从 plist 读取数据时出现问题

Question

- (void)viewDidLoad {
   [super viewDidLoad];

    paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
    NSString *documentsDirectory = [paths objectAtIndex:0]; 
    path = [documentsDirectory stringByAppendingPathComponent:@"plist.plist"]; 

    NSFileManager *fileManager = [NSFileManager defaultManager];

    if (![fileManager fileExistsAtPath: path]) 
    {
        path = [documentsDirectory stringByAppendingPathComponent: [NSString stringWithFormat: @"plist.plist"] ];
    }

    NSMutableDictionary *data = [[NSMutableDictionary alloc] initWithContentsOfFile: path];
    int value = 5;
    [data setObject:[NSNumber numberWithInt:value] forKey:@"value"];
    [data writeToFile: path atomically:YES];
    [data release];

    NSMutableDictionary *savedStock = [[NSMutableDictionary alloc] initWithContentsOfFile: path];
    int value1;
    value1 = [[savedStock objectForKey:@"value"] intValue];
    **NSLog(@"%i",value1);**
    [savedStock release];


}

我已将值保存在 plist 中...现在我想检索它。如果我使用 NSLog 打印它，它会显示 0。我应该如何检索该值？

Answer 1

问题

在您的代码中：

paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
NSString *documentsDirectory = [paths objectAtIndex:0]; 
path = [documentsDirectory stringByAppendingPathComponent:@"plist.plist"]; 

path 包含以文档目录为根的文件路径。假设它是 …/plist.plist。

NSFileManager *fileManager = [NSFileManager defaultManager];

if (![fileManager fileExistsAtPath: path]) 
{
    path = [documentsDirectory stringByAppendingPathComponent: [NSString stringWithFormat: @"plist.plist"] ];
}

这很奇怪。如果该文件不存在，请将 /plist.plist 附加到 path 变量，该变量将变为 .../plist.plist/plist.plist，这很可能不存在。考虑到这一点，

NSMutableDictionary *data = [[NSMutableDictionary alloc] initWithContentsOfFile: path];

-initWithContentsOfFile:返回nil，因此data是nil，所以：

int value = 5;
[data setObject:[NSNumber numberWithInt:value] forKey:@"value"];
[data writeToFile: path atomically:YES];
[data release];

不执行任何操作并且in:

NSMutableDictionary *savedStock = [[NSMutableDictionary alloc] initWithContentsOfFile: path];
int value1;
value1 = [[savedStock objectForKey:@"value"] intValue];

savedStock 也是 nil，因此 -objectForKey: 后跟 -intValue 返回 0。

NSLog(@"%i",value1);
[savedStock release];

验证我的假设，使用调试器或NSLog() 用于检查 path、data 和 savedStock 的内容。

一种解决方案

如果该文件不存在，则无法读取该文件。因此：

NSFileManager *fileManager = [NSFileManager defaultManager];

if (![fileManager fileExistsAtPath: path]) 
{
    path = [documentsDirectory stringByAppendingPathComponent: [NSString stringWithFormat: @"plist.plist"] ];
}

NSMutableDictionary *data = [[NSMutableDictionary alloc] initWithContentsOfFile: path];

应该是：

NSFileManager *fileManager = [NSFileManager defaultManager];
NSMutableDictionary *data;

if ([fileManager fileExistsAtPath: path]) 
{
    // If the file exists, read dictionary from file
    data = [[NSMutableDictionary alloc] initWithContentsOfFile: path];
}
else
{
    // If the file doesn’t exist, create an empty dictionary
    data = [[NSMutableDictionary alloc] init];
}

并且：

int value = 5;
[data setObject:[NSNumber numberWithInt:value] forKey:@"value"];
[data writeToFile: path atomically:YES];
[data release];

应该创建包含字典的 …/plist.plist 。并且：

NSMutableDictionary *savedStock = [[NSMutableDictionary alloc] initWithContentsOfFile: path];
int value1;
value1 = [[savedStock objectForKey:@"value"] intValue];
NSLog(@"%i",value1);
[savedStock release];

应该可以工作，因为在前面的步骤中创建了相应的文件。

Answer 2

contentArray = [NSArray arrayWithContentsOfFile:plistPath];

您需要将上述代码放在要从 plist 文件中获取值的位置。您只需要给它您的 plist 路径，它就会将您的 plist 文件转换为数组。然后您可以访问该数组以从 plist 文件中获取数据。