Block在引用不同类型的外部变量的时候，它的位置也是不同的。

先看这样的一段代码：

NSInteger globalVariable = 1;

@interface RXBlockChangeOverTimeObject()
@property (nonatomic, copy) NSInteger(^block)(NSInteger);
@property (nonatomic, assign) NSInteger instanceVariable;
@end

@implementation RXBlockChangeOverTimeObject
- (void)test
{
    // 定义几种类型的变量
    self.instanceVariable = 10;
    NSInteger localVariable = 100;
    static NSInteger staticLocalVariable = 99;
    __block NSInteger blockVariable = 1000;
    // 定义分别使用类型变量的block
    NSInteger (^block_noVariable)(NSInteger) = ^(NSInteger m) {
        return m;
    };
}

几种变量的类型

• 全局变量，例如：globalVariable
• 实例变量，例如：self.instanceVariable
• 本地变量，例如：localVariable
• 本地静态变量，例如：staticLocalVariable
• __block变量，例如：blockVariable
• 入参，例如：NSInteger m

输出block信息：

+ (void)printBlockWithPrefix:(NSString *)prefix block:(id)block
{
    NSLog(@"%@, class:%@, address:%p", prefix, [block class], block);
}

ARC 环境下的测试：

- (void)test
{
    NSLog(@"--------RXBlockChangeOverTimeObject--------");
    // 定义几种类型的变量
    self.instanceVariable = 10;
    NSInteger localVariable = 100;
    static NSInteger staticLocalVariable = 99;
    __block NSInteger blockVariable = 1000;
    
    // 定义分别使用类型变量的block
    NSInteger (^block_noVariable)(NSInteger) = ^(NSInteger m) {
        return m;
    };
    NSInteger (^block_globalVariable)(NSInteger) = ^(NSInteger m) {
        return m + globalVariable;
    };
    __weak typeof(self) weakSelf = self;
    NSInteger (^block_instanceVariable)(NSInteger) = ^(NSInteger m) {
        return m + weakSelf.instanceVariable;
    };
    NSInteger (^block_localVariable)(NSInteger) = ^(NSInteger m) {
        return m + localVariable;
    };
    NSInteger (^block_staticLocalVariable)(NSInteger) = ^(NSInteger m) {
        return m + staticLocalVariable;
    };
    NSInteger (^block_blockVariable)(NSInteger) = ^(NSInteger m) {
        blockVariable++;
        return m + blockVariable;
    };
    NSInteger (^block_composedVarialbe)(NSInteger) = ^(NSInteger m) {
        return m + localVariable + staticLocalVariable;
    };
    
    // 输出定义好的block变量
    [RXPrintUtil printBlockWithPrefix:@"block_noVariable" block:block_noVariable];
    [RXPrintUtil printBlockWithPrefix:@"block_globalVariable" block:block_globalVariable];
    [RXPrintUtil printBlockWithPrefix:@"block_instanceVariable" block:block_instanceVariable];
    [RXPrintUtil printBlockWithPrefix:@"block_localVariable" block:block_localVariable];
    [RXPrintUtil printBlockWithPrefix:@"block_staticLocalVariable" block:block_staticLocalVariable];
    [RXPrintUtil printBlockWithPrefix:@"block_blockVariable" block:block_blockVariable];
    [RXPrintUtil printBlockWithPrefix:@"block_composedVarialbe" block:block_composedVarialbe];
    
    // 分别设置block
    self.block = block_noVariable;
    [RXPrintUtil printBlockWithPrefix:@"self block_noVariable" block:self.block];
    
    self.block = block_globalVariable;
    [RXPrintUtil printBlockWithPrefix:@"self block_globalVariable" block:self.block];
    
    self.block = block_instanceVariable;
    [RXPrintUtil printBlockWithPrefix:@"self block_instanceVariable" block:self.block];
    
    self.block = block_localVariable;
    [RXPrintUtil printBlockWithPrefix:@"self block_localVariable" block:self.block];
    
    self.block = block_staticLocalVariable;
    [RXPrintUtil printBlockWithPrefix:@"self block_staticLocalVariable" block:self.block];
    
    self.block = block_blockVariable;
    [RXPrintUtil printBlockWithPrefix:@"self block_blockVariable" block:self.block];
    
    self.block = block_composedVarialbe;
    [RXPrintUtil printBlockWithPrefix:@"self block_composedVarialbe" block:self.block];
}

运行结果：

--------RXBlockChangeOverTimeObject--------
block_noVariable, class:__NSGlobalBlock__, address:0x10753ad40
block_globalVariable, class:__NSGlobalBlock__, address:0x10753ad80
block_instanceVariable, class:__NSMallocBlock__, address:0x60000024fc60
block_localVariable, class:__NSMallocBlock__, address:0x6000002502c0
block_staticLocalVariable, class:__NSGlobalBlock__, address:0x10753ae10
block_blockVariable, class:__NSMallocBlock__, address:0x600000250740
block_composedVarialbe, class:__NSMallocBlock__, address:0x600000253680
self block_noVariable, class:__NSGlobalBlock__, address:0x10753ad40
self block_globalVariable, class:__NSGlobalBlock__, address:0x10753ad80
self block_instanceVariable, class:__NSMallocBlock__, address:0x60000024fc60
self block_localVariable, class:__NSMallocBlock__, address:0x6000002502c0
self block_staticLocalVariable, class:__NSGlobalBlock__, address:0x10753ae10
self block_blockVariable, class:__NSMallocBlock__, address:0x600000250740
self block_composedVarialbe, class:__NSMallocBlock__, address:0x600000253680
RXBlockChangeOverTimeMRCObject dealloc

MRC环境下的测试：

#include <malloc/malloc.h>
- (void)test
{
    NSLog(@"--------RXBlockChangeOverTimeMRCObject--------");
    // 这一部分的测试代码就跟ARC测试代码一致，只不过如下的不一样：
    // MRC解决循环引用
    __block __typeof(self) weakSelf = self;
    NSInteger (^block_instanceVariable)(NSInteger) = ^(NSInteger m) {
        if (malloc_zone_from_ptr(weakSelf)) {
            return m + weakSelf.instanceVariable;
        } else {
            return m;
        }
    };
}
- (void)dealloc
{
    [super dealloc];
    NSLog(@"RXBlockChangeOverTimeMRCObject dealloc");
}

运行结果：

--------RXBlockChangeOverTimeMRCObject--------
block_noVariable, class:__NSGlobalBlock__, address:0x107537ac0
block_globalVariable, class:__NSGlobalBlock__, address:0x107537b00
block_instanceVariable, class:__NSStackBlock__, address:0x7ffee8c656e8
block_localVariable, class:__NSStackBlock__, address:0x7ffee8c656b8
block_staticLocalVariable, class:__NSGlobalBlock__, address:0x107537b90
block_blockVariable, class:__NSStackBlock__, address:0x7ffee8c65680
block_composedVarialbe, class:__NSStackBlock__, address:0x7ffee4dc4650
self block_noVariable, class:__NSGlobalBlock__, address:0x107537ac0
self block_globalVariable, class:__NSGlobalBlock__, address:0x107537b00
self block_instanceVariable, class:__NSMallocBlock__, address:0x600000253680
self block_localVariable, class:__NSMallocBlock__, address:0x6000002502c0
self block_staticLocalVariable, class:__NSGlobalBlock__, address:0x107537b90
self block_blockVariable, class:__NSMallocBlock__, address:0x6000002502c0
self block_composedVarialbe, class:__NSMallocBlock__, address:0x60400025e900
RXBlockChangeOverTimeMRCObject dealloc

1. 可以把RXBlockChangeOverTimeMRCObject.m文件的compiler flsgs设置为：fno-objc-arc来表明此文件是MRC的。
2. 也可以在MRC下使用__weak：
   image.png
   默认是No，可以改成Yes

结论

image.png