iphone - 如何将 plist 保存到 NSUserDefaults

Question

我正在尝试将我创建的 .plist 保存到我的 NSUserDefaults 中，这样我就可以保存我放入其中的数据，所以如果应用程序是停止(从多任务栏中删除)我不会丢失这些值。

我已被指向本教程 here

里面有这个示例代码。

-(void)saveToUserDefaults:(NSString*)myString
{
    NSUserDefaults *standardUserDefaults = [NSUserDefaults standardUserDefaults];

    if (standardUserDefaults) {
        [standardUserDefaults setObject:myString forKey:@"Prefs"];
        [standardUserDefaults synchronize];
    }
}

-(NSString*)retrieveFromUserDefaults
{
    NSUserDefaults *standardUserDefaults = [NSUserDefaults standardUserDefaults];
    NSString *val = nil;

    if (standardUserDefaults) 
        val = [standardUserDefaults objectForKey:@"Prefs"];

    return val;
}

我需要帮助的是上述内容与保存 .plists 有何关系？

我有一个 .plist Controller 类，它读取包 .plist 在根文档中创建一个新的 .plist 然后读写到那......我怎么用上面的来保存它当应用程序退出还是关闭？

这就是我加载和写入我的 .plist 的方式，目前使用单例并且它在自己的类中。

#pragma mark Singleton Methods
+ (id)sharedManager {
    @synchronized(self) {
        if (sharedMyManager == nil)
            sharedMyManager = [[self alloc] init];
    }
    return sharedMyManager;
}
- (id)init {
    if (self = [super init]) {

        // Data.plist code
        // get paths from root direcory
        NSArray *paths = NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES);
        // get documents path
        NSString *documentsPath = [paths objectAtIndex:0];
        // get the path to our Data/plist file
        NSString *plistPath = [documentsPath stringByAppendingPathComponent:@"EngineProperties.plist"];

        // check to see if Data.plist exists in documents
        if (![[NSFileManager defaultManager] fileExistsAtPath:plistPath])
        {
            // if not in documents, get property list from main bundle
            plistPath = [[NSBundle mainBundle] pathForResource:@"EngineProperties" ofType:@"plist"];
        }

        // read property list into memory as an NSData object
        NSData *plistXML = [[NSFileManager defaultManager] contentsAtPath:plistPath];
        NSString *errorDesc = nil;
        NSPropertyListFormat format;
        // convert static property liost into dictionary object
        NSDictionary *tempRoot = (NSMutableDictionary *)[NSPropertyListSerialization propertyListFromData:plistXML mutabilityOption:NSPropertyListMutableContainersAndLeaves format:&format errorDescription:&errorDesc];
        if (!tempRoot)
        {
            NSLog(@"Error reading plist: %@, format: %d", errorDesc, format);
        }
        // assign values
        self.signature = [tempRoot objectForKey:@"Signature"];
        self.version = [tempRoot objectForKey:@"Version"];
        self.request = [tempRoot objectForKey:@"Request"];
        self.dataVersion = [tempRoot objectForKey:@"Data Version"];

        man = [cacheValue objectForKey:@"Man"];
        mod = [cacheValue objectForKey:@"Mod"];
        sub = [cacheValue objectForKey:@"SubMod"];

        cacheValue = [tempRoot objectForKey:@"Cache Value"];
    }


    - (void) saveData:(NSString *)methodName signature:(NSString *)pSignature Version:(NSNumber *)pVersion request:(NSNumber *)rNumber dataVersion:(NSNumber *)dvReturned cacheValue:(NSNumber *)cValue;
    {
        // get paths from root direcory
        NSArray *paths = NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES);
        // get documents path
        NSString *documentsPath = [paths objectAtIndex:0];
        // get the path to our Data/plist file
        NSString *plistPath = [documentsPath stringByAppendingPathComponent:@"EngineProperties.plist"];

        // set the variables to the values in the text fields
        self.signature = pSignature;
        self.version = pVersion;
        self.request = rNumber;
        self.dataVersion = dvReturned;

        //do some if statment stuff here to put the cache in the right place or what have you.
        if (methodName == @"manufacturers")
        {
            self.man = cValue; 
        }
        else if (methodName == @"models")
        {
            self.mod = cValue;
        }
        else if (methodName == @"subMod")
        {
            self.sub = cValue;
        }

        self.cacheValue = [NSDictionary dictionaryWithObjectsAndKeys:
                           man, @"Manufacturers",
                           mod, @"Models",
                           sub, @"SubModels", nil];


        NSDictionary *plistDict = [NSDictionary dictionaryWithObjectsAndKeys:
                                   signature, @"Signature",
                                   version, @"Version",
                                   request, @"Request",
                                   dataVersion, @"Data Version",
                                   cacheValue, @"Cache Value", nil];



        NSString *error = nil;
        // create NSData from dictionary
        NSData *plistData = [NSPropertyListSerialization dataFromPropertyList:plistDict format:NSPropertyListXMLFormat_v1_0 errorDescription:&error];

        // check is plistData exists
        if(plistData)
        {
            // write plistData to our Data.plist file
            [plistData writeToFile:plistPath atomically:YES];

            NSString *myString = [[NSString alloc] initWithData:plistData encoding:NSUTF8StringEncoding];
            //        NSLog(@"%@", myString);
        }
        else
        {
            NSLog(@"Error in saveData: %@", error);
            //        [error release];
        }
    }


    @end

Answer 1

你不能将 .plist 写入 NSUserDefaults，至少实际上不行。为此，您必须将 .plist 中的特定键写入 NSUserDefaults，这基本上就像保存所有数据的两个副本。您可以将 NSUserDefaults 视为一个不可见的 .plist，您可以对其进行读取和写入，而无需实际查看该文件。使用 NSUserDefaults，即使应用在多任务处理中被终止，您也可以恢复保存的值。

但是，您如何在 .plist 和 NSUserDefaults 之间进行选择应该基于您需要保存多少数据。 Apple 建议只将少量数据保存到 NSUserDefaults。如果您需要保存大量信息，那么 .plist 是最佳选择。或者当然是 Core-Data。