ios学习笔记之block在ios开发中的应用

ios学习笔记之block在ios开发中的应用
一、什么是Blocks      Block是一个C级别的语法以及运行时的一个特性，和标准C中的函数（函数指针）类似，但是其运行需要编译器和运行时支持，从ios4.0开始就很好的支持Block。
二、在ios开发中，什么情况下使用Block      Block除了能够定义参数列表、返回类型外，还能够获取被定义时的词法范围内的状态（比如局部变量），并且在一定条件下（比如使用__block变量）能够修改这些状态。此外，这些可修改的状态在相同词法范围内的多个block之间是共享的，即便出了该词法范围（比如栈展开，出了作用域），仍可以继续共享或者修改这些状态。通常来说，block都是一些简短代码片段的封装，适用作工作单元，通常用来做并发任务、遍历、以及回调。
三、block如何申明（对比于c语言中的函数申明） 四、c函数指正和blocks调用      int (*CFunc) (int a) 函数调用      int result = CFunc(10);      int (^BFunc) (int a) 函数调用      int result = BFunc(10);
五、__block 关键字      一个Block的内部时可以引用自身作用域外的变量的，包括static变量，extern变量或自由变量（定义一个变量的时候，如果不加存储修饰符，默认情况下就是自由变量auto，auto变量保存在stack中的。除了auto之外还存在register，static等存储修饰符），对于自由变量，在Block中只读的。在引入block的同时，还引入了一种特殊的__block关键字变量存储修饰符。
六、block的几个小例子
Java代码
1. #import <Cocoa/Cocoa.h>
4. int main(int argc, char *argv[])
5. {
6. @autoreleasepool {
7. NSLog(@"Hello world");
8. void (^myblocks) (void) = NULL;
9. myblocks = ^(void) {
10. NSLog(@"in blocks");
11. };
12. NSLog(@"before myblocks");
13. myblocks();
14. NSLog(@"after myblocks");
17. int (^myblocks2) (int a, int b) = ^(int a, int b) {
18. int c = a + b;
19. return c;
20. };
21. NSLog(@"before blocks2");
22. int ret = myblocks2(10, 20);
23. NSLog(@"after blocks2 ret %d", ret);
25. //此处如果不加__block会报错
26. __blockint sum = 0;
27. int (^myblocks3) (int a, int b) = ^(int a, int b) {
28. sum = a + b;
29. return3;
30. };
31. myblocks3(20, 30);
32. NSLog(@"sum is %d", sum);
33. }
34. returnNSApplicationMain(argc, (constchar **)argv);
35. }
```
#import <Cocoa/Cocoa.h>


int main(int argc, char *argv[])
{
    @autoreleasepool {
        NSLog(@"Hello world");
        void (^myblocks) (void) = NULL;
        myblocks = ^(void) {
            NSLog(@"in blocks");
        };
        NSLog(@"before myblocks");
        myblocks();
        NSLog(@"after myblocks");
        
        
        int (^myblocks2) (int a, int b) = ^(int a, int b) {
            int c = a + b;
            return c;
        };
        NSLog(@"before blocks2");
        int ret = myblocks2(10, 20);
        NSLog(@"after blocks2 ret %d", ret);
        
        //此处如果不加__block会报错
        __blockint sum = 0;
        int (^myblocks3) (int a, int b) = ^(int a, int b) {
            sum = a + b;
            return3;
        };
        myblocks3(20, 30);
        NSLog(@"sum is %d", sum);
    }
    returnNSApplicationMain(argc, (constchar **)argv);
}
```
打印结果如下 2012-09-03 10:23:20.878 blockTest[407:403] Hello world 2012-09-03 10:23:20.880 blockTest[407:403] before myblocks 2012-09-03 10:23:20.881 blockTest[407:403] in blocks 2012-09-03 10:23:20.881 blockTest[407:403] after myblocks 2012-09-03 10:23:20.882 blockTest[407:403] before blocks2 2012-09-03 10:23:20.882 blockTest[407:403] after blocks2 ret 30 2012-09-03 10:23:20.882 blockTest[407:403] sum is 50
七、block写的回调例子 1、Dog.h
Java代码
1. #import <Foundation/Foundation.h>
4. @interface Dog : NSObject {
5. int _ID;
6. NSTimer *timer;
7. int barkCount;
9. //定义一个blocks变量
10. void (^BarkCallback) (Dog *thisDog, int count);
11. }
12. @property (assign) int ID;
15. //向外暴露一个接口
16. -(void) setBark:( void (^) (Dog *thisDog, int count) ) eachBark;
19. @end
```
#import <Foundation/Foundation.h>


@interface Dog : NSObject {
    int _ID;
    NSTimer *timer;
    int barkCount;
    
    //定义一个blocks变量
    void (^BarkCallback) (Dog *thisDog, int count);
}
@property (assign) int ID;


//向外暴露一个接口
-(void) setBark:( void (^) (Dog *thisDog, int count) ) eachBark;


@end
```
2、Dog.m
Java代码
1. #import "Dog.h"
4. @implementation Dog
5. @synthesize ID = _ID;
8. -(id) init
9. {
10. self = [superinit];
11. if (self) {
12. //每隔1s调用一次updateTimer方法
13. timer = [NSTimerscheduledTimerWithTimeInterval:1.0ftarget:selfselector:@selector(updateTimer:) userInfo:nilrepeats:YES];
15. }
16. returnself;
17. }
20. -(void) updateTimer:(id) arg
21. {
22. barkCount ++;
23. NSLog(@"dog %d bark count %d", _ID, barkCount);
24. //向Person对象进行汇报
25. if (BarkCallback) {
26. //调用从Person传过来的Blocks
27. BarkCallback(self, barkCount);
28. }
29. }
34. -(void) setBark:(void (^)(Dog *, int))eachBark
35. {
36. [BarkCallbackrelease];
37. BarkCallback = [eachBark copy];
38. }
41. -(void) dealloc
42. {
43. [BarkCallbackrelease];
44. [superdealloc];
45. }
46. @end
```
#import "Dog.h"


@implementation Dog
@synthesize ID = _ID;


-(id) init
{
    self = [superinit];
    if (self) {
        //每隔1s调用一次updateTimer方法
        timer = [NSTimerscheduledTimerWithTimeInterval:1.0ftarget:selfselector:@selector(updateTimer:) userInfo:nilrepeats:YES];
        
    }
    returnself;
}


-(void) updateTimer:(id) arg
{
    barkCount ++;
    NSLog(@"dog %d bark count %d", _ID, barkCount);
    //向Person对象进行汇报
    if (BarkCallback) {
        //调用从Person传过来的Blocks
        BarkCallback(self, barkCount);
    }
}




-(void) setBark:(void (^)(Dog *, int))eachBark
{
    [BarkCallbackrelease];
    BarkCallback = [eachBark copy];
}


-(void) dealloc
{
    [BarkCallbackrelease];
    [superdealloc];
}
@end
```
3、Person.h
Java代码
1. #import <Foundation/Foundation.h>
2. #import "Dog.h"
5. @interface Person : NSObject
6. {
7. Dog *_dog;
8. }
11. @property (retain) Dog *dog;
14. @end
```
#import <Foundation/Foundation.h>
#import "Dog.h"


@interface Person : NSObject
{
    Dog *_dog;
}


@property (retain) Dog *dog;


@end
```
4、Person.m
Java代码
1. #import "Person.h"
4. @implementation Person
5. @synthesize dog = _dog;
8. -(void) setDog:(Dog *)dog
9. {
10. if (_dog != dog) {
11. [_dogrelease];
12. _dog = [dog retain];
14. [_dogsetBark:^(Dog *thisDog, int count) {
15. NSLog(@"person dog %d count %d", [thisDog ID], count);
16. }];
17. }
18. }
21. -(Dog *) dog
22. {
23. return_dog;
24. }
27. -(void) dealloc
28. {
29. self.dog = nil;
30. [superdealloc];
31. }
34. @end
```
#import "Person.h"


@implementation Person
@synthesize dog = _dog;


-(void) setDog:(Dog *)dog
{
    if (_dog != dog) {
        [_dogrelease];
        _dog = [dog retain];
        
        [_dogsetBark:^(Dog *thisDog, int count) {
            NSLog(@"person dog %d count %d", [thisDog ID], count);
        }];
    }
}


-(Dog *) dog
{
    return_dog;
}


-(void) dealloc
{
    self.dog = nil;
    [superdealloc];
}


@end
```
5、Main.m
Java代码
1. #import <Foundation/Foundation.h>
2. #import "Person.h"
3. #import "Dog.h"
6. int main(int argc, constchar * argv[])
7. {
10. @autoreleasepool {
12. // insert code here...
13. NSLog(@"Hello, World!");
14. Person *person = [[Personalloc] init];
15. Dog *dog = [[Dogalloc] init];
16. [dog setID:10];
17. [person setDog:dog];
18. [dog release];
19. while (1) {
20. [[NSRunLoopcurrentRunLoop] run];
21. }
22. [person release];
24. }
25. return 0;
26. }
```
#import <Foundation/Foundation.h>
#import "Person.h"
#import "Dog.h"


int main(int argc, constchar * argv[])
{


    @autoreleasepool {
        
        // insert code here...
        NSLog(@"Hello, World!");
        Person *person = [[Personalloc] init];
        Dog *dog = [[Dogalloc] init];
        [dog setID:10];
        [person setDog:dog];
        [dog release];
        while (1) {
            [[NSRunLoopcurrentRunLoop] run];
        }
        [person release];
        
    }
    return 0;
}
```
6、打印结果 2012-09-03 11:21:08.551 blockDelegate[549:403] Hello, World! 2012-09-03 11:21:09.554 blockDelegate[549:403] dog 10 bark count 1 2012-09-03 11:21:09.555 blockDelegate[549:403] person dog 10 count 1 2012-09-03 11:21:10.554 blockDelegate[549:403] dog 10 bark count 2 2012-09-03 11:21:10.555 blockDelegate[549:403] person dog 10 count 2 2012-09-03 11:21:11.553 blockDelegate[549:403] dog 10 bark count 3 2012-09-03 11:21:11.554 blockDelegate[549:403] person dog 10 count 3 2012-09-03 11:21:12.554 blockDelegate[549:403] dog 10 bark count 4 2012-09-03 11:21:12.555 blockDelegate[549:403] person dog 10 count 4 2012-09-03 11:21:13.553 blockDelegate[549:403] dog 10 bark count 5 2012-09-03 11:21:13.553 blockDelegate[549:403] person dog 10 count 5 2012-09-03 11:21:14.553 blockDelegate[549:403] dog 10 bark count 6 2012-09-03 11:21:14.554 blockDelegate[549:403] person dog 10 count 6
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原文地址：https://www.cnblogs.com/lovewx/p/4202715.html