iOS Block 探索

Block：带有自动变量的匿名函数。

匿名函数：没有函数名的函数，一对{}包裹的内容是匿名函数的作用域。

自动变量：栈上声明的一个变量不是静态变量和全局变量，是不可以在这个栈内声明的匿名函数中使用的，但在Block中却可以。

准备Demo

#import "ViewController.h"

void (^block_global)(void) = ^ {
    NSLog(@"block_global");
};

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    void (^block0)(void) = ^ {
        NSLog(@"block0");
    };
    
    BOOL (^block1)(NSString *string) = ^(NSString *string) {
        NSLog(@"%@", string);
        return NO;
    };
    
    int a = 0;
    NSString *b = @"hello";
    NSArray *c = @[@"hello", @"world"];
    NSMutableArray *d = c.mutableCopy;
    
    __block double e = 1.0f;
    __block NSMutableDictionary *dic = [NSMutableDictionary dictionaryWithObjectsAndKeys:@"dictionary", @"key", nil];
    
    BOOL (^block2)(NSNumber *number) = ^(NSNumber *number) {
        NSLog(@"block%d\n%d %@ %@ %@ %f %@", number.intValue, a, b, c, d, e, dic);
        return YES;
    };
    
    block0();
    block1(@"block1");
    block2(@2);
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

将ViewController.m编译成C++，以便研究，脚本命令如下：

1	clang -x objective-c -rewrite-objc -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk ViewController.m

下面来逐一进行分析