奇怪的 plist 行为在第一个值上返回 null ，当它应该是 12 时返回 13 个结果答案

【问题标题】：Weird plist behaviour returning null on first value and 13 results when it should be 12奇怪的 plist 行为在第一个值上返回 null ，当它应该是 12 时返回 13 个结果
【发布时间】：2013-05-21 20:56:23
【问题描述】：

在使用 plist 并尝试返回数据时，我遇到了这种奇怪的行为。为了给你一个概述，plist 在每个对象中有 12 个条目，所以我希望有 12 个，但我得到了 13 个，第一个结果是 null 而其余的 12 个实际上是正确的。

这是我的 plist 文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Name</key>
    <array>
        <string>Audit</string>
        <string>Tax</string>
        <string>Digital</string>
        <string>Consulting</string>
        <string>Risk Advisory</string>
        <string>Finance</string>
        <string>Audit</string>
        <string>Tax</string>
        <string>Digital</string>
        <string>Consulting</string>
        <string>Advisory</string>
        <string>Finance</string>
    </array>
    <key>Logo</key>
    <array>
        <string>page.png</string>
        <string>page.png</string>
        <string>page.png</string>
        <string>page.png</string>
        <string>page.png</string>
        <string>page.png</string>
        <string>page.png</string>
        <string>page.png</string>
        <string>page.png</string>
        <string>page.png</string>
        <string>page.png</string>
        <string>page.png</string>
    </array>
</dict>
</plist>

这是我的 ViewController.h 文件：

#import <UIKit/UIKit.h>
#import "iCarousel.h"


@interface PackViewController : UIViewController <iCarouselDataSource, iCarouselDelegate>
{
    NSMutableArray      *packName;
    NSMutableArray      *packLogo;
}

@property (nonatomic, retain) IBOutlet iCarousel *carousel;
@property (nonatomic, retain) NSMutableArray  *packName;
@property (nonatomic, retain) NSMutableArray  *packLogo;

@end

然后，这是我的 ViewController.m 文件：

#import "PackViewController.h"
#import "AsyncImageView.h"


@interface PackViewController () <UIActionSheetDelegate>

@property (nonatomic, assign) BOOL wrap;
@property (nonatomic, retain) NSMutableArray *items;

@end


@implementation PackViewController

@synthesize carousel, wrap, items;
@synthesize packName, packLogo;

- (void)awakeFromNib
{
    //set up data
    wrap = YES;

    NSString *plistPath = [[NSBundle mainBundle] pathForResource:@"Pack" ofType:@"plist"];
    NSArray *plistItems = [NSDictionary dictionaryWithContentsOfFile:plistPath];
    NSArray *plistData = [plistItems valueForKey:@"Name"];

    self.items = [NSMutableArray array];
    for (int i = 0; i < [plistData count]; i++)
    {
        [items addObject:[NSNumber numberWithInt:i]];
        NSLog(@"First Index Name %@",[items objectAtIndex:i]);
    }
}

- (void)dealloc
{
    carousel.delegate = nil;
    carousel.dataSource = nil;

    [carousel release];
    [super dealloc];
}

#pragma mark -
#pragma mark View lifecycle

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Pack.plist code
    // get paths from root direcory
    NSArray *paths = NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES);
    // get documents path
    NSString *documentsPath = [paths objectAtIndex:0];
    // get the path to our Pack.plist file
    NSString *plistPath = [documentsPath stringByAppendingPathComponent:@"Pack.plist"];

    // check to see if Pack.plist exists in documents
    if (![[NSFileManager defaultManager] fileExistsAtPath:plistPath])
    {
        // if not in documents, get property list from main bundle
        plistPath = [[NSBundle mainBundle] pathForResource:@"Pack" ofType:@"plist"];
    }

    // read property list into memory as an NSData object
    NSData *plistXML = [[NSFileManager defaultManager] contentsAtPath:plistPath];
    NSString *errorDesc = nil;
    NSPropertyListFormat format;
    // convert static property list into dictionary object
    NSDictionary *temp = (NSDictionary *)[NSPropertyListSerialization
                                          propertyListFromData:plistXML
                                          mutabilityOption:NSPropertyListMutableContainersAndLeaves
                                          format:&format
                                          errorDescription:&errorDesc];
    if (!temp)
    {
        NSLog(@"Error reading plist: %@, format: %d", errorDesc, format);
    }
    // assign values
    self.packName = [NSMutableArray arrayWithArray:[temp objectForKey:@"Name"]];
    self.packLogo = [NSMutableArray arrayWithArray:[temp objectForKey:@"Logo"]];

    // configure carousel
    carousel.type = iCarouselTypeInvertedWheel;
    carousel.vertical = true;
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    self.carousel = nil;
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return YES;
}

#pragma mark -
#pragma mark UIActionSheet methods

- (void)actionSheet:(UIActionSheet *)actionSheet didDismissWithButtonIndex:(NSInteger)buttonIndex
{
    if (buttonIndex >= 0)
    {
        //map button index to carousel type
        iCarouselType type = buttonIndex;

        //carousel can smoothly animate between types
        [UIView beginAnimations:nil context:nil];
        carousel.type = type;
        [UIView commitAnimations];
    }
}

#pragma mark -
#pragma mark iCarousel methods

- (NSUInteger)numberOfItemsInCarousel:(iCarousel *)carousel
{
    //NSLog(@"numberOfItemsInCarousel count: %i", [items count]);
    return [items count];
}

- (UIView *)carousel:(iCarousel *)carousel viewForItemAtIndex:(NSUInteger)index reusingView:(UIView *)view
{
    UIButton *button = (UIButton *)view;
    UILabel *label = nil;

    if (button == nil)
    {
        //no button available to recycle, so create new one
        UIImage *image = [UIImage imageNamed:[NSString stringWithFormat:@"%@", [packLogo objectAtIndex:index]]];
        //NSLog(@"companyLogo: %@", [packLogo objectAtIndex:index]);
        button = [UIButton buttonWithType:UIButtonTypeCustom];
        button.frame = CGRectMake(0.0f, 0.0f, image.size.width, image.size.height);
        [button setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
        [button setBackgroundImage:image forState:UIControlStateNormal];
        button.titleLabel.font = [button.titleLabel.font fontWithSize:20];
        [button addTarget:self action:@selector(buttonTapped:) forControlEvents:UIControlEventTouchUpInside];

        label = [[[UILabel alloc] initWithFrame:view.bounds] autorelease];
        label.backgroundColor = [UIColor clearColor];
        label.textAlignment = UITextAlignmentCenter;
    }
    else
    {
        //get a reference to the label in the recycled view
        label = (UILabel *)[view viewWithTag:1];
    }
    //set button label
    [button setTitle:[self.packName objectAtIndex:index] forState:UIControlStateNormal];
    NSLog(@"companyName: %@", [items objectAtIndex:index]);

    return button;
}

#pragma mark -
#pragma mark item tap event

- (void)buttonTapped:(UIButton *)sender
{
    //get item index for button
    NSInteger index = [carousel indexOfItemViewOrSubview:sender];

    [[[[UIAlertView alloc] initWithTitle:@"Button Tapped"
                                 message:[NSString stringWithFormat:@"You tapped button number %i", index]
                                delegate:nil
                       cancelButtonTitle:@"OK"
                       otherButtonTitles:nil] autorelease] show];
}

- (CATransform3D)carousel:(iCarousel *)_carousel itemTransformForOffset:(CGFloat)offset baseTransform:(CATransform3D)transform
{
    CGFloat count = _carousel.numberOfVisibleItems;
    CGFloat spacing = 1.0f;
    CGFloat arc = M_PI * 2.0f;
    CGFloat radius = _carousel.itemWidth * spacing * count / arc;
    CGFloat angle = arc / count * offset;

    return CATransform3DTranslate(transform, radius - radius * cos(angle), radius * sin(angle), 0.0f);
}

- (CGFloat)carousel:(iCarousel *)_carousel valueForOption:(iCarouselOption)option withDefault:(CGFloat)value
{
    //customise carousel display
    switch (option)
    {
        case iCarouselOptionWrap:
        {
            //normally you would hard-code this to YES or NO
            return wrap;
        }
        case iCarouselOptionSpacing:
        {
            //add a bit of spacing between the item views
            return value * 1.05f;
        }
        case iCarouselOptionFadeMax:
        {
            if (carousel.type == iCarouselTypeCustom)
            {
                //set opacity based on distance from camera
                return 0.0f;
            }
            return value;
        }
        default:
        {
            return value;
        }
    }
}

@end

您可以看到我的 M 文件中有两行代码输出两个 NSLog 项。它们是：

NSLog(@"First Index Name %@",[items objectAtIndex:i]);
NSLog(@"companyName: %@", [items objectAtIndex:index]);

awakeFromNib 中 for 循环中包含的“第一个索引名称”的输出是：

2013-05-21 22:43:23.875 Pack[7496:c07] First Index Name 0
2013-05-21 22:43:23.877 Pack[7496:c07] First Index Name 1
2013-05-21 22:43:23.878 Pack[7496:c07] First Index Name 2
2013-05-21 22:43:23.879 Pack[7496:c07] First Index Name 3
2013-05-21 22:43:23.880 Pack[7496:c07] First Index Name 4
2013-05-21 22:43:23.880 Pack[7496:c07] First Index Name 5
2013-05-21 22:43:23.881 Pack[7496:c07] First Index Name 6
2013-05-21 22:43:23.881 Pack[7496:c07] First Index Name 7
2013-05-21 22:43:23.882 Pack[7496:c07] First Index Name 8
2013-05-21 22:43:23.882 Pack[7496:c07] First Index Name 9
2013-05-21 22:43:23.883 Pack[7496:c07] First Index Name 10
2013-05-21 22:43:23.883 Pack[7496:c07] First Index Name 11

如您所见，我以正确的顺序获得了所有 12 个值，这是我对第二个值的期望，但这就是问题所在。对于包含在 -(UIView *)carousel:(iCarousel *)carousel viewForItemAtIndex:(NSUInteger)index reusingView:(UIView *)view 中的第二个 NSLog我输出items 数组只是为了看看发生了什么。这是我看到的：

2013-05-21 22:43:23.916 Pack[7496:c07] companyName: 0
2013-05-21 22:43:23.918 Pack[7496:c07] companyName: 0
2013-05-21 22:43:23.919 Pack[7496:c07] companyName: 11
2013-05-21 22:43:23.920 Pack[7496:c07] companyName: 7
2013-05-21 22:43:23.921 Pack[7496:c07] companyName: 6
2013-05-21 22:43:23.922 Pack[7496:c07] companyName: 2
2013-05-21 22:43:23.922 Pack[7496:c07] companyName: 1
2013-05-21 22:43:23.923 Pack[7496:c07] companyName: 10
2013-05-21 22:43:23.924 Pack[7496:c07] companyName: 9
2013-05-21 22:43:23.925 Pack[7496:c07] companyName: 8
2013-05-21 22:43:23.925 Pack[7496:c07] companyName: 5
2013-05-21 22:43:23.926 Pack[7496:c07] companyName: 4
2013-05-21 22:43:23.927 Pack[7496:c07] companyName: 3

同样，前两个结果都是0，与第一次迭代不同，排序非常混乱。我found a thread on SO 提到 plist 不一定按顺序输出，因为它们只是关键对象，所以我明白了，但核心问题是前两个结果。

如果我将我的 NSLog 更改为输出 self.packName 的结果（如下所示：NSLog(@"companyName: %@", [self.packName objectAtIndex:index]);），返回的内容如下：

2013-05-21 22:49:43.663 Pack[7543:c07] companyName: (null)
2013-05-21 22:49:43.665 Pack[7543:c07] companyName: Audit
2013-05-21 22:49:43.666 Pack[7543:c07] companyName: Finance
2013-05-21 22:49:43.667 Pack[7543:c07] companyName: Tax
2013-05-21 22:49:43.668 Pack[7543:c07] companyName: Audit
2013-05-21 22:49:43.669 Pack[7543:c07] companyName: Digital
2013-05-21 22:49:43.669 Pack[7543:c07] companyName: Tax
2013-05-21 22:49:43.670 Pack[7543:c07] companyName: Risk Advisory
2013-05-21 22:49:43.671 Pack[7543:c07] companyName: Consulting
2013-05-21 22:49:43.672 Pack[7543:c07] companyName: Digital
2013-05-21 22:49:43.672 Pack[7543:c07] companyName: Finance
2013-05-21 22:49:43.673 Pack[7543:c07] companyName: Risk Advisory
2013-05-21 22:49:43.673 Pack[7543:c07] companyName: Consulting

正如您再次看到的那样，第一个结果是 (null)，我很难理解为什么会这样。

为了进一步调试，我运行了这个 NSLog：NSLog(@"companyName: %@", packName); 以将原始结果输出为数组，这些是结果：

2013-05-21 22:52:59.284 Pack[7581:c07] companyName: (
    "Audit",
    "Tax",
    "Digital",
    "Consulting",
    "Risk Advisory",
    "Finance",
    "Audit",
    "Tax",
    "Digital",
    "Consulting",
    "Advisory",
    "Finance"
)

数组中没有(null) 结果，所以我不知道这个流氓空值是从哪里来的。

任何帮助将不胜感激！！！！

【问题讨论】：

标签： ios objective-c plist icarousel

【解决方案1】：

对于包含在 carousel:viewForItemAtIndex:reusingView: 中的第二个 NSLog，我输出 items 数组只是为了看看发生了什么。

不，您输出的正是items 的一个元素：具有在 iCarousel 委托回调中传递的索引的那个。您无法控制 iCarousel 何时发送此消息并且未指定索引的顺序。这解释了以下输出

2013-05-21 22:43:23.916 Pack[7496:c07] companyName: 0
2013-05-21 22:43:23.918 Pack[7496:c07] companyName: 0
2013-05-21 22:43:23.919 Pack[7496:c07] companyName: 11
...

同样，前两个结果都是 0，并且与第一次迭代不同，排序非常混乱。我在 SO 上发现了一个线程，其中提到 plist 不一定按顺序输出，因为它们只是关键对象，所以我明白了，但核心问题是前两个结果。

如上所述，顺序取决于 iCarousel 实现。它与 plist 无关。您误读了链接的帖子，它可能与字典中的顺序有关。当然，plist 会保留数组元素的顺序。

如果我更改我的 NSLog 以输出 self.packName 的结果（如下所示：NSLog(@"companyName: %@", [self.packName objectAtIndex:index]);) 这是返回的内容：

2013-05-21 22:49:43.663 Pack[7543:c07] companyName: (null)
2013-05-21 22:49:43.665 Pack[7543:c07] companyName: Audit
...

带有 (null) 结果的行只能表示一件事：在第一次回调时，items ivar 尚未初始化。 objectAtIndex: 永远无法返回 nil，所以这是唯一的解释。您可以使用调试器检查，在回调中设置断点和awakeFromNib。

【讨论】：

感谢@Nikolai Ruhe 让我朝着正确的方向前进。如果您查看我上面的代码，您会发现在viewDidLoad 和awakeFromNib 中我两次拉入plist。解决方法是巩固这一点并将 plist 代码放在 awakeFromNib 中，然后将其从 viewDidLoad 中删除。