iphone - plist 值丢失

Question

好的，过去 2 天我一直在努力解决这个问题。我有一个控制我的属性列表的类，它用作单例类，因此它只实例化一次，并且其中有另一个方法用于将值保存到 plist。

无论您做什么，plist 都能很好地工作，直到您从多任务栏中删除应用程序(即完全关闭应用程序)，然后 plist 中的所有值都重置为 null。但是 plist 并没有丢失。

所以我现在在想，也许我正在覆盖我在根文档目录中为读取和写入功能而创建的 plist 中的值。我希望通过我的代码示例你们可以发现我的错误......我不确定我还需要添加什么..如果你有任何问题可以帮助我回答这个问题那么请让我知道。

如有任何帮助，我们将不胜感激，我的 child 的 child 的 children 将向您首次亮相。

#import "EnginePropertiesController.h"

static EnginePropertiesController *sharedMyManager = nil;

@implementation EnginePropertiesController

@synthesize pSignature;
@synthesize pVersion;
@synthesize rNumber;
@synthesize dVReturned;
@synthesize cacheValue;

@synthesize manu;
@synthesize mod;
@synthesize submod;


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

            // 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"];
            NSLog(@"myplist path read = %@", plistPath);

            // 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];
            manu = [cacheValue objectForKey:@"Manu"];
            mod = [cacheValue objectForKey:@"Mod"];
            submod = [cacheValue objectForKey:@"SubMod"];
            if (tempRoot && [tempRoot count]){
                // assign values
                self.pVersion = [tempRoot objectForKey:@"PSignature"];
                self.pVersion = [tempRoot objectForKey:@"PVersion"];
                self.rNumber = [tempRoot objectForKey:@"RNumber"];
                self.dVReturned = [tempRoot objectForKey:@"DVReturned"];
                cacheValue = [tempRoot objectForKey:@"Cache Value"];
        }
    }
    return self;
}

- (void) saveData:(NSString *)methodName pSignature:(NSString *)TemppSignature pVersion:(NSNumber *)TemppVersion rNumber:(NSNumber *)TemprNumber dVReturned:(NSNumber *)TempdvReturned 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.pSignature = TemppSignature;
    self.pVersion = TemppVersion;
    self.rNumber = TemprNumber;
    self.dVReturned = TempdVReturned;

    //This checks with methodName I would like to save the value from
    //The reason for this is there are 3 different cache values I get at seperate times to save This if statment just makes sure they are in the correct order.
    if ([methodName isEqualToString:@"Getmanu"]) {
        self.manu = cValue; 
    } else if ([methodName isEqualToString:@"GetMod"]) {
        self.mod = cValue;
    } else if ([methodName isEqualToString:@"GetSubMod"]) {
        self.submod = cValue;
    }        

    //Set up cacheValue Dictionary that will be added to the property list root dictionary
    self.cacheValue = [NSDictionary dictionaryWithObjectsAndKeys:
                       manu, @"Manu",
                       mod, @"Mod",
                       subMod, @"SubMod", nil];

    //Pass appropriate values into plist
    NSDictionary *plistDict = [NSDictionary dictionaryWithObjectsAndKeys:
                               protocolSignature, @"Protocol Signature",
                               pVersion, @"Protocol Version",
                               rNumber, @"Request Number",
                               dVReturned, @"Data Version returned",
                               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];
    } else {
        NSLog(@"Error in saveData: %@", error);
    }
}


@end

Answer 1

问题:零值

这里有一个问题:pVersion 被分配了两次，而 pSignature 仍然是 nil。

self.pVersion = [tempRoot objectForKey:@"PSignature"];
self.pVersion = [tempRoot objectForKey:@"PVersion"];

应该是这样

self.pSignature = [tempRoot objectForKey:@"PSignature"];
self.pVersion = [tempRoot objectForKey:@"PVersion"];

这反过来会导致节省时间的麻烦:

NSDictionary *plistDict = [NSDictionary dictionaryWithObjectsAndKeys:
                           pSignature, @"PSignature",
                           pVersion, @"PVersion",
                           rNumber, @"RNumber",
                           dVReturned, @"DVReturned",
                           cacheValue, @"Cache Value", nil];

这个构造函数不知道它有多少个参数，它只是一直运行直到遇到 nil。如果 pSignature 为 nil，它将保存一个空字典。

修复:强大的 NSDictionary 创建

虽然直接的解决方案是修复 pSignature 读取，但使用 dictionaryWithObjectsAndKeys: 构建字典总是很脆弱。最好使用 setObject:forKey 单独存储每个对象。如果对象为 nil，则会抛出异常，因此在调用之前进行测试。

NSMutableDictionary *plistDict = [NSMutableDictionary dictionary];
if (pSignature) [plistDict setObject:pSignature forKey:@"PSignature"];
if (pVersion) [plistDict setObject:pVersion forKey:@"PVersion"];
// ... and so on.

备选方案:NSCoding

存储的另一种选择是序列化。查看Archives and Serializations Programming Guide .这需要权衡:虽然保存和加载在工作时更简单，但生成的文件的可读性较差。

调试

最后，三个地方可以放置日志语句、断点或对话框，以帮助解决此类情况:

1. 记录正在加载的词典和正在保存的词典。如果您打开您的应用程序并立即触发保存，这些词典是否相同？
2. 检查发送到 nil 终止方法的第一个参数，例如 arrayWithObjects: 和 dictionaryWithObjectsAndKeys:
3. 在模拟器上，记录用于保存的路径并在 Finder 中打开它。那里有文件吗？如果是属性列表，您可以在 XCode 中打开它，看看它是否包含您期望的内容。