState:(CLRegionState)state forRegion:(CLRegion *)region
{
if (state == CLRegionStateInside)
{
self.inRegion = YES; //Set my BOOL to TRUE
}
else if (state == CLRegionStateOutside)
{
self.inRegion = NO; //Else set it to False
}
- (BOOL)getBOOLValue
{
return inRegion; //Tried to create a custome "getter"
}
WelcomeViewControler.m (I changed nothing in the .h file)
I said I tried many things, right now, this is the last version of my code.
//Simply trying to do a Segue on a condition...
- (IBAction)onClick:(id)sender {
AppDelegate *appDelegate = [[AppDelegate alloc] init];
if (appDelegate.inRegion) {
[self performSegueWithIdentifier:#"WelcomeToDetection" sender:self];
}
else
{
//Do Nothing
}
}
As said, I want to retrieve the BOOL value of the AppDelegate.
Thank you.
This code doesn't make sense:
self.pointerFirstClass.myBOOL;
NSLog(#"%d", firstClass.myBOOL); => This gives 0!
The first line doesn't do anything. You're not assigning anything to the property, and you're not doing anything with the value. Furthermore, the second line doesn't relate to the first line in any way that we can see from the code you've provided. Try this instead:
self.pointerFirstClass = [[FirstClass alloc] init];
self.pointerFirstClass.myBOOL = YES;
NSLog(#"myBOOL = %d", self.pointerFirstClass.myBOOL);
In other words, you need to be sure that self.pointerFirstClass points to a valid object. And then you need to make sure that you've assigned the value you want to the myBOOL property of that object.
Update: This looks like a case where you're talking to the wrong object. Look at this:
- (IBAction)onClick:(id)sender {
AppDelegate *appDelegate = [[AppDelegate alloc] init];
This is surely not what you really want. The application object is a single object -- a real singleton, in fact, meaning that there is and can be only one application object. That object has a delegate object, and that's a specific instance of your AppDelegate class. In this code, though, you're creating a new instance of AppDelegate, one that's different from the one that the application is using. Any changes that are made to the actual application delegate in response to messages from the application will not be reflected in the new object that you've created.
What I think you want is to get the actual application delegate object, and you can do that using:
[[UIApplication sharedApplication] delegate];
So, change your code to look like this:
- (IBAction)onClick:(id)sender {
AppDelegate *appDelegate = (AppDelegate*)[[UIApplication sharedApplication] delegate];;
if (appDelegate.inRegion) {
[self performSegueWithIdentifier:#"WelcomeToDetection" sender:self];
}
// note: you don't need an else clause if it doesn't do anything
}
That way, you'll be talking to the same object that the app uses, which is the one that has the inRegion property set in response to the location manager call.
UPDATE - Now we can see your code the problem is obvious, you are trying to access the appDelegate by creating a new one...
- (IBAction)onClick:(id)sender {
AppDelegate *appDelegate = [[AppDelegate alloc] init];
Instead you should be doing this....
- (IBAction)onClick:(id)sender {
AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate]
--
Not sure if you are posting your actual code? but the first example you give...
self.pointerFirstClass.myBOOL;
NSLog(#"%d", firstClass.myBOOL); => This gives 0!
Shouldn't the second line be
NSLog(#"%d", self.pointerFirstClass.myBOOL);
Also this property...
#property FirstClass *pointerFirstClass;
Won't retain it once you've set it, it needs to be
#property (nonatomic,strong) FirstClass *pointerFirstClass;
In the second example...
FirstClass *firstClass = [[FirstClass alloc] init];
if (firstClass.myBOOL){
//Do something
}
NSLog(#"%d", firstClass.myBOOL); => This gives 0!
You allocate and initialise a new FirstClass object and then check the property straight away, if you are not setting this to YES in the init then it will be false
Like I say, maybe you're not posting your actual code?
I guess what you want is initializing myBOOL to 1.
If so, you need do something as following
#implement FirstClass
- (id)init
{
self = [super init];
if(self) {
_myBOOL = 1;
}
return self;
}
// Other methods
#end
EDIT:
The comments is why you get 0.
- (IBAction)onClick:(id)sender {
AppDelegate *appDelegate = [[AppDelegate alloc] init]; // this is the problem.
// you create a new appdelegate,
// and never call locationManager:didDetermineState:forRegion:
if (appDelegate.inRegion) {
[self performSegueWithIdentifier:#"WelcomeToDetection" sender:self];
}
else
{
//Do Nothing
}
}
rewrite your code as following:
- (IBAction)onClick:(id)sender {
AppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
if (appDelegate.inRegion) {
[self performSegueWithIdentifier:#"WelcomeToDetection" sender:self];
}
else
{
//Do Nothing
}
}

Pass data to segue destination without iVar

Since switching to storyboards, I load a view controller via
[self performSegueWithIdentifier:#"identifier" sender:self]
This works perfectly. Now, if I want to set any properties on the destination view controllers, I implement the method prepareForSegue:sender: and set what properties I need to set. Everything works as expected without any problems.
Ever since I starting using this approach over the old
MyViewController *vc = ....
vc.prop = #"value";
[self.navigationController pushViewController:vc];
I've felt that passing parameters to the destination view controller is a little hacky, in particular if the value you're trying to set is not just a static value.
Lets say for example, I have a button which fetches some data from a server. When the data returns, it creates a new object, and then presents a new view controller to display this object. To do this, I call performSegueWithIdentifier:sender:, but that's the end of it. My object is now deallocated and no longer exists, and I have no way of passing it to the prepareForSegue:sender: method, unless I store it in an instance variable.
This feels pretty horrible, as the object isn't meant to last longer than this action, and has no relation to anything else in my current view controller.
In this situation, I understand that I could quite simply request the data in the new view controller but it's just an example.
My question is, is there another way of doing this without it feeling so hacky? Can I get this data into the destination view controller without storing it in an instance variable?
I know I could still use the old approach, but I'd like to stick with the storyboard methods if I can.
Well the sender parameter of the performSegueWithIdentifier:sender is the same one received by the prepareForSegue:sender. So if you want to send a variable to your prepareForSegue:sender the sender is your friend. In your case:
SomeViewController.m
-(void)aMethodThatDownloadsSomeDataFromServer {
NSString *exampleData = [self someDataThatIDownloaded];
[self performSegueWithIdentifier:#"yourSegueIdentifier" sender:exampleData];
}
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if(segue.identifier isEqualToString:#"yourSegueIdentifier"]) {
if([sender isKindOfClass:[NSString class]]) { //maybe you want to send different objects
segue.destinationViewController.stringProperty = sender;
}
else {
segue.destinationViewController.objectPorperty = sender;
}
}
}
The accepted solutios is correct but I frequently use another approach when data are shared between more than two segue. I frequently create a singleton class (let's call it APPSession) and I use it as a datamodel, creating and maintaining a session-like structure I can write and read from everywhere in the code.
For complex applications this solution maybe requires too much error prone coding but I've used it succesfully in a lot of different occasions.
APPSession.m
//
// APPSession.m
//
// Created by Luca Adamo on 09/07/12.
// Copyright 2012 ELbuild. All rights reserved.
//
#import "APPSession.h"
#implementation APPSession
#synthesize myProperty;
static APPSession *instance = nil;
// Get the shared instance and create it if necessary.
+ (APPSession *)instance {
if (instance == nil) {
instance = [[super allocWithZone:NULL] init];
}
return instance;
}
// Private init, it will be called once the first time the singleton is created
- (id)init
{
self = [super init];
if (self) {
// Standard init code goes here
}
return self;
}
// This will never be called since the singleton will survive until the app is finished. We keep it for coherence.
-(void)dealloc
{
}
// Avoid new allocations
+ (id)allocWithZone:(NSZone*)zone {
return [self sharedInstance];
}
// Avoid to create multiple copies of the singleton.
- (id)copyWithZone:(NSZone *)zone {
return self;
}
APPSession.h
//
// APPSession.h
//
// Created by Luca Adamo on 09/07/12.
// Copyright 2012 ELbuild. All rights reserved.
//
#import <Foundation/Foundation.h>
#interface APPSession : NSObject{
}
#property(nonatomic,retain) NSString* myProperty;
+ (id)sharedInstance;
#end
How to read and write the property myProperty from every part of the app code.
// How to write "MyValue" to myProperty NSString *
[APPSession instance] setMyProperty:#"myValue"]
// How to read myProperty
NSString * myVCNewProperty = [[APPSession instance] myProperty];
With this mechanism I can safely write for instance a value in the APPSession in the first ViewController, perform a segue to a second one, perform another segue to a third one and use the variable written during the first segue.
It's more or less like a SessionScoped JavaBean in Java EE. Please feel free to point out problems in this approach.
All of these answers are correct, but I've found a pretty cool way of doing this. I've tested only in iOS 7 and iOS 8
After declaring and setting the value of the object you wish to pass, in the prepareForSegue method,
[segue.destinationViewController setValue:event forKey:#"property"];
//write your property name instead of "property

In iOS prevent RootViewController to become God like by extra 'controller' to display MFMailComposeViewController

I've asked a question about the same issue before, and the solutions worked, but it was not a compatible iOS 4.3 solution, and I thought my design is not the right one.
Now I want to show a MFMailComposeView(Controller) as a modal view on top of my RootView(Controller) when i press a button. And instead of making it the delegate i want to make a simple NSObject which implements the protocol.
Who is also capable to show the MFMailComposeView(Controller) in the RootViewController.
I am trying this design/solution which gives me memory allocation/access problems.
RootViewController.m:
- (IBAction)tapExportButton:(id)sender
{
SendMailController *sendMailController = [[SendMailController alloc]initWithParentViewController:self];
[sendMailController openMailDialog];
[sendMailController release];
}
SendMailController.h
#interface SendMailController : NSObject <MFMailComposeViewControllerDelegate>
- (id)initWithParentViewController:(UIViewController *)parentViewController;
- (void)openMailDialog;
#property (retain, nonatomic) UIViewController* parentViewController;
#end
SendMailController.m
#import "SendMailViewController.h"
#implementation SendMailController
#synthesize parentViewController = _parentViewController;
- (id)initWithParentViewController:(UIViewController *)parentViewController
{
if (self=[super init]) {
self.parentViewController = parentViewController;
}
return self;
}
- (void) dealloc
{
self.parentViewController = nil;
[super dealloc];
}
- (void)openMailDialog
{
if ([MFMailComposeViewController canSendMail])
{
MFMailComposeViewController *mailer = [[MFMailComposeViewController alloc] init];
mailer.mailComposeDelegate = self;
...
mailer.modalPresentationStyle = UIModalPresentationPageSheet;
[self.parentViewController presentModalViewController:mailer animated:YES];
[mailer release];
}
}
- (void)mailComposeController:(MFMailComposeViewController*)controller didFinishWithResult:(MFMailComposeResult)result error:(NSError*)error
{
switch (result)
...
// Remove the mail view
[controller.parentViewController dismissModalViewControllerAnimated:YES];
}
#end
When I set a breakpoint in the delegation method, it crashes already before that.
Is is something with the delegate property of mailer (MFMailComposeViewController)?
The problem is that you create your instance of SendMailController and try to show the composer view, and then you release the SendMailController. This causes it to be deallocated. It looks like it works because the composer view is on screen - this is because it has been retained by the presentModalViewController call.
To fix, you need to retain your instance of SendMailController and release it when the composer has been dismissed.
The correct way to do it (and required if you use ARC, and you should use ARC) is to provide a delegate callback to tell the owner that it's finished - which kind of makes the class pointless if all it does is wrap the composer.
The cheating way (which only works when not using ARC, and which you need to be very careful with) is to have your object retain itself when it presents the composer and release itself when the composer is dismissed.
The underlying problem being your root view controller containing all the logic, you should look at using child view controllers (if a single screen holds all your UI). Usually though, your root view should be the simple class (like a master list of options) and the views it presents would be more complex (the detail views). You need to look at ensuring that the appropriate class owns the responsibility for each screen of UI.

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