Read and Write NSArray, NSDictionary and NSSet to a File

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With just a few lines of code, you can read/write collections to/from files. The code below shows examples for writing and reading both NSArray and NSDictionary objects, the same logic would apply to an NSSet (or other collection type).

The example below starts by populating both an array and dictionary, each using the Objective-C literal syntax. Read more about using NSArray literals andNSDictionary literals.

Read and Write Collections to File

The process is straightforward:

– Create the NSArray and NSDictionary objects
– Obtain the path to write/read the files (application Documents directory)
– Append filenames to path for each collection type
– Use the ‘writeToFile:’ method of each object to save contents to file

NSString  *arrayPath;

NSString  *dictPath;

NSArray *array = @[@"IPA", @"Pilsner", @"Stout"];

 

NSDictionary *dictionary = @{@"key1" : array,

                             @"key2" : @"Hops",

                             @"key3" : @"Malt",

                             @"key4" : @"Yeast" };

 

// Get path to documents directory

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,

  NSUserDomainMask, YES);

 

if ([paths count] > 0)

{

  // Path to save array data

  arrayPath = [[paths objectAtIndex:0]

      stringByAppendingPathComponent:@"array.out"];

 

  // Path to save dictionary

  dictPath = [[paths objectAtIndex:0]

      stringByAppendingPathComponent:@"dict.out"];

 

  // Write array

  [array writeToFile:arrayPath atomically:YES];

 

  // Write dictionary

  [dictionary writeToFile:dictPath atomically:YES];

}

Read NSArray NSDictionary NSSet From File

The code to read back from the collections is equally as simple, using the methods arrayWithContentsOfFile: and dictionaryWithContentsOfFile: read from the file paths created previously to read the save data:

// Read both back into new NSArray and NSDictionary object

NSArray *arrayFromFile = [NSArray arrayWithContentsOfFile:arrayPath];

NSDictionary *dictFromFile = [NSDictionary dictionaryWithContentsOfFile:dictPath];

 

// Print the contents

for (NSString *element in arrayFromFile)

  NSLog(@"Beer: %@", element);

 

for (NSString *key in dictFromFile)

  NSLog(@"%@ : %@", key, [dictionary valueForKey:key]);

The output in the console window is below:

Beer: IPA

Beer: Pilsner

Beer: Stout

key1 : (

    IPA,

    Pilsner,

    Stout

)

key2 : Hops

key3 : Malt

key4 : Yeast

巴特西

Read and Write NSArray, NSDictionary and NSSet to a File

Read and Write Collections to File

Read NSArray NSDictionary NSSet From File

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