Object-c Block分析

本文是来自一位大神的分析博客，俺找不到他的博客地址了：
代码记录下来当作 自己的笔记吧

//
//  main.m
//  BlockDemo
//
//  Created by liuxiaobing on 2018/7/25.
//  Copyright © 2018 liuxiaobing. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "MyClass.h"
#import "ARCBlockTest.h"


NSString *__globalString = nil;

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        // insert code here...
        NSLog(@"Hello, World!");
//        MyClass* obj = [[[MyClass alloc] init] autorelease];
//        [obj test];



        /**-------------------------以下测试例子请在 arc环境下进行--------------------*/
        //测试testGlobalObj
//        __globalString = @"1";
//        void (^TestBlock)(void) = ^{
//
//            NSLog(@"string is :%@", __globalString); //string is :( null)
//        };
//
//        __globalString = nil;
//        TestBlock();
        /**-------------------------end--------------------*/

        //测试静态变量
//        static NSString *__staticString = nil;
//        __staticString = @"1";
//
//        printf("38----------static address: %p\n", &__staticString);    //static address: 0x6a8c
//
//        void (^TestStaticBlock)(void) = ^{
//
//            printf("42---------static address: %p\n", &__staticString); //static address: 0x6a8c  两者地址一致，所以当访问静态变量时，未拷贝对象指针
//
//            NSLog(@"44--------string is : %@", __staticString); //string is :( null)
//        };
//        __staticString = nil;
//        TestStaticBlock();
        /**-------------------------end--------------------*/


        //测试局部变量------使用local变量时，block会复制指针，且强引用指针指向的对象一次
        //局部自动变量，在Block中只读。Block定义时copy变量的值，在Block中作为常量使用，所以即使变量的值在Block外改变，也不影响他在Block中的值。
        NSString *__localString = nil;
        __localString = @"1";

        printf("local address: %p\n", &__localString); //local address: 0xbfffd9c0
        ARCBlockTest *testBlock = [[ARCBlockTest alloc] init];
        testBlock.test = @"64";

        void (^TestBlock)(void) = ^{

            printf("local address: %p\n", &__localString); //local address: 0x71723e4   两者地址不一样，说明指向对象的指针被拷贝了
            NSLog(@"62---------localString is : %@", __localString); //string is : 1
            NSLog(@"67--------在block 中引用局部对象，不会造成内存泄露：%@",testBlock.test);
        };

        __localString = nil;
        TestBlock();
        NSLog(@"72-------------:%@",TestBlock);


    }
    return 0;
}







//- (void)testGlobalObj
//{
//    __globalString = @"1";
//    void (^TestBlock)(void) = ^{
//
//        NSLog(@"string is :%@", __globalString); //string is :( null)
//    };
//
//    __globalString = nil;
//
//    TestBlock();
//}

//- (void)testStaticObj
//{
//    static NSString *__staticString = nil;
//    __staticString = @"1";
//
//    printf("static address: %p\n", &__staticString);    //static address: 0x6a8c
//
//    void (^TestBlock)(void) = ^{
//
//        printf("static address: %p\n", &__staticString); //static address: 0x6a8c
//
//        NSLog(@"string is : %@", __staticString); //string is :( null)
//    };
//
//    __staticString = nil;
//
//    TestBlock();
//}
//
//- (void)testLocalObj
//{
//    NSString *__localString = nil;
//    __localString = @"1";
//
//    printf("local address: %p\n", &__localString); //local address: 0xbfffd9c0
//
//    void (^TestBlock)(void) = ^{
//
//        printf("local address: %p\n", &__localString); //local address: 0x71723e4
//
//        NSLog(@"string is : %@", __localString); //string is : 1
//    };
//
//    __localString = nil;
//
//    TestBlock();
//}
//
//- (void)testBlockObj
//{
//    __block NSString *_blockString = @"1";
//
//    void (^TestBlock)(void) = ^{
//
//        NSLog(@"string is : %@", _blockString); // string is :( null)
//    };
//
//    _blockString = nil;
//
//    TestBlock();
//}
//
//- (void)testWeakObj
//{
//    NSString *__localString = @"1";
//
//    __weak NSString *weakString = __localString;
//
//    printf("weak address: %p\n", &weakString);  //weak address: 0xbfffd9c4
//    printf("weak str address: %p\n", weakString); //weak str address: 0x684c
//
//    void (^TestBlock)(void) = ^{
//
//        printf("weak address: %p\n", &weakString); //weak address: 0x7144324
//        printf("weak str address: %p\n", weakString); //weak str address: 0x684c
//
//        NSLog(@"string is : %@", weakString); //string is :1
//    };
//
//    __localString = nil;
//
//    TestBlock();
//}