IOS开发（58）之在 Block Object 中获取变量

1 前言

通过本次学习，我们就能够理解在 Objective-C 方法和在 Block Objects 中获取变量的区别。 

2 代码实例

main.m

#import <Foundation/Foundation.h>
#import "TestDemo.h"
int main(int argc, const char * argv[])
{

    @autoreleasepool {
        TestDemo *test = [[TestDemo alloc] init];
//        [test log1];
//        [test simpleMethod];
//        [test simpleMethod2];
//        [test simpleMethod3];
//        [test callCorrectBlockObject];
//        [test simpleMethod4];
//        [test log2];
//        [test scopeTest];
        [test scopeTest2];
    }
    return 0;
}

TestDemo.h

#import <Foundation/Foundation.h>

@interface TestDemo : NSObject

@property (nonatomic, strong) NSString *stringProperty;
-(void)log1;
- (void) simpleMethod;
- (void) simpleMethod2;
- (void) simpleMethod3;
- (void) callCorrectBlockObject;
- (void) simpleMethod4;
-(void)log2;
- (void) scopeTest;
-(void) scopeTest2;
@end

TestDemo.m

#import "TestDemo.h"

@implementation TestDemo

@synthesize stringProperty;

void (^independentBlockObject)(void) = ^(void){
    NSInteger localInteger = 10;
    NSLog(@"local integer = %ld", (long)localInteger);
    localInteger = 20;
    NSLog(@"local integer = %ld", (long)localInteger);
};

-(void)log1{
    independentBlockObject();
}
//只读
- (void) simpleMethod{
    NSUInteger outsideVariable = 10;
    NSMutableArray *array = [[NSMutableArray alloc]
                             initWithObjects:@"obj1",
                             @"obj2", nil];
    [array sortUsingComparator:^NSComparisonResult(id obj1, id obj2) {
        NSUInteger insideVariable = 20;
        NSLog(@"Outside variable = %lu", (unsigned long)outsideVariable);
        NSLog(@"Inside variable = %lu", (unsigned long)insideVariable);
        /* Return value for our block object */
        return NSOrderedSame;
    }];
}
//可该
- (void) simpleMethod2{
    __block NSUInteger outsideVariable = 10;
    NSMutableArray *array = [[NSMutableArray alloc]
                             initWithObjects:@"obj1",
                             @"obj2", nil];
    [array sortUsingComparator:^NSComparisonResult(id obj1, id obj2) {
        NSUInteger insideVariable = 20;
        outsideVariable = 30;
        NSLog(@"Outside variable = %lu", (unsigned long)outsideVariable);
        NSLog(@"Inside variable = %lu", (unsigned long)insideVariable);
        /* Return value for our block object */
        return NSOrderedSame;
    }];
}
//获得self
- (void) simpleMethod3{
    NSMutableArray *array = [[NSMutableArray alloc]
                             initWithObjects:@"obj1",
                             @"obj2", nil];
    [array sortUsingComparator:^NSComparisonResult(id obj1, id obj2) {
        NSLog(@"self = %@", self);
        /* Return value for our block object */ return NSOrderedSame;
    }]; }



//无变化Block Object要获得 self需要传参数进去
void (^correctBlockObject)(id) = ^(id self){
    NSLog(@"self = %@", self);
};
- (void) callCorrectBlockObject{
    correctBlockObject(self); }



//修改类属性
- (void) simpleMethod4{
    NSMutableArray *array = [[NSMutableArray alloc]
                             initWithObjects:@"obj1",
                             @"obj2", nil];
    [array sortUsingComparator:^NSComparisonResult(id obj1, id obj2) {
        NSLog(@"self = %@", self);
        self.stringProperty = @"Block Objects";
        NSLog(@"String property = %@", self.stringProperty);
        /* Return value for our block object */
        return NSOrderedSame;
    }];
}

//在独立 Block Object 内部,你不能使用 dot notation 读写一个已声明属性,在这个场景中可以使用这个合成属性的 getter and setter 方法来代替 dot notation:
void (^correctBlockObject1)(id) = ^(id self){ NSLog(@"self = %@", self);
    /* This will work fine */
    [self setStringProperty:@"Block Objects"]; /* This will work fine as well */
    NSLog(@"self.stringProperty = %@",[self stringProperty]);
};

-(void)log2{
    correctBlockObject1(self);
}

//当出现在内联 Block Objects 中,有一条非常重要的规则你必须记住:内联 Block Objects 在其词法区域 会为这些变量复制值。此处发生的事情是在执行 Block 的地方 Block Object 自身一直有一个 integerValue 变量的只读复制。
typedef void (^BlockWithNoParams)(void);
- (void) scopeTest{
    NSUInteger integerValue = 10;
    /*************** Definition of internal block object ***************/
    BlockWithNoParams myBlock = ^{
        NSLog(@"Integer value inside the block = %lu", (unsigned long)integerValue);
    };
    /*************** End definition of internal block object ***************/ integerValue = 20;
    /* Call the block here after changing the
     value of the integerValue variable */
    myBlock();
    NSLog(@"Integer value outside the block = %lu",(unsigned long)integerValue);
}

//可改变变量值测试
-(void) scopeTest2{
    __block NSUInteger integerValue = 10;
    /*************** Definition of internal block object ***************/
    BlockWithNoParams myBlock = ^{
        NSLog(@"Integer value inside the block = %lu", (unsigned long)integerValue);
    };
    /*************** End definition of internal block object ***************/ integerValue = 20;
    /* Call the block here after changing the
     value of the integerValue variable */
    myBlock();
    NSLog(@"Integer value outside the block = %lu",
          (unsigned long)integerValue);
}
@end

运行结果

2013-05-09 22:25:34.087 BlockObjectParamTest[946:303] Integer value inside the block = 20

2013-05-09 22:25:34.089 BlockObjectParamTest[946:303] Integer value outside the block = 20

3 结语

以上就是所有内容，希望对大家有所帮助。

Demo代码下载：http://download.csdn.net/detail/u010013695/5350819