通过MFMailComposeController传输后，NSKeyedUnarchiver会产生nil值

Question

我正在使用MFMailComposeController发送密钥存档作为电子邮件的附件。我的应用程序读取电子邮件附件获取密钥存档，但取消归档它给出了nil值。详情如下：

发送视图控制器：

    - (IBAction)saveAndSend:(id)sender {

    // Email Subject
    NSString *emailTitle = @"Test Email";
    // Email Content
    NSString *messageBody = @"TimeChime Trace Data";
    // To address
    NSArray *toRecipents = [NSArray arrayWithObject:@"[email protected]"];

    if (![MFMailComposeViewController canSendMail]) {
        NSLog(@"Mail services are not available.");
        return;
    }
    MFMailComposeViewController *mc = [[MFMailComposeViewController alloc] init];
    mc.mailComposeDelegate = self;
    [mc setSubject:emailTitle];
    [mc setMessageBody:messageBody isHTML:NO];
    [mc setToRecipients:toRecipents];
    // attach NSData to message. Note: file name extension will be used by the mail client to launch
    // the handler with this extension in its info.plist.

    NSData *data = [[NSData alloc]init];
    data = [NSKeyedArchiver archivedDataWithRootObject:self.items];

    [mc addAttachmentData:data mimeType:@"application/CustomUTIHandler" fileName:@"traceData.nrc"];

    // Present mail view controller on screen
    [self presentViewController:mc animated:YES completion:NULL];

}

在发送之前存档的数组（NRCEventItem数组）：

    Printing description of self->_items:
<__NSArrayM 0x1c045e390>(
Event Date/time: 2017-12-29 00:08:17 +0000, Event Sender: <AppDelegate: 0x1c40523c0>, Event Description: appl did become active,
Event Date/time: 2017-12-29 00:15:32 +0000, Event Sender: <HourlyChimeTableViewController: 0x10282fa00>, Event Description: triggerNotification,
Event Date/time: 2017-12-29 00:30:32 +0000, Event Sender: <HourlyChimeTableViewController: 0x10282fa00>, Event Description: triggerNotification,
Event Date/time: 2017-12-29 00:45:32 +0000, Event Sender: <HourlyChimeTableViewController: 0x10282fa00>, Event Description: triggerNotification,
Event Date/time: 2018-01-05 00:00:32 +0000, Event Sender: <HourlyChimeTableViewController: 0x10282fa00>, Event Description: triggerNotification,
Event Date/time: 2018-01-05 00:15:32 +0000, Event Sender: <HourlyChimeTableViewController: 0x10282fa00>, Event Description: triggerNotification,
Event Date/time: 2018-01-05 00:30:32 +0000, Event Sender: <HourlyChimeTableViewController: 0x10282fa00>, Event Description: triggerNotification,
Event Date/time: 2018-01-05 00:45:32 +0000, Event Sender: <HourlyChimeTableViewController: 0x10282fa00>, Event Description: triggerNotification
)

EventItem类符合NSCoding：

    //
//  NRCEventItem.h
//  Hourly Chime2
//
//  Created by Nelson Capes on 12/12/17.
//  Copyright © 2017 Nelson Capes. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface NRCEventItem : NSObject <NSCoding>
@property (nonatomic) NSDate *eventDateTime;
@property (nonatomic) NSString *eventSender;
@property (nonatomic) NSString *eventDescription;
@end

接收应用的info.plist：

接收应用程序的代码，用于获取电子邮件附件并取消归档数据：

- (void) receiveNotificationFromAppDelegate:(NSNotification *) notification {
NSLog(@"userInfo trace %@",notification.userInfo[KTraceKey]);

self.items = (NSMutableArray*)[NSKeyedUnarchiver unarchiveObjectWithData:notification.userInfo[KTraceKey]];
[self.tableView reloadData];

}

取消归档后的数据：

    Printing description of path:
/private/var/mobile/Containers/Data/Application/CCDA0B96-8DD6-496E-B0A0-08B3C072E76A/Documents/Inbox/traceData-40.nrc
Printing description of items:
<__NSArrayM 0x1c4240720>(
Event Date/time: (null), Event Sender: (null), Event Description: (null),
Event Date/time: (null), Event Sender: (null), Event Description: (null),
Event Date/time: (null), Event Sender: (null), Event Description: (null),
Event Date/time: (null), Event Sender: (null), Event Description: (null),
Event Date/time: (null), Event Sender: (null), Event Description: (null),
Event Date/time: (null), Event Sender: (null), Event Description: (null),
Event Date/time: (null), Event Sender: (null), Event Description: (null),
Event Date/time: (null), Event Sender: (null), Event Description: (null)
)

显然，NSKeyedUnarchiver将数据识别为数组，并且数组中的元素是NRCEventItem。但是，数组的每个元素中的属性现在都是零。我还通过立即取消归档归档来测试归档步骤，并且阵列的属性与归档之前一样。

结论：不知何故，使用MFMailComposeViewController在传输过程中改变了数据。

如果有人能说清楚这一点，我会非常感激。

Answer 1

我发现了问题（而不是MFMailComposeViewController）。我的自定义类NRCEventItem没有实现NSCoding协议，因此包含它们的可变数组已正确存档和取消存档，但项目没有。以下是该项目的正确代码：

    //
//  NRCEventItem.m
//  Hourly Chime2
//
//  Created by Nelson Capes on 12/12/17.
//  Copyright © 2017 Nelson Capes. All rights reserved.
//

#import "NRCEventItem.h"
#import "constants.h"
@implementation NRCEventItem
-(void)encodeWithCoder:(NSCoder *)aCoder{

    [aCoder encodeObject:_eventSender forKey:kEventLoggerSender];
    [aCoder encodeObject:_eventDateTime forKey:KEventLoggerDateTime];
    [aCoder encodeObject:_eventDescription forKey:KEventLoggerEventDescription];

}
-(instancetype) initWithCoder:(NSCoder *)aDecoder{
    self = [super init];
    if (self){

        self.eventSender = [aDecoder decodeObjectForKey:kEventLoggerSender];
        self.eventDateTime = [aDecoder decodeObjectForKey:KEventLoggerDateTime];
        self.eventDescription = [aDecoder decodeObjectForKey:KEventLoggerEventDescription];

    }
    return self;
}
-(NSString *)description{
    return [NSString stringWithFormat:@"Event Date/time: %@, Event Sender: %@, Event Description: %@", self.eventDateTime, self.eventSender, self.eventDescription];
}
@end

我最后也改变了存档和解压缩的代码。这是有效的代码：

NSMutableData *data = [[NSMutableData alloc]init];
NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc]initForWritingWithMutableData:data];
[archiver encodeObject:self.items forKey:@"items"];
[archiver finishEncoding];

NSMutableData *data = [[NSMutableData alloc]init];
data = notification.userInfo[KTraceKey];
NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc]initForReadingWithData:data];
self.items = [unarchiver decodeObjectForKey:@"items"];
[unarchiver finishDecoding];

我发现使用NSKeyedArchiver和NSKeyedUnarchiver与encodeObject和decodeObject而不是archivedDataWithRootObject是有利的：如果你没有调用finishEncoding，unarchiver会告诉你档案中是否没有数据。使用根对象归档和取消归档后，您不会收到此通知。

我建议使用MFMailComposeViewController是一种在不同设备上运行的应用程序之间传输数据的简洁方法。关键是实现info.plist，它显示在我的OP中。

感谢Dave提出编码可能存在的问题！