Objective-C中的方法调用

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

Have you checked that fileContent has been set up at the time setFilePath is called? If you're trying to set things up at start up then it's possible that you're making calls before the views have been loaded (which the OS delays until the last possible moment).

You can force views to load by calling [self view] just before you try to access any of your Interface Builder views (NB don't call loadView - that doesn't do what you'd think).

Answer 2

If the problem is that setFilePath: is not called that I would guess that your code looks like

filePath = @"some value";

when it should be

self.filePath = @"some value";

When using @property you need to use self.filePath to call the methods, otherwise you will just access the ivar directly.

Answer 3

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.

Answer 4

How have you define filePath property ?
I think that it is the problem...