Objective C -- 문법정리 : block

Objective C --  문법정리 : block

참고 : http://stackoverflow.com/a/9201774

         http://rypress.com/tutorials/objective-c/blocks

         http://www.tutorialspoint.com/objective_c/objective_c_blocks.htm

Block  == 다른언어의 무명함수, 람다함수

1. Blocks as Variables

return_type (^blockName)(var_type) = ^return_type (var_type varName)

{

    // ...

};

또는 

return_type (^blockName)(var_type) = ^(var_type varName)

{

    // ...

};

주석 ;  ^return_type (var_type varName) 에서 return_type 은 생략가능 !

예 1.

void (^simpleBlock)(void) = ^{

    NSLog(@"This is a block");

};

simpleBlock();

예 2.

double (^multiplyTwoValues)(double, double) = 

    ^(double firstValue, double secondValue) {

   return firstValue * secondValue;

    };

double result = multiplyTwoValues(2,4);

2. typedef Block

typedef return_type (^blockName)(var_type);

예 .

#import <Foundation/Foundation.h>

typedef void (^CompletionBlock)();

@interface SampleClass:NSObject

- (void)performActionWithCompletion:(CompletionBlock)completionBlock;

@end

@implementation SampleClass

- (void)performActionWithCompletion:(CompletionBlock)completionBlock{

    NSLog(@"Action Performed");

    completionBlock();   // 매개변수로 받은 Block 함수를 실행.

}

@end

int main()

{

    /* my first program in Objective-C */

    SampleClass *sampleClass = [[SampleClass alloc]init];

    [sampleClass performActionWithCompletion:^{

        NSLog(@"Completion is called to intimate action is performed.");

    }];   // 매개변수로 Block 함수 넘김.

    

    return 0;

}

3. Blocks as Properties

@property (copy) return_type (^blockName) (var_type);

4. Blocks as Arguments

[someObject doSomethingWithBlock: ^return_type (var_type varName)

{

    //...

}];

5. method parameter

- (void)someMethodThatTakesABlock:(returnType (^nullability)(parameterTypes))blockName;

예 .

// Car.h

#import <Foundation/Foundation.h>

@interface Car : NSObject

@property double odometer;

- (void)driveForDuration:(double)duration

       withVariableSpeed:(double (^)(double time))speedFunction

                   steps:(int)numSteps;

@end

// Car.m

#import "Car.h"

@implementation Car

@synthesize odometer = _odometer;

- (void)driveForDuration:(double)duration

       withVariableSpeed:(double (^)(double time))speedFunction

                   steps:(int)numSteps {

    double dt = duration / numSteps;

    for (int i=1; i<=numSteps; i++) {

        _odometer += speedFunction(i*dt) * dt;

    }

}

@end

// main.m

#import <Foundation/Foundation.h>

#import "Car.h"

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

    @autoreleasepool {

        Car *theCar = [[Car alloc] init];

        

        // Drive for awhile with constant speed of 5.0 m/s

        [theCar driveForDuration:10.0

               withVariableSpeed:^(double time) {

                           return 5.0;

                       } steps:100];  // 매개변수로 Block 함수 넘김.

        NSLog(@"The car has now driven %.2f meters", theCar.odometer);

        

        // Start accelerating at a rate of 1.0 m/s^2

        [theCar driveForDuration:10.0

               withVariableSpeed:^(double time) {

                           return time + 5.0;

                       } steps:100];  // 매개변수로 Block 함수 넘김.

        NSLog(@"The car has now driven %.2f meters", theCar.odometer);

    }

    return 0;

}

6. Anonymous Block

^return_type (var_type varName)

{

    //...

};

7. Inline Block

^return_type (var_type varName)

{

    //...

}(var);

8. Recursive Blocks

__block return_type (^blockName)(var_type) = [^return_type (var_type varName)

{

    if (returnCondition)

    {

        blockName = nil;

        return;

    }

    // ...

} copy];

blockName(varValue);

9. Returning Blocks

- (return_type(^)(var_type))methodName

{

    // ...

}

as can a function, if a bit strangely.

return_type (^FunctionName())(var_type)

{

    // ...

}