目标C:自我与超级的区别

Question

我是Objective CI的新手,正在尝试一些示例程序.我无法理解自我和超级方法如何在目标C中工作.在下面的pgm中,CashTransaction.m [super trackSpending:amount]被调用并且在CreditCardTransaction.m中[self] trackspending:amount]被调用.我找不到self和super.super之间的区别用于调用基类重写方法.self用于调用子类重写方法.这就是我的理解.请纠正我,如果我错了.谢谢你.

的main.m

#import <Foundation/Foundation.h>
#import "BudgetObject.h"
#import "Transaction.h"
#import "CashTransaction.h"
#import "CreditCardTransaction.h"

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

        //!---Creating An Object And Allocating It With Values---
        Budget* budget = [Budget new];
        [budget createBudget:1000.00 withExchangeRate:1.2500];

        //!---Declaring And Adding Elements To An Array---
        NSMutableArray* transactions = [[NSMutableArray alloc] initWithCapacity:10];
        Transaction* aTransaction; 
        aTransaction = [Transaction new];
        [transactions addObject:aTransaction];

        //!---Calculating The No Of Elements In An Array---
        int k;
        k=[transactions count];
        NSLog(@"The count value is:%d",k);

        //!---Selecting According To The Type Of Transaction---
    for(Transaction *iTransaction in transactions){
         switch ([aTransaction returnType]) {
                case cash:
                        [budget spendDollars:[iTransaction returnAmount]];
                        break;
                case credit:
                        [budget changeForeignCurrency:[iTransaction returnAmount]];
                        break;
                default:
                        break;
         }
        }

        Budget* europeBudget = [Budget new];
        [europeBudget createBudget:1000.00 withExchangeRate:1.2500];

        Budget* englandBudget = [Budget new];
        [englandBudget createBudget:2000.00 withExchangeRate:1.5000];

        NSMutableArray* transactions = [[NSMutableArray alloc] initWithCapacity:10];
        Transaction* aTransaction;
        for(int n=1;n<2;n++){
                aTransaction = [CashTransaction new];
                [aTransaction createTransaction:n*100 forBudget:europeBudget];
                [transactions addObject:aTransaction];

                aTransaction = [CashTransaction new];
                [aTransaction createTransaction:n*100 forBudget:englandBudget];
                [transactions addObject:aTransaction];  
        }
        int n=1;
        while (n<4) {
                aTransaction = [CreditCardTransaction new];
                [aTransaction createTransaction:n*100 forBudget:europeBudget];
                [transactions addObject:aTransaction];

                aTransaction = [CreditCardTransaction new];
                [aTransaction createTransaction:n*100 forBudget:englandBudget];
                [transactions addObject:aTransaction];

                n++;    
        }
        for(Transaction* aTransaction in transactions){
                [aTransaction spend];
        }
return 0;
}

BudgetObject.h

#import <Cocoa/Cocoa.h>
@interface Budget : NSObject {
        float exchangeRate;
        double budget;
        double exchangeTransaction;
}
- (void) createBudget: (double) aBudget withExchangeRate: (float) anExchangeRate;
- (void) spendDollars: (double) dollars;
- (void) changeForeignCurrency: (double) foreignCurrency;
@end

BudgetObject.m

#import "BudgetObject.h"
@implementation Budget
- (void) createBudget: (double) aBudget withExchangeRate: (float) anExchangeRate;
{
        budget = aBudget;
        exchangeRate = anExchangeRate;
}
- (void) spendDollars: (double) dollars
{
        budget = budget - dollars;
        NSLog(@"Converting %0.2f into U.S Foreign Currency leaves $%0.2f",dollars,budget);
}
- (void) changeForeignCurrency: (double) foreignCurrency
{
        exchangeTransaction = foreignCurrency * exchangeRate;
        budget = budget - exchangeTransaction;
        NSLog(@"Charging %0.2f in Foreign Currency leaves $%0.2f",foreignCurrency,budget);
}
@end

Transaction.h

#import <Cocoa/Cocoa.h>
#import "BudgetObject.h"
@class Budget;
@interface Transaction : NSObject {
        Budget* budget;
        double amount;  
}
- (void) createTransaction: (double) theAmount forBudget: (Budget*) aBudget;
- (void) trackSpending: (double) theAmount;
- (void) spend;
@end

Transaction.m

#import "Transaction.h"
#import "BudgetObject.h"
@implementation Transaction
- (void) createTransaction: (double) theAmount forBudget: (Budget*) anBudget {
        budget = anBudget;
        amount = theAmount;
}
- (void) spend {

}
-(void) trackSpending: (double) theAmount {
        NSLog(@"You are about to spend another %0.2f",theAmount);
}
@end

CashTransaction.h

#import <Cocoa/Cocoa.h>
#import "Transaction.h"
@interface CashTransaction : Transaction {

}
@end

CashTransaction.m

#import "CashTransaction.h"
#import "BudgetObject.h"
@implementation CashTransaction
- (void) spend{
        [super trackSpending:amount];
        [budget spendDollars:amount];
}
@end

CreditCardTransaction.h

#import <Cocoa/Cocoa.h>
#import "Transaction.h"
@interface CreditCardTransaction : Transaction {

}
@end

CreditCardTransaction.m

#import "CreditCardTransaction.h"
#import "BudgetObject.h"
@implementation CreditCardTransaction
- (void) spend {
        [self trackSpending:amount];
        [budget changeForeignCurrency:amount];
}
@end

输出:

2011-04-15 11:24:46.112 Bud Obj1[1041:a0f] You are about to spend another 100.00
2011-04-15 11:24:46.114 Bud Obj1[1041:a0f] Converting 100.00 into U.S Foreign Currency leaves $900.00
2011-04-15 11:24:46.115 Bud Obj1[1041:a0f] You are about to spend another 100.00
2011-04-15 11:24:46.115 Bud Obj1[1041:a0f] Converting 100.00 into U.S Foreign Currency leaves $1900.00
2011-04-15 11:24:46.116 Bud Obj1[1041:a0f] You are about to spend another 100.00
2011-04-15 11:24:46.119 Bud Obj1[1041:a0f] Charging 100.00 in Foreign Currency leaves $775.00
2011-04-15 11:24:46.120 Bud Obj1[1041:a0f] You are about to spend another 100.00
2011-04-15 11:24:46.120 Bud Obj1[1041:a0f] Charging 100.00 in Foreign Currency leaves $1750.00
2011-04-15 11:24:46.121 Bud Obj1[1041:a0f] You are about to spend another 200.00
2011-04-15 11:24:46.121 Bud Obj1[1041:a0f] Charging 200.00 in Foreign Currency leaves $525.00
2011-04-15 11:24:46.122 Bud Obj1[1041:a0f] You are about to spend another 200.00
2011-04-15 11:24:46.122 Bud Obj1[1041:a0f] Charging 200.00 in Foreign Currency leaves $1450.00
2011-04-15 11:24:46.123 Bud Obj1[1041:a0f] You are about to spend another 300.00
2011-04-15 11:24:46.123 Bud Obj1[1041:a0f] Charging 300.00 in Foreign Currency leaves $150.00
2011-04-15 11:24:46.124 Bud Obj1[1041:a0f] You are about to spend another 300.00
2011-04-15 11:24:46.125 Bud Obj1[1041:a0f] Charging 300.00 in Foreign Currency leaves $1000.00

Answer 1

self并且super工作方式完全不同:self表示运行时的调用对象,同时super表示方法定义所在的类的超类.在两种情况下,它们都指定搜索方法应该从哪里开始,在self起始点是动态确定的super情况下,如果在编译时已知.

这是一个组成的例子:

@interface Grandparent : NSObject

- (void) One;

@end

@implementation Grandparent

- (void) One { NSLog(@"Grandparent One\n"); }

@end

@interface Parent : Grandparent

- (void) One;
- (void) Two;

@end

@implementation Parent

- (void) One { NSLog(@"Parent One\n"); }

- (void) Two
{
    [self One];                 // will call One based on the calling object
    [super One];                // will call One based on the defining object - Parent in this case so will Grandparent's One
}

@end

@interface Child : Parent

- (void) One;

@end

@implementation Child

- (void) One { NSLog(@"Child One\n"); }

@end


@implementation FamilyAppDelegate

@synthesize window;

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    Child *c = [Child new];
    [c Two];                            // will call the Two inherited from Parent

    Parent *p = [Parent new];
    [p Two];                            // will call Parent's Two
}

@end

所以我们有三个班级; Grandparent,Parent和Child; 每个都有一个方法One.类Parent has a method两个which calls一个on自我andsuper`.运行它会产生:

2011-04-15 22:49:05.006 Family[1993:a0f] Child One
2011-04-15 22:49:05.009 Family[1993:a0f] Grandparent One
2011-04-15 22:49:05.009 Family[1993:a0f] Parent One
2011-04-15 22:49:05.010 Family[1993:a0f] Grandparent One

对于Child情况下,呼叫[c Two]调用该方法Two是Child从它继承了Parent-所以我们必须继承.

现在,作为Two执行它首先调用[self One]和self是一个实例Child,其中有一个One,这样Child的One执行-这是基于继承的多态性; 在规定时间Parent的Two未来存在Child是未知的,但在执行时调用[self One]能够调用Child的方法.

接下来的电话Two是[super One].这是现在已知是指Grandparent的One在定义的时间.

通常super不引用超类中的方法(就像在本例中那样),但是对于方法,类型为超类的对象将调用,例如,它可以属于Greatgrandparent.但是,无论调用什么方法都可以在编译时确定,因为任何类的祖先都是已知的.

这些电话[self *method*]和[super *method*]甚至可以调用相同的方法,在前者的情况下动态发现的,而在后一种静态已知.

希望你现在可以申请继承,self并super举例说明.