61，[phrase writeToFile: @"/tmp/verbiage.txt"  atomically: YES];的atomically 是用于通知cocoa是否應(yīng)該首先將文件內(nèi)容保存在臨時(shí)文件中，當(dāng)文件保存成功后，再將該臨時(shí)文件和原始文件交換


62，編碼對(duì)象

#import <Foundation/Foundation.h>


@interface Thingie : NSObject <NSCoding> {

    NSString *name;

    int magicNumber;

    float shoeSize;

    NSMutableArray *subThingies;

}

@property (copy) NSString *name;

@property int magicNumber;

@property float shoeSize;

@property (retain) NSMutableArray *subThingies;


- (id)initWithName: (NSString *) n

       magicNumber: (int) mn  

          shoeSize: (float) ss;


@end // Thingie



@implementation Thingie

@synthesize name;

@synthesize magicNumber;

@synthesize shoeSize;

@synthesize subThingies;


- (id)initWithName: (NSString *) n

       magicNumber: (int) mn  

          shoeSize: (float) ss {

    if (self = [super init]) {

        self.name = n;

        self.magicNumber = mn;

        self.shoeSize = ss;

        self.subThingies = [NSMutableArray array];

    }

    return (self);

}


- (void) dealloc {

    [name release];

    [subThingies release];

    [super dealloc];

   

} // dealloc


- (NSString *) description {

    NSString *description =

    [NSString stringWithFormat: @"%@: %d/%.1f %@",

     name, magicNumber, shoeSize, subThingies];

    return (description);

   

} // description


- (void) encodeWithCoder: (NSCoder *) coder {

    [coder encodeObject: name

forKey: @"name"];

    [coder encodeInt: magicNumber

  forKey: @"magicNumber"];

    [coder encodeFloat: shoeSize

forKey: @"shoeSize"];

    [coder encodeObject: subThingies

forKey: @"subThingies"];

   

} // encodeWithCoder



- (id) initWithCoder: (NSCoder *) decoder {

    if (self = [super init]) {

        self.name = [decoder decodeObjectForKey: @"name"];

        self.magicNumber = [decoder decodeIntForKey: @"magicNumber"];

        self.shoeSize = [decoder decodeFloatForKey: @"shoeSize"];

        self.subThingies = [decoder decodeObjectForKey: @"subThingies"];

    }

    return (self);

} // initWithCoder


@end // Thingie



int main (int argc, const char * argv[]) {

    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

Thingie *thing1;

thing1 = [[Thingie alloc]

  initWithName: @"thing1"

  magicNumber: 42

  shoeSize: 10.5];

NSLog (@"some thing: %@", thing1);


// 使用NSData的兩個(gè)子類NSKeyedArchiver和NSKeyedUnarchiver

    NSData *freezeDried;

    freezeDried = [NSKeyedArchiver archivedDataWithRootObject: thing1];

    [thing1 release];

    thing1 = [NSKeyedUnarchiver unarchiveObjectWithData: freezeDried];

    NSLog (@"reconstituted thing: %@", thing1);

   

    Thingie *anotherThing;

    anotherThing =  [[[Thingie alloc]

  initWithName: @"thing2"

  magicNumber: 23

  shoeSize: 13.0] autorelease];

    [thing1.subThingies addObject: anotherThing];

    anotherThing =  [[[Thingie alloc]

  initWithName: @"thing3"

  magicNumber: 17

  shoeSize: 9.0] autorelease];

    [thing1.subThingies addObject: anotherThing];

    NSLog (@"thing with things: %@", thing1);

    freezeDried = [NSKeyedArchiver archivedDataWithRootObject: thing1];

    thing1 = [NSKeyedUnarchiver unarchiveObjectWithData: freezeDried];

    NSLog (@"reconstituted multithing: %@", thing1);

    [thing1.subThingies addObject: thing1];

    // You really don't want to do this...

    // NSLog (@"infinite thinging: %@", thing1);

    freezeDried = [NSKeyedArchiver archivedDataWithRootObject: thing1];

[freezeDried writeToFile:@"/tmp/xiaoyuan" atomically:YES];

    thing1 = [NSKeyedUnarchiver unarchiveObjectWithData: freezeDried];

   

    [pool release];

    return (0);

} // main


63，KVC(Key Value Code)

Advantage one:

NSLog (@"horsepower is %@", [engine valueForKey: @"horsepower"]); //這個(gè)會(huì)自動(dòng)打包成NSNumber或NSValue

[engine setValue: [NSNumber numberWithInt: 150] //這個(gè)使用的時(shí)候要自己打包

  forKey: @"horsepower"];

NSLog (@"horsepower is %@", [engine valueForKey: @"horsepower"]);

[car setValue: [NSNumber numberWithInt: 155]

  forKeyPath: @"engine.horsepower"];//路徑的獲得

NSLog (@"horsepower is %@", [car valueForKeyPath: @"engine.horsepower"]);

NSArray *pressures = [car valueForKeyPath: @"tires.pressure"];//要是路徑是一個(gè)數(shù)組就只能獲取一個(gè)數(shù)組，不能只獲取一個(gè)

NSLog (@"pressures %@", pressures);


Advantage two

NSNumber *count;

count = [garage valueForKeyPath: @"cars.@count"];

NSLog (@"We have %@ cars", count);

NSNumber *sum;

sum = [garage valueForKeyPath: @"cars.@sum.mileage"];

NSLog (@"We have a grand total of %@ miles", sum);

NSNumber *avgMileage;

avgMileage = [garage valueForKeyPath: @"cars.@avg.mileage"];

NSLog (@"average is %.2f", [avgMileage floatValue]);

NSNumber *min, *max;

min = [garage valueForKeyPath: @"cars.@min.mileage"];

max = [garage valueForKeyPath: @"cars.@max.mileage"];

NSLog (@"minimax: %@ / %@", min, max);

NSArray *manufacturers;

manufacturers = [garage valueForKeyPath: @"cars.@distinctUnionOfObjects.make"];

NSLog (@"makers: %@", manufacturers);

//另外，union 運(yùn)算符指一組對(duì)象的并集

//distinct用于刪除重復(fù)的內(nèi)容

//遺憾的一點(diǎn)就是不能添加自的運(yùn)算符


Advantage three

car = [[garage valueForKeyPath: @"cars"] lastObject];

NSArray *keys = [NSArray arrayWithObjects: @"make", @"model", @"modelYear", nil];

NSDictionary *carValues = [car dictionaryWithValuesForKeys: keys];

NSLog (@"Car values : %@", carValues);

NSDictionary *newValues =

[NSDictionary dictionaryWithObjectsAndKeys:

@"Chevy", @"make",

@"Nova", @"model",

[NSNumber numberWithInt:1964], @"modelYear",

[NSNull null], @"mileage",

nil];

[car setValuesForKeysWithDictionary: newValues];

NSLog (@"car with new values is %@", car);

//新裝配過的car


KVC的一些特殊情況處理

case one: nil的處理

[car setValue:nil forKey: @"mileage"];

NSLog (@"Nil miles are %@", car.mileage);

這里的標(biāo)量值mileage中的nil表示的是什么0？－1？pi？cocoa無法知道，可以再car類里面重寫

- (void) setNilValueForKey: (NSString *) key {

if ([key isEqualToString: @"mileage"]) {

mileage = 0;

} else {

[super setNilValueForKey: key];

}

} // setNilValueForKey


case two：未定義的健的處理

在控制類里面寫

- (void) setValue: (id) value  forUndefinedKey: (NSString *) key {

if (stuff == nil) {

stuff = [[NSMutableDictionary alloc] init];

}

[stuff setValue: value forKey: key];

} // setValueForUndefinedKey



- (id) valueForUndefinedKey:(NSString *)key {

id value = [stuff valueForKey: key];

return (value);

} // valueForUndefinedKey