Question

我是iphone开发的新手。我正在做一个基于导航的应用程序，我无法将值传递给新视图。

@interface RootViewController : UITableViewController {
    NSString *imgurl;
    NSMutableArray *galleryArray;
}

@property (nonatomic, retain) NSString *imgurl;
@property (nonatomic, retain) NSMutableArray *galleryArray;

- (void)showAll;

@end

#import "RootViewController.h"
#import "ScrollView.h"
#import "Model.h"
#import "JSON/JSON.h"

@implementation RootViewController

@synthesize galleryArray, imgurl;

- (void)viewDidLoad {   
    UIBarButtonItem *showButton = [[[UIBarButtonItem alloc]
                                initWithTitle:NSLocalizedString(@"Show All", @"")
                                style:UIBarButtonItemStyleBordered
                                target:self
                                action:@selector(showAll)] autorelease];
    self.navigationItem.rightBarButtonItem = showButton;

    NSString *jsonString = [[Model sharedInstance] jsonFromURLString:@"http://www.ddbstaging.com/gerald/gallery.php"];
    NSDictionary *resultDictionary = [jsonString JSONValue];

    if (resultDictionary == nil) {
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Webservice Down" 
                                                    message:@"The webservice you are accessing is currently down. Please try again later." 
                                                   delegate:self 
                                          cancelButtonTitle:@"OK" 
                                          otherButtonTitles:nil];
        [alert show];
        [alert release];
    }
    else {
        galleryArray = [[NSMutableArray alloc] init];
        galleryArray = [resultDictionary valueForKey:@"gallery"];
        imgurl = (NSString *)[galleryArray objectAtIndex:0];
        NSLog(@" -> %@", galleryArray);
        NSLog(imgurl);
    }
}

- (void)showAll {
    NSLog(@" -> %@", galleryArray);
    NSLog(imgurl);
    ScrollView *controller = [[ScrollView alloc] initWithJSON:galleryArray];
    [self.navigationController pushViewController:controller animated:YES];
}

RootViewController启动和json数据加载正常。我可以从第一个控制台跟踪中看到它。但是，一旦我单击“全部显示”按钮，应用程序就会崩溃。它甚至没有跟踪galleryArray和imgurl。

也许额外的一双眼睛可以发现我的错误。非常感谢任何帮助！

[Session started at 2010-05-08 16:16:07 +0800.]
2010-05-08 16:16:07.242 Photos[5892:20b]  -> (
)
GNU gdb 6.3.50-20050815 (Apple version gdb-967) (Tue Jul 14 02:11:58 UTC 2009)
Copyright 2004 Free Software Foundation, Inc.
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Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i386-apple-darwin".sharedlibrary apply-load-rules all
Attaching to process 5892.
(gdb)

Answer 1

（1）尝试使用

NSLog(@"%@", imgurl);

NSLog的第一个参数始终被解释为格式字符串，即使它是一个变量（运行时也不关心）。如果imgurl包含格式说明符（例如%2c），则可能会发生未定义的内容。

（2）

    galleryArray = [[NSMutableArray alloc] init];
    galleryArray = [resultDictionary valueForKey:@"gallery"];
    imgurl = (NSString *)[galleryArray objectAtIndex:0];
    NSLog(@" -> %@", galleryArray);
    NSLog(imgurl);

这里有两个问题。第二行将覆盖在第一行中初始化的空可变数组，从而导致内存泄漏。在第二行中分配的galleryArray可能会在函数结束后释放，从而创建一个悬空指针。 imgurl也是如此。这可能是崩溃的主要原因。我建议你再次阅读Cocoa Memory Management Rules。无论如何，这段代码应该是：

    self.galleryArray = [resultDictionary valueForKey:@"gallery"];
    self.imgurl = [galleryArray objectAtIndex:0];
    NSLog(@" -> %@", galleryArray);
    NSLog(@"%@", imgurl);

或

    [galleryArray release];
    galleryArray = [[resultDictionary valueForKey:@"gallery"] retain];
    [imgurl release];
    imgurl = [[galleryArray objectAtIndex:0] retain]; // or -copy.
    NSLog(@" -> %@", galleryArray);
    NSLog(@"%@", imgurl);

Objective-C：未保存或传递的属性

1 个答案: