从 plist 读取数据的问题

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];


}

I have saved the value in the plist... now I want to retrieve it. If i print that by using NSLog it displays 0. How should I retrieve the value?

Answer 1

The Problem

In your code:

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

path contains a file path rooted at the document directory. Let's say it's …/plist.plist .

NSFileManager *fileManager = [NSFileManager defaultManager];

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

This is odd. If the file doesn't exist, you append /plist.plist to the path variable, which becomes …/plist.plist/plist.plist , which most likely doesn't exist. Considering this,

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

-initWithContentsOfFile: returns nil , so data is nil , so:

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

doesn't do anything and in:

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

savedStock is also nil , hence -objectForKey: followed by -intValue returns 0.

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

To validate my assumption, use the debugger or NSLog() to inspect the contents of path , data , and savedStock .

One Solution

If the file doesn't exist, you cannot read from it. Hence:

NSFileManager *fileManager = [NSFileManager defaultManager];

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

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

should be:

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];
}

and:

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

should create …/plist.plist containing the dictionary. And:

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

should work because the corresponding file was created in the previous steps.

Answer 2

contentArray = [NSArray arrayWithContentsOfFile:plistPath];

you need to place the above code where you want to get values from your plist file. You just need to give it your plist's path and it will convert your plist file into an array. Then you can access this array to get data from your plist file.