如何使用NSCoder

Question

我正在开发iphone应用程序。

我使用NSCoder。

MyApplication.h

#define ITEMS_KEY @"items"
#define CATEGORIES_KEY @"categories"


#import <UIKit/UIKit.h>


@interface MyApplicationData : NSObject <NSCoding, NSCopying> {
    NSMutableArray* items;
    NSMutableArray* categories;
}

@property (nonatomic ,retain) NSMutableArray* items;
@property (nonatomic, retain) NSMutableArray* categories;


@end

Myapplication.m

#import "MyApplicationData.h"


@implementation MyApplicationData

@synthesize items;
@synthesize categories;

#pragma mark NSCoding
- (void)encodeWithCoder:(NSCoder *)aCoder{
  [aCoder encodeObject:items forKey:ITEMS_KEY];
  [aCoder encodeObject:categories forKey:CATEGORIES_KEY];
}

-(id)initWithCoder:(NSCoder *)aDecoder{
  if(self = [super init]){
    self.items = [aDecoder decodeObjectForKey:ITEMS_KEY];
    self.categories = [aDecoder decodeObjectForKey:CATEGORIES_KEY];
  }
  return self;
}

#pragma mark -
#pragma mark NSCopying
-(id)copyWithZone:(NSZone *)zone{
  MyApplicationData* copy = [[[self class]allocWithZone:zone]init];
  items = [self.items copy];
  categories = [self.categories copy];
  return copy;
}

@end

但是警告。

'NSCoder' may not respond to '-decodeDataObjectForKey'

如何使用NSCoder？

Answer 1

使用-decodeObjectForKey:和read the documentation。

Answer 2

这是来自我的LogEntry对象的NSCoding协议方法，你可以忽略switch语句和模式细节，这些都来自我写的一个基类，它允许我保持对数据格式变化的正常跟踪。

请注意，除了使用decodeObjectForKey:您还需要确保保留/复制给定值，因为它们在收到时会自动释放。

- (id)initWithCoder:(NSCoder *)coder {
    self = [super initWithCoder:coder];

    if (self != nil) {
        switch ([schemaVersion intValue]) {
            case 2:
                filepath = [[coder decodeObjectForKey:@"filepath"] copy];
                identifier = [coder decodeInt64ForKey:@"identifier"];
                level = [coder decodeIntForKey:@"level"];
                lineNumber = [[coder decodeObjectForKey:@"lineNumber"] retain];
                message = [[coder decodeObjectForKey:@"message"] retain];
                timestamp = [[coder decodeObjectForKey:@"timestamp"] retain];
                break;              
            default:
                [self release], self = nil;
                break;
        }
    }

    return self;
}

- (void)encodeWithCoder:(NSCoder *)coder {
    [coder encodeObject:filepath forKey:@"filepath"];
    [coder encodeInt64:identifier forKey:@"identifier"];
    [coder encodeInt:level forKey:@"level"];
    [coder encodeObject:lineNumber forKey:@"lineNumber"];
    [coder encodeObject:message forKey:@"message"];
    [coder encodeObject:timestamp forKey:@"timestamp"];

    [super encodeWithCoder:coder];
}

Answer 3

我认为你应该使用-decodeObjectForKey: