Object_c使用技巧

1.判断对像是否实现了某方法。

//.h #import <Foundation/Foundation.h> @interface Tester : NSObject { } -(void) test:(NSString*) msg; -(void) notImp; @end //.m #import "Tester.h" @implementation Tester -(void) test:(NSString*) msg { NSLog(@"%@", msg); } @end //main #import <Foundation/Foundation.h> #import "Tester.h" int main (int argc, const char * argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; id tester = [[Tester alloc] init];//注意，这里使用id SEL testSelector = @selector(test:); SEL notImpSelector = @selector(notImp:); if([tester respondsToSelector:testSelector]) { //tester.m中实现了test方法 [tester test:@"invoke test method"]; } if([tester respondsToSelector:notImpSelector]) { //test.m中没有实现此主就去 [tester notImp]; } [pool drain]; return 0; }

2.获取函数指针

Tester.h #import <Foundation/Foundation.h> @interface Tester : NSObject { } -(void) Test:(NSString*) msg; @end Tester.m #import "Tester.h" @implementation Tester -(void) Test:(NSString*) msg { NSLog(@"%@", msg); } @end main.m #import <Foundation/Foundation.h> #import "Tester.h" int main (int argc, const char * argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; id tester = [[Tester alloc] init]; SEL testSelector = @selector(Test:); //构造选择器 IMP testIMP = [tester methodForSelector: testSelector];//获取函数的指针 for(int i=0;i<10;i++) { //int to NSString //直接使用指针调用对像函数 testIMP(tester,testSelector, [NSString stringWithFormat:@"%d",i]); } [pool drain]; return 0; }

3.将函数调用封装成对象

CurrentDate.h #import <Foundation/Foundation.h> @interface CurrentDate : NSObject { } - (NSString *) stringForDate: (NSDate *)date usingFormatter: (NSDateFormatter *)formatter; @end CurrentDate.m #import "CurrentDate.h" @implementation CurrentDate - (NSString *) stringForDate: (NSDate *)date usingFormatter: (NSDateFormatter *)formatter { return [formatter stringFromDate: date]; } @end main.m #import <Foundation/Foundation.h> #import "CurrentDate.h" //参考：http://theocacao.com/document.page/264 int main (int argc, const char * argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; //原始调用 NSDateFormatter * dateFormat = [[NSDateFormatter alloc] initWithDateFormat:@"%b %d %Y" allowNaturalLanguage: NO]; CurrentDate * currentDateClassObject = [[CurrentDate alloc] init]; NSString * currentDate = [currentDateClassObject stringForDate: [NSDate date] usingFormatter: dateFormat]; NSLog(@"currentDate: %@", currentDate); //NSInvocation调用 SEL mySelector = @selector(stringForDate:usingFormatter:); NSMethodSignature * sig = [[currentDateClassObject class] instanceMethodSignatureForSelector: mySelector]; NSInvocation * myInvocation = [NSInvocation invocationWithMethodSignature: sig]; [myInvocation setTarget: currentDateClassObject]; [myInvocation setSelector: mySelector]; NSDate * myDate = [NSDate date]; [myInvocation setArgument: &myDate atIndex: 2]; NSDateFormatter * dateFormatter = [[NSDateFormatter alloc] init]; [dateFormatter setDateStyle: NSDateFormatterMediumStyle]; [myInvocation setArgument: &dateFormatter atIndex: 3]; NSString * result = nil; [myInvocation retainArguments]; [myInvocation invoke]; [myInvocation getReturnValue: &result]; NSLog(@"The result is: %@", result); [pool drain]; return 0; }