大書呆子牧場目標-c：第18章 - 繼承

Question

我目前正在通過「大書呆子牧場」的書中學習Objective-C。我已經重複了第18章的代碼，但是我收到了錯誤。使用64位macos 10.6女巫實際版本的xcode。

編譯器說：

Build target BMITime

CompileC /Users/pm/Library/Developer/Xcode/DerivedData/BMITime-cjqpmtvlmdoeiecyxbofznzjgpij/Build/Intermediates/BMITime.build/Debug/BMITime.build/Objects-normal/x86_64/main.o BMITime/main.m normal x86_64 objective-c com.apple.compilers.llvm.clang.1_0.compiler cd /Users/pm/Dropbox/objective-c/BMITime setenv LANG en_US.US-ASCII /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -x objective-c -arch x86_64 -fmessage-length=0 -std=gnu99 -fobjc-arc -Wno-trigraphs -fpascal-strings -O0 -Wno-missing-field-initializers -Wno-missing-prototypes -Wreturn-type -Wno-implicit-atomic-properties -Wformat -Wno-missing-braces -Wparentheses -Wswitch -Wno-unused-function -Wno-unused-label -Wno-unused-parameter -Wunused-variable -Wunused-value -Wuninitialized -Wno-unknown-pragmas -Wno-shadow -Wno-four-char-constants -Wno-sign-compare -Wshorten-64-to-32 -Wpointer-sign -Wno-newline-eof -Wno-selector -Wno-strict-selector-match -Wno-undeclared-selector -Wno-deprecated-implementations -DDEBUG=1 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.7.sdk -fasm-blocks -Wprotocol -Wdeprecated-declarations -mmacosx-version-min=10.7 -g -Wno-conversion -Wno-sign-conversion "-DIBOutlet=attribute((iboutlet))" "-DIBOutletCollection(ClassName)=attribute((iboutletcollection(ClassName)))" "-DIBAction=void)attribute((ibaction)" -iquote /Users/pm/Library/Developer/Xcode/DerivedData/BMITime-cjqpmtvlmdoeiecyxbofznzjgpij/Build/Intermediates/BMITime.build/Debug/BMITime.build/BMITime-generated-files.hmap -I/Users/pm/Library/Developer/Xcode/DerivedData/BMITime-cjqpmtvlmdoeiecyxbofznzjgpij/Build/Intermediates/BMITime.build/Debug/BMITime.build/BMITime-own-target-headers.hmap -I/Users/pm/Library/Developer/Xcode/DerivedData/BMITime-cjqpmtvlmdoeiecyxbofznzjgpij/Build/Intermediates/BMITime.build/Debug/BMITime.build/BMITime-all-target-headers.hmap -iquote /Users/pm/Library/Developer/Xcode/DerivedData/BMITime-cjqpmtvlmdoeiecyxbofznzjgpij/Build/Intermediates/BMITime.build/Debug/BMITime.build/BMITime-project-headers.hmap -I/Users/pm/Library/Developer/Xcode/DerivedData/BMITime-cjqpmtvlmdoeiecyxbofznzjgpij/Build/Products/Debug/include -I/Users/pm/Library/Developer/Xcode/DerivedData/BMITime-cjqpmtvlmdoeiecyxbofznzjgpij/Build/Intermediates/BMITime.build/Debug/BMITime.build/DerivedSources/x86_64 -I/Users/pm/Library/Developer/Xcode/DerivedData/BMITime-cjqpmtvlmdoeiecyxbofznzjgpij/Build/Intermediates/BMITime.build/Debug/BMITime.build/DerivedSources -F/Users/pm/Library/Developer/Xcode/DerivedData/BMITime-cjqpmtvlmdoeiecyxbofznzjgpij/Build/Products/Debug -include /Users/pm/Library/Developer/Xcode/DerivedData/BMITime-cjqpmtvlmdoeiecyxbofznzjgpij/Build/Intermediates/PrecompiledHeaders/BMITime-Prefix-bbjacqhmgaerfrhblktcvkpzzntb/BMITime-Prefix.pch -MMD -MT dependencies -MF /Users/pm/Library/Developer/Xcode/DerivedData/BMITime-cjqpmtvlmdoeiecyxbofznzjgpij/Build/Intermediates/BMITime.build/Debug/BMITime.build/Objects-normal/x86_64/main.d --serialize-diagnostics /Users/pm/Library/Developer/Xcode/DerivedData/BMITime-cjqpmtvlmdoeiecyxbofznzjgpij/Build/Intermediates/BMITime.build/Debug/BMITime.build/Objects-normal/x86_64/main.dia -c /Users/pm/Dropbox/objective-c/BMITime/BMITime/main.m -o /Users/pm/Library/Developer/Xcode/DerivedData/BMITime-cjqpmtvlmdoeiecyxbofznzjgpij/Build/Intermediates/BMITime.build/Debug/BMITime.build/Objects-normal/x86_64/main.o

/Users/pm/Dropbox/objective-c/BMITime/BMITime/main.m:21:10: error: no visible @interface for 'Employee' declares the selector 'setWeightInKilos:' [person setWeightInKilos:96]; ^/Users/pm/Dropbox/objective-c/BMITime/BMITime/main.m:22:10: error: no visible @interface for 'Employee' declares the selector 'setHeightInMeters:' [person setHeightInMeters:1.8]; ^/Users/pm/Dropbox/objective-c/BMITime/BMITime/main.m:26:22: error: no visible @interface for 'Employee' declares the selector 'bodyMassIndex' float bmi = [person bodyMassIndex]; ^3 errors generated.

我的代碼看起來是這樣的：

的main.m

#import <Foundation/Foundation.h> 
#import "Employee.h" 

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

    @autoreleasepool { 

     // Erstellt eine Instanz von Person 
     Employee *person = [[Employee alloc] init]; 

     // Gibt den Instanzvariablen interessante Werte 
     [person setWeightInKilos:96]; 
     [person setHeightInMeters:1.8]; 
     [person setEmployeeID:15]; 

     // Ruft die Methode bodyMassIndex auf 
     float bmi = [person bodyMassIndex]; 
     NSLog(@"Employee %d has a BMI of %f", [person employeeID], bmi); 


    } 
    return 0; 
} 

Person.h

#import <Foundation/Foundation.h> 

// Die Klasse Person erbt alle Instanzvariablen 
// und Methoden, die von der Klasse NSObject definiert wurden 
@interface Person : NSObject 
{ 
    // Sie hat zwei Instanzvariablen 
    float heightInMeters; 
    int weightInKilos; 
} 
@property float heightInMeters; 
@property int weightInKilos; 

// Diese Methode berechnet den Body-Mass-Index 
- (float)bodyMassIndex; 
@end 

Employee.h

#import <Foundation/Foundation.h> 
#import "Person.h" 

@interface Employee : NSObject 
{ 
    int employeeID; 
} 
@property int employeeID; 
@end 

Employee.m

#import "Employee.h" 

@implementation Employee 

@synthesize employeeID; 

@end 

Person.m

#import "Person.h" 

@implementation Person 

@synthesize heightInMeters, weightInKilos; 

- (float)bodyMassIndex 
{ 
    //return weightInKilos/(heightInMeters * heightInMeters); 
    float h = [self heightInMeters]; 
    return [self weightInKilos]/(h * h); 
} 

@end 

Answer 1

error: no visible @interface for 'Employee' declares the selector 'setWeightInKilos'
error: no visible @interface for 'Employee' declares the selector 'setHeightInMeters'
error: no visible @interface for 'Employee' declares the selector 'bodyMassIndex'

不要有這本書，但它似乎對我來說，Employee要繼承Person，不NSObject 。

這將通過繼承給Employee遺漏的屬性/函數。