iphone - 在我将它们保存到 plist 之前，变量失去了它们的值

Question

我正在为我的 plist 编写一个 Controller 类，它被另一个类调用。 controller 类有一个 read 和 save 方法，read 方法打开 plist 并将其保存到文档文件中以供读写。在这个读取类中，我将之前保存的所有值放入它们自己的变量中。

然后在从另一个类调用的 Save 方法调用中，所有值都作为参数传入，然后从那里我将新值传递给正确的变量并将其传递给 plist.. 但是我有一个字典在我的 plist 中，它只保存一个值并将其他值重置为空。我想知道如何确保这些变量保持它们的值？

这是我的.h

#import <Foundation/Foundation.h>

@interface EngineProperties : NSObject {

NSString *signature;
NSNumber *version;
NSNumber *request;
NSNumber *dataVersion;
NSMutableDictionary *cacheValue;
//cachevalue Items
NSNumber *man;
NSNumber *mod;
NSNumber *sub;

}

@property (copy, nonatomic) NSString *signature;
@property (copy, nonatomic) NSNumber *version;
@property (copy, nonatomic) NSNumber *request;
@property (copy, nonatomic) NSNumber *dataVersion;
@property (copy, nonatomic) NSMutableDictionary *cacheValue;
//cachevalue Items
@property (copy, nonatomic) NSNumber *man;
@property (copy, nonatomic) NSNumber *mod;
@property (copy, nonatomic) NSNumber *sub;



- (void) readPlistData;
- (void) saveData:(NSString *)methodName signature:(NSString *)pSignature Version:(NSNumber *)pVersion request:(NSNumber *)rNumber dataVersion:(NSNumber *)dvReturned cacheValue:(NSNumber *)cValue;

@end

这是我的.m

#import "EngineProperties.h"

@implementation EngineProperties

@synthesize signature;
@synthesize version;
@synthesize request;
@synthesize dataVersion;
@synthesize cacheValue;

@synthesize man;
@synthesize mod;
@synthesize sub;



//This opens up and reads the current plist ready to be used
-(void) readPlistData
{
    // 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

我试图找出如何在这三个变量 man、mod、sub 中保持正确的值，以便我可以将它们放入我的缓存值字典中。

Answer 1

问题是当您准备好数据以创建字典时，这里:

if (methodName == @"manufacturers")
{
    self.man = cValue; 
}
else if (methodName == @"models")
{
    self.mod = cValue;
}
else if (methodName == @"subMod")
{
    self.sub = cValue;
}

这不是比较字符串的正确方法(你实际上是在比较字符串的地址，所以它们可能永远不会相同)，你应该使用这个:

if ([methodName isEqualToString:@"manufacturers"])
{
    self.man = cValue; 
}
else if ([methodName isEqualToString:@"models"])
{
    self.mod = cValue;
}
else if ([methodName isEqualToString:@"subMod"])
{
    self.sub = cValue;
}

另一个问题是，在 readPlistData 中，您正在读取键“Man”、“Mod”和“SubMod”，但它们应该与您写入字典的内容相同:“Manufacturers”、“Models”和“子模型”。 (任何一个都可能是正确的，但它们需要匹配，以便您读取和写入相同的 key !)

最后，您是在每次调用 saveData 时都使用相同的 EngineProperties 实例，还是每次都创建一个新对象？如果您使用的不是同一个对象，则每次调用它时 iVars 都会重置为 nil。