Question

I’m new to Objective-C and iPhone SDK development. I want to call a method in the same class:

- (void) setFilePath:(NSString *) p
{
  [self methodCall];
}

- (void) methodCall
{
  fileContent.text = @"Test"; //fileContent is a UITextView
}

If the property “filePath” is set, the method “setFilePath” is called. Then the UITextView, created in IB, should display the text. But that doesn’t work …

If I call the method directly via button in IB, then the UITextView changes his content successfully:

- (IBAction) clickButton
{
  fileContent.text = @"Test";
}

What could be the problem?

Thanks for your answers!

EDIT 2: I solved the problem by setting “filePath” after pushing the view:

- (IBAction) showFileContent {

FileContentsViewController *fileContentsViewController = [[FileContentsViewController alloc] init];
[self.navigationController pushViewController:fileContentsViewController animated:YES];
fileContentsViewController.filePath = self.filePath;
fileContentsViewController.title = [NSString stringWithFormat:@"Content from von %@", [filePath lastPathComponent]];
[fileContentsViewController release];

}

EDIT 1: Here’s the code of my interface:

@interface FileContentsViewController : UIViewController {

NSString *filePath;
UITextView *fileContent;

}

- (void) methodCall;

@property (nonatomic, retain) NSString *filePath;
@property (nonatomic, retain) IBOutlet UITextView *fileContent;

@end

… and here’s the code of the implementation:

#import "FileContentsViewController.h"


@implementation FileContentsViewController

@synthesize filePath;
@synthesize fileContent;

- (void) setFilePath:(NSString *) p
{
    NSLog(@"setFilePath executed!");
    [self methodCall];
} 

- (void) methodCall
{
    fileContent.text = @"Test"; // UITextView
}

// some standard methods

@end

… and finally the code of the method that sets “filePath”:

- (IBAction) showFileContent {

FileContentsViewController *fileContentsViewController = [[FileContentsViewController alloc] init];
fileContentsViewController.filePath = self.filePath;
fileContentsViewController.title = [NSString stringWithFormat:@"Content from von %@", [filePath lastPathComponent]];
[self.navigationController pushViewController:fileContentsViewController animated:YES];
[fileContentsViewController release];

}

Answer 1

What it looks like is that the fileContentsViewController created in -showFileContent doesn’t have anything assigned to its FileContentsViewController.fileContent (or, at least, fileContent doesn’t point to a UITextView that gets displayed) when fileContentsViewController.filePath is set.

You set filePath immediately after creating fileContentsViewController. If FileContentsViewController‘s -init doesn’t create an appropriate fileContent, then when -setFilePath: is called from -showFileContent, there’s no fileContent to set the text of. If fileContentsViewController is a typical view controller, fileContent won’t exist until fileContentsViewController is loaded, which (I believe) happens during -pushViewController:animated.

One fix is to override -setFileContent to set fileContent.text as appropriate:

-(void)setFileContent:(UITextView*)fileContentView {
    if (fileContent != fileContentView) {
        [fileContent release];
        fileContent = [fileContentView retain];
        if (self.filePath) { // if file path is not nil
            fileContent.text = ...;
        }
    }
}

Another other fix is to ensure you only set filePath when fileContent exists, but this is more brittle. A third is to set filePath after you push fileContentsViewController.

The way you would discover the cause during debugging is to check two things: execution (“Is the code I’m expecting to be executed ever reached?”) and data (“Do the variables hold the values I expect?”). Set breakpoints in -showFileContent and -methodCall so you know that the methods are being called (which would be one reason for failure). If execution makes it into -methodCall, the problem must be something else. From there, examine the values of the variables used in -methodCall and you’ll discover fileContent is either nil or not the same fileContent that shows up later.