將項目附加到保存在plist中的NSDictionary中的現有密鑰

Question

如何將值附加到來自plist的NSDictionary中的現有密鑰？

我所擁有的基本上是保存在具有幾個鍵和值的光盤中的plist，這些鍵是具有一個初始值的一些學生的名字。我試圖做的是不工作的是通過閱讀plist將更多項添加到現有的鍵/學生，將其添加到臨時NSDictionary，將臨時數組添加到plist中的現有鍵，但是當我保存plist返回它不起作用，它只保存最後兩項，並基本刪除該項的初始值。

這裏是我正在使用的代碼...

- (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 
    } 

} 

缺少什麼我在這裏？

非常感謝。

Answer 1

[dictionaryRecords setObject:tempArray forKey:@"Nathan"]取代以前的值是tempArray。

如果你想添加到現有的數組，你必須檢索它，做一個可變的副本，並追加到它。

Answer 2

這是我如何使它工作。我希望我沒有在這裏複雜的東西，但由於某種原因，我不得不使用兩個數組，一個NSArray和一個NSMutableArray，我會認爲NSMutableArray就足夠了，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