Problem with a NSString that equals to (null) - iphone

Question

I have an UIViewController named MainViewController
I have another UIViewController named LeftSharingViewController;
I would like to get and use the NSString from MainViewController in my LeftSharingViewController
I have a problem, I always get (null) instead of the NSString wanted value.
Here's my code and how does the NSString get it's value
MainViewController:
- (void)webViewDidFinishLoad:(UIWebView *)webView {
leftWebViewString = [NSString stringWithString:leftWebView.request.URL.absoluteString];
}
LeftSharingViewController.h:
#import <UIKit/UIKit.h>
#import "MainViewController.h"
#import <MessageUI/MessageUI.h>
#import <MessageUI/MFMailComposeViewController.h>
#class MainViewController;
#interface LeftSharingViewController : UIViewController <MFMailComposeViewControllerDelegate> {
MainViewController *mainViewController;
NSString *leftWebViewUrl;
}
#property (nonatomic, retain) MainViewController *mainViewController;
#property (nonatomic, retain) NSString *leftWebViewUrl;
#end
LeftSharingViewController.m:
#import "LeftSharingViewController.h"
#import "MainViewController.h"
#implementation LeftSharingViewController
#synthesize mainViewController;
#synthesize leftWebViewUrl;
- (void)viewWillAppear:(BOOL)animated {
self.leftWebViewUrl = self.mainViewController.leftWebViewString;
}
#pragma mark -
#pragma mark Compose Mail
-(void)displayComposerSheet
{
MFMailComposeViewController *mailPicker = [[MFMailComposeViewController alloc] init];
mailPicker.mailComposeDelegate = self;
[mailPicker setSubject:#"Check Out This Website!"];
[mailPicker setMessageBody:[NSString stringWithFormat:#"Take a look at this site:%#", leftWebViewUrl] isHTML:YES];
mailPicker.modalPresentationStyle = UIModalPresentationFormSheet;
[self presentModalViewController:mailPicker animated:YES];
[mailPicker release];
}
Thanks!

Answer 1

On your MainViewController, you are never retaining the NSString you create. You are using stringWithString:, which returns an autoreleased object.
You should either retain it, or (easier) change your code to use your accessor, which already retains, like this:
- (void)webViewDidFinishLoad:(UIWebView *)webView {
self.leftWebViewString = [NSString stringWithString:leftWebView.request.URL.absoluteString];
}
As a side note, if you are navigating from MainViewController to LeftSharingViewController, instead of "pulling" the data in LeftSharingViewController from MainViewController, I would do it the other way around:
In MainViewController, before displaying the view of LeftSharingViewController, I'd set the required properties.