将项目附加到保存在 plist 中的 NSDictionary 中的现有键

Question

如何从 plist 将值附加到 NSDictionary 中的现有键？

我所拥有的基本上是一个保存在磁盘中的 plist，其中包含一些键和值，键是一些具有一个初始值的学生的姓名。我试图做的不起作用是通过读取 plist 将更多项目附加到现有键/学生，将其添加到临时 NSDictionary，将临时数组附加到 plist 中的现有键但是当我保存plist back 它不起作用，它只保存最后两项，并且基本上删除了该键的初始值。

这是我正在使用的代码……

- (IBAction)testing:(id)sender
{
    NSArray *dirPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsPath = [dirPaths objectAtIndex:0];
    NSString *fullPath = [documentsPath stringByAppendingPathComponent:@"studentsRecords.plist"];

    BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:fullPath];

    if(fileExists)
    {
        NSMutableDictionary *dictionaryRecords = [[NSMutableDictionary alloc]initWithContentsOfFile:fullPath];
        NSLog(@"Items for Nathan: %@",[dictionaryRecords objectForKey:@"Nathan"]);// here the output is, Items for Nathan: Ruler
        // which make sense since I only had one initial record for Nathan in my plist,

        // Here, I want to add two more items to the key Nathan by appending an arry to
        // NSMutableDictionary (dictionaryRecords) but it doesnt work
        NSArray *tempArray = @[@"NoteBook", @"Pencil"];
        [dictionaryRecords setObject:tempArray forKey:@"Nathan"];

        [dictionaryRecords writeToFile:fullPath atomically:YES];
        // when I check the plist after saving this, I only see the last two values, NoteBook and Pencil
        // instead of the three that I'm expecting, Ruler, NoteBook and Pencil
    }

}

我在这里缺少什么？

非常感谢。

Answer 1

[dictionaryRecords setObject:tempArray forKey:@"Nathan"] 用tempArray 替换之前的值。

如果要添加到现有数组，则必须检索它，制作可变副本，然后附加到它。

Answer 2

这是我如何使它工作的。我希望我在这里没有把事情搞得太复杂，但由于某种原因，我不得不使用两个数组，一个 NSArray 和一个 NSMutableArray，我认为 NSMutableArray 就足够了，但它不起作用。

- (IBAction)testing:(id)sender
{
    // get directory path
    NSArray *dirPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsPath = [dirPaths objectAtIndex:0];
    // create plist
    NSString *fullPath = [documentsPath stringByAppendingPathComponent:@"studentsRecords.plist"];

    BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:fullPath];

    // if file exists create dictionary
    if(fileExists)
    {
        // add items from plist to dictionary
        NSDictionary *dictionaryExistingRecords = [[NSDictionary alloc]initWithContentsOfFile:fullPath];
        // make a copy if dictinary with existing items
        NSMutableDictionary *dictionaryNewRecords = [dictionaryExistingRecords mutableCopy];
        // array to hold existing values from a spcecified key
        NSArray *arrayWithExistingKey = [dictionaryExistingRecords objectForKey:@"Nathan"];
        // mutable array to add existing and be able to insert new items
        NSMutableArray *arrayOldAndNewItems = [NSMutableArray arrayWithArray:arrayWithExistingKey];
        // insert new items to array
        [arrayOldAndNewItems addObject:@"Snow Pans"];
        // add old and new items to specified key
        [dictionaryNewRecords setObject:arrayOldAndNewItems forKey:@"Nathan"];
        // save new records to plist
        [dictionaryNewRecords writeToFile:fullPath atomically:YES];
    }
}
@end