ios學(xué)習(xí)筆記之block在ios開發(fā)中的應(yīng)用

2019-11-14 19:17:19

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一、什么是Blocks      Block是一個C級別的語法以及運行時的一個特性，和標準C中的函數(shù)（函數(shù)指針）類似，但是其運行需要編譯器和運行時支持，從ios4.0開始就很好的支持Block。
二、在ios開發(fā)中，什么情況下使用Block      Block除了能夠定義參數(shù)列表、返回類型外，還能夠獲取被定義時的詞法范圍內(nèi)的狀態(tài)（比如局部變量），并且在一定條件下（比如使用__block變量）能夠修改這些狀態(tài)。此外，這些可修改的狀態(tài)在相同詞法范圍內(nèi)的多個block之間是共享的，即便出了該詞法范圍（比如棧展開，出了作用域），仍可以繼續(xù)共享或者修改這些狀態(tài)。通常來說，block都是一些簡短代碼片段的封裝，適用作工作單元，通常用來做并發(fā)任務(wù)、遍歷、以及回調(diào)。
三、block如何申明（對比于c語言中的函數(shù)申明） 四、c函數(shù)指正和blocks調(diào)用      int (*CFunc) (int a) 函數(shù)調(diào)用      int result = CFunc(10);      int (^BFunc) (int a) 函數(shù)調(diào)用      int result = BFunc(10);
五、__block 關(guān)鍵字      一個Block的內(nèi)部時可以引用自身作用域外的變量的，包括static變量，extern變量或自由變量（定義一個變量的時候，如果不加存儲修飾符，默認情況下就是自由變量auto，auto變量保存在stack中的。除了auto之外還存在register，static等存儲修飾符），對于自由變量，在Block中只讀的。在引入block的同時，還引入了一種特殊的__block關(guān)鍵字變量存儲修飾符。
六、block的幾個小例子

java代碼

#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);
//此處如果不加__block會報錯
__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);
}

#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);                //此處如果不加__block會報錯        __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);}

打印結(jié)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寫的回調(diào)例子 1、Dog.h

Java代碼

#import <Foundation/Foundation.h>
@interface Dog : NSObject {
int _ID;
NSTimer *timer;
int barkCount;
//定義一個blocks變量
void (^BarkCallback) (Dog *thisDog, int count);
}
@PRoperty (assign) int ID;
//向外暴露一個接口
-(void) setBark:( void (^) (Dog *thisDog, int count) ) eachBark;
@end

#import <Foundation/Foundation.h>@interface Dog : NSObject {    int _ID;    NSTimer *timer;    int barkCount;        //定義一個blocks變量    void (^BarkCallback) (Dog *thisDog, int count);}@property (assign) int ID;//向外暴露一個接口-(void) setBark:( void (^) (Dog *thisDog, int count) ) eachBark;@end

2、Dog.m

Java代碼

#import "Dog.h"
@implementation Dog
@synthesize ID = _ID;
-(id) init
{
self = [superinit];
if (self) {
//每隔1s調(diào)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對象進行匯報
if (BarkCallback) {
//調(diào)用從Person傳過來的Blocks
BarkCallback(self, barkCount);
}
}
-(void) setBark:(void (^)(Dog *, int))eachBark
{
[BarkCallbackrelease];
BarkCallback = [eachBark copy];
}
-(void) dealloc
{
[BarkCallbackrelease];
[superdealloc];
}
@end

#import "Dog.h"@implementation Dog@synthesize ID = _ID;-(id) init{    self = [superinit];    if (self) {        //每隔1s調(diào)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對象進行匯報    if (BarkCallback) {        //調(diào)用從Person傳過來的Blocks        BarkCallback(self, barkCount);    }}-(void) setBark:(void (^)(Dog *, int))eachBark{    [BarkCallbackrelease];    BarkCallback = [eachBark copy];}-(void) dealloc{    [BarkCallbackrelease];    [superdealloc];}@end

3、Person.h

Java代碼

#import <Foundation/Foundation.h>
#import "Dog.h"
@interface Person : NSObject
{
Dog *_dog;
}
@property (retain) Dog *dog;
@end

#import <Foundation/Foundation.h>#import "Dog.h"@interface Person : NSObject{    Dog *_dog;}@property (retain) Dog *dog;@end

4、Person.m

Java代碼

#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

#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代碼

#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;
}

#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、打印結(jié)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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