Question

I have a textViewController class. I want to set(basically update) the corresponding textView’s content from another view controller which I am pushing over the present textViewController. The way I thought I could do this was to have a shared singleton class and have a string property there to contain the text. I have been using the singleton for storing some other content as well and it worked fine till now.

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But the text variable in singleton class doesn’t hold the content I pass to it from the second view controller and hence the textViewController, after popping the second view controller, displays the old text even after reappearing. I am updating the textView in its viewWillAppear method which is getting called but shows old text content on NSLogging.
What am I missing here? Please suggest a solution, stuck at it for a long time now.

Answer 1

Declaration

Firstly, declare the NSString in your app delegate .h file. It should look something like this:

//YourAppDelegate.h

#import <UIKit/UIKit.h>

@interface YourAppDelegate : NSObject < UIApplicationDelegate >
{
    NSString *sharedString; //WE ADDED THIS
}

@property (nonatomic, retain) NSString *sharedString; //AND THIS
@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) IBOutlet SomeViewController *viewController;

@end

Now you want to synthesize the object so that the accessor and mutator methods are made for you. This means you don’t have to write the setSharedString: and getSharedString methods – we can simply access and mutate the object by making a reference to it. This is how we synthesize it in the .m file:

//YourAppDelegate.m
@synthesize sharedString;

Assigning a Value

When you want to assign a value to sharedString from another class, you must first retrieve the active instance of your application delegate:

YourAppDelegate *appDelegate = (YourAppDelegate*)[[UIApplication sharedApplication] delegate];

The appDelegate object here is your running app delegate instance. To access the sharedString NSString object in the delegate and assign a value, we’d do this:

appDelegate.sharedString = @"some string we want to assign";

For the duration of our application’s runtime, “some string we want to assign” is now stored in sharedString in our app delegate.

Retrieving the Value

You’ll want to retrieve the value at some point. To do this, again we’ll have to get the running instance of our application delegate:

YourAppDelegate *appDelegate = (YourAppDelegate*)[[UIApplication sharedApplication] delegate];

Once we have the running instance, we can then access the sharedString object stored inside it:

NSString *retrievedString = appDelegate.sharedString;

From this point, retrievedString now holds the value “some string we want to assign“.

Note:

Everywhere I mention YourAppDelegate, I am referring to your app delegate – the app delegate you have in your project. It’ll be related to your project name (look for the file).