Saving Array to Plist file that contains Custom Objects iPhone

Question

I have a class called XYZ inheriting from NSObject and an array which contains objects of XYZ. I need to write this array to a plist file on to documents directory. After trying

Answer 1

Conforming your XYZ class to the NSCoding protocol is indeed very suitable for what you're trying to do. To do so, add the NSCoding protocol to your class's interface declaration:

@interface XYZ <NSCoding>

Then, you need implement encodeWithCoder: and initWithCoder: in your implementation. "Encode with coder" means "take your object's current state, and pack it into a generic object called an 'encoder'". "Init with coder" means "given an already-packed encoder object, configure yourself with the data packed into the encoder". In both of these methods, the 'encoder' will be an instance of NSCoder, which has a fairly simple interface for encoding ("packing") and decoding ("unpacking") basic types.

Here's a sample implementation:

@implementation XYZ
- (id)initWithCoder:(NSCoder*)encoder
{
    self = [self init];

    if (self)
    {
        self.myIntProperty = [encoder decodeIntForKey:@"myInt"];
    }

    return self;
}

– (void)encodeWithCoder:(NSCoder*)decoder
{
    [decoder encodeInt:self.myIntProperty forKey:@"myInt"];
}

@end

Answer 2

There is a very good tutorial on the Ray Wenderlich's blog which explains how to work with the NSCoding.

Simply you just have to implement the *-(void)encodeWithCoder:(NSCoder )encode and *-(id)initWithCoder:(NSCoder )decoder methods in your object that respects the NSCoding protocol like that:

// Header
@interface AnObject: NSObject <NSCoding>

// Implementation
- (void) encodeWithCoder:(NSCoder *)encoder {
    [encoder encodeObject:ivar1 forKey:@"ivar1"];
    [encoder encodeFloat:ivar2 forKey:@"ivar2"];
}

- (id)initWithCoder:(NSCoder *)decoder {
    self = [super initWithCoder:coder];
    ivar1 = [[coder decodeObjectForKey:@"ivar1"] retain];
    ivar2 = [[coder decodeObjectForKey:@"ivar2"] retain];
    return self;
}

You can also check the official documentation here.

Answer 3

You need to implement two methods: -initWithCoder: and -encodeWithCoder:. Read the NSCoding docs; they’re pretty straight-forward methods. You basically want to encode/decode your instance variables with a key that corresponds to its name.

Answer 4

After implementing encodeWithCoder: and initWithCoder: for the custom class here is how to write and read:

Write:

NSError  *error;
NSData* archiveData = [NSKeyedArchiver archivedDataWithRootObject:yourClassInstance];
[archiveData writeToFile:filePath options:NSDataWritingAtomic error:&error];

Read:

NSData *archiveData = [NSData dataWithContentsOfFile:filePath];
YourClass *yourClassInstance = (NSArray*)[NSKeyedUnarchiver unarchiveObjectWithData:archiveData];

Answer 5

It's pretty straight forward. For given class Foo:

#import <Foundation/Foundation.h>

@interface Foo : NSObject <NSCoding> {
    NSArray* bar_;
    NSUInteger baz_;
}

@property (nonatomic, retain) NSArray *bar;
@property (nonatomic, assign) NSUInteger baz;

@end

All you have to do to conform to the NSCoding protocol is to implement the initWithCoder: and decodeWithCoder messages:

#import "Foo.h"

@implementation Foo
@synthesize bar = bar_;
@synthesize baz = baz_;

#pragma mark - NSCoding

- (void)encodeWithCoder:(NSCoder *)encoder  {
    [encoder encodeObject:self.bar forKey:@"bar"];
    [encoder encodeInteger:self.baz forKey:@"baz"];
}

- (id)initWithCoder:(NSCoder *)decoder  {
    if ((self = [super init])) {
        self.bar = [decoder decodeObjectForKey:@"bar"];
        self.baz = [decoder decodeIntegerForKey:@"baz"];
    }
    return self;
}

- (void) dealloc {

    [bar_ release];
    [super dealloc];    
}

@end