App 终止时如何使用 NSUserDefault 保存自定义对象数组？

Question

因此，我尝试在应用程序终止时保存一个数组，以便在启动备份时可以重新填充该数组。不过，我遇到了很多不同的错误，主要是当我在应用程序启动时尝试重新创建数组时。我已采取步骤对自定义对象进行编码和解码，但也许我做得不正确...这是我的代码：

- (void)applicationWillTerminate:(UIApplication *)application
{
/*
 Called when the application is about to terminate.
 Save data if appropriate.
 See also applicationDidEnterBackground:.
 */

//Here is Where I save the array. "tasks is a pre-populated array of objects

NSData *taskData = [NSKeyedArchiver archivedDataWithRootObject:tasks];
[[NSUserDefaults standardUserDefaults]setObject:taskData forKey:@"tasks"];

}

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{

tasks = [[NSMutableArray alloc]init];

NSString *appDomain = [[NSBundle mainBundle] bundleIdentifier];
[[NSUserDefaults standardUserDefaults] removePersistentDomainForName:appDomain];

//NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];

if([[NSUserDefaults standardUserDefaults] objectForKey:@"tasks"]){

    NSData *tasksData = [[NSUserDefaults standardUserDefaults]objectForKey:@"tasks"];

 //It usually breaks right here

 tasks = [NSKeyedUnarchiver unarchiveObjectWithData:tasksData];

}

这是“tasks”数组包含的“Task”对象：

Task.h

#import <Foundation/Foundation.h>

@class TeamMember;
@class Project;


@interface Task : NSObject<NSCoding>{

NSDate *endDate;
NSDate *startDate;
NSMutableString* notes;
NSMutableString* taskName;
TeamMember *teamMember;
Project *project;
}
- (void)encodeWithCoder:(NSCoder *)encoder;
- (id)initWithCoder:(NSCoder *)decoder; 

@property  (nonatomic, retain)TeamMember *teamMember;
@property  (nonatomic, retain) Project * project;

@property (nonatomic, retain) NSMutableString *notes;
@property (nonatomic, retain) NSMutableString *taskName;
@property (nonatomic, retain) NSDate *startDate;
@property (nonatomic, retain) NSDate *endDate;


@end

Task。米

#import "Task.h"


@implementation Task
@synthesize notes;
@synthesize taskName;
@synthesize endDate;
@synthesize startDate;
@synthesize teamMember;
@synthesize project;


//@synthesize project;
- (void)encodeWithCoder:(NSCoder *)encoder {
//Encode properties, other class variables, etc
[encoder encodeObject:self.notes forKey:@"notes"];
[encoder encodeObject:self.taskName forKey:@"taskName"];
[encoder encodeObject:self.endDate forKey:@"endDate"];
[encoder encodeObject:self.startDate forKey:@"startDate"];

//you need to add in the encoding for teammember and project
}

- (id)initWithCoder:(NSCoder *)decoder {
if((self = [super init])) {
    //decode properties, other class vars
    self.notes = [decoder decodeObjectForKey:@"notes"];
    self.taskName = [decoder decodeObjectForKey:@"taskName"];
    self.endDate = [decoder decodeObjectForKey:@"endDate"];
    self.startDate = [decoder decodeObjectForKey:@"startDate"];

    //decode teamMember and Project here

}
}



@end

Answer 1

忽略将这样的数组保存到 NSUserDefaults 而不是使用 CoreData 的事实是糟糕的设计，您的问题是您没有同步默认值。在 applicationWillTerminate 方法的底部添加此行 [[NSUserDefaults standardUserDefaults] Synchronize]; 。

请使用 CoreData。用户默认值并不是用于数据持久性，它们旨在存储一些小数据块，例如布尔值或需要恢复的某些特定区域的宽度和高度，而不是实际上需要恢复的自定义用户内容坚持下来了。

另外，不要使用 applicationWillTerminate 方法作为保存数据的手段，应在用户添加数据后立即保存。此方法不保证其内容执行将正确完成。