嘗試在Xcode中存檔自定義對象時出錯

我試圖使用NSCoder將自定義對象（我的對象是一個庫，如在檢查出圖書的地方）存檔到iPhone的文件系統。但是，當我嘗試撥打NSKeyedArchiver archiveRootObject時，出現「發送到實例的無法識別的選擇器」錯誤。該庫聲明NSCoding協議並實現所需的方法。我很茫然。嘗試在Xcode中存檔自定義對象時出錯

對象接口（library.h）：

#import <Foundation/Foundation.h> 
@interface Library : NSObject <NSCoding> { 
int numCopies; 
NSString *location; 
NSString *locationInfo; 
NSString *material; 
NSString *library; 
} 
+ (id)library; 
@property (nonatomic) int numCopies; 
@property (retain) NSString *location; 
@property (retain) NSString *locationInfo; 
@property (retain) NSString *material; 
@property (retain) NSString *library; 
- (void)encodeWithCoder:(NSCoder *)encoder; 
- (void)initWithCoder:(NSCoder *)decoder; 
@end

對象實現的相關部分（library.m）：

#import "library.h" 

@implementation Library 

@synthesize numCopies; 
@synthesize location; 
@synthesize locationInfo; 
@synthesize material; 
@synthesize library; 

+ (id)library 
{ 
return [[Library alloc] init]; 
} 

-(void)encodeWithCoder:(NSCoder *)encoder 
{ 
    //for each instance variable, archive it under its variable name 
    [encoder encodeObject:numCopies forkey:@"numCopies"]; 
    [encoder encodeObject:location forkey:@"location"]; 
    [encoder encodeObject:locationInfo forkey:@"locationInfo"]; 
    [encoder encodeObject:material forkey:@"material"]; 
    [encoder encodeObject:library forkey:@"library"]; 
}

最後，的viewController（libTableViewController.m）

//try to archive the library object 
NSString *savePath = pathInDocumentDirectory(@"lib.data"); 
NSLog(@"try to archive library to path: %@", savePath); 
[NSKeyedArchiver archiveRootObject:this_lib toFile:savePath];

這是錯誤：

2011-12-18 12:13:38.799 LibraryFiend2[12877:207] try to archive library to path: /Users/kclary/Library/Application Support/iPhone Simulator/4.3/Applications/71B11434-3307-449A-9E95-5E22034E7FA0/Documents/lib.data 
2011-12-18 12:13:38.800 LibraryFiend2[12877:207] -[NSKeyedArchiver encodeObject:forkey:]: unrecognized selector sent to instance 0x4b1a130 
2011-12-18 12:13:38.801 LibraryFiend2[12877:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSKeyedArchiver encodeObject:forkey:]: unrecognized selector sent to instance 0x4b1a130' 
terminate called after throwing an instance of 'NSException'

如果我將一個簡單的數組替換爲我的庫對象，它就可以工作。

來源

2011-12-21 Kevin Clary