How to properly initialise controls in an instantiated view controller? - objective-c

Question

I have a class ErrorMessageViewController:
// ErrorMessageViewController.h
#interface ErrorMessageViewController: UIViewController {
NSString * tempTitle;
NSString * tempContent;
}
#property (nonatomic, strong) IBOutlet UILabel* messageTitle;
#property (nonatomic, strong) IBOutlet UILabel* messageContent;
-(void) initTitle:(NSString *)title andContent:(NSString *)content;
#end
// ErrorMessageViewController.m
#implementation ErrorMessage
#synthesize messageTitle, messageContent;
-(void) initTitle:(NSString *)title andContent:(NSString *)content {
tempTitle = title == nil ? #"" : title;
tempContent = content == nil ? #"" : content;
}
- (void) viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
if (messageTitle != nil) { [messageTitle setText:tempTitle]; }
if (messageContent != nil) { [messageContent setText:tempContent]; }
}
#end
And then I put it into display using this code:
NSString * errorMessage = #"Duplicate ID";
UIStoryboard * storyboard = [UIStoryboard storyboardWithName:#"Main" bundle:nil];
ErrorMessageViewController * errorMessage = (ErrorMessageViewController *)
[storyboard instantiateViewControllerWithIdentifier:#"ErrorMessage"];
[errorMessage initTitle:#"Error" andContent:contentVar];
[[self navigationController] pushViewController:errorMessage animated:YES];
When I debug it, on initTitle:Content:, the tempTitle and tempContent is NSCFConstString "Error" and NSCFString "Duplicate ID".
But then the flow goes to viewWillAppear, and both the tempTitle and tempContent 's contents are gone, replaced with NSCFString and NSObject. The tempTitle assignment is still OK because it's still string, though I don't know what the content is, but the tempContent assignment produce error. I can't even NSLog the tempContent value.
Why is this happened? Why the contents of the object change, like it was never initialised?

Answer 1

Set your data like this.
NSString * errorMessage = #"Duplicate ID";
UIStoryboard * storyboard = [UIStoryboard storyboardWithName:#"Main" bundle:nil];
ErrorMessageViewController * errorMessage = (ErrorMessageViewController *)
[storyboard instantiateViewControllerWithIdentifier:#"ErrorMessage"];
errorMessage.messageTitle = #"Error";
errorMessage.messageContent = errorMessage;
[[self navigationController] pushViewController:errorMessage animated:YES];
and use those variable directly in your viewDidLoad or viewWillAppear.
- (void) viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
// Use your variables
}
Edit :
-(void) initTitle:(NSString *)title andContent:(NSString *)content {
tempTitle = (title == nil ? #"" : title);
tempContent = (content == nil ? #"" : content);
}
NSString * errorMessage = #"Duplicate ID";
UIStoryboard * storyboard = [UIStoryboard storyboardWithName:#"Main" bundle:nil];
ErrorMessageViewController *vc = (ErrorMessageViewController *)
[storyboard instantiateViewControllerWithIdentifier:#"ErrorMessage"];
[vc initTitle:#"Error" andContent:errorMessage];
[[self navigationController] pushViewController:vc animated:YES];
Hope this will help

Answer 2

Storyboard is use lazy loading to load the subviews. messageTitle is not initialized after called instantiateViewControllerWithIdentifier. Call self.messageTitle to make the view initialized before set value.
ErrorMessageViewController * errorMessage = (ErrorMessageViewController *)
[storyboard instantiateViewControllerWithIdentifier:#"ErrorMessage"];
//tempTitle = nil
// [errorMessage initTitle:#"Error" andContent:contentVar];
[[self navigationController] pushViewController:errorMessage animated:YES];
// set value after push
[errorMessage initTitle:#"Error" andContent:contentVar];