ios學習筆記之block在ios開發中的應用,ios學習筆記
一、什麼是Blocks Block是一個C層級的文法以及運行時的一個特性,和標準C中的函數(函數指標)類似,但是其運行需要編譯器和運行時支援,從ios4.0開始就很好的支援Block。
二、在ios開發中,什麼情況下使用Block Block除了能夠定義參數列表、傳回型別外,還能夠擷取被定義時的詞法範圍內的狀態(比如局部變數),並且在一定條件下(比如使用__block變數)能夠修改這些狀態。此外,這些可修改的狀態在相同詞法範圍內的多個block之間是共用的,即便出了該詞法範圍(比如棧展開,出了範圍),仍可以繼續共用或者修改這些狀態。通常來說,block都是一些簡短程式碼片段的封裝,適用作工作單元,通常用來做並發任務、遍曆、以及回調。
三、block如何申明(對比於c語言中的函數申明) 四、c函數指正和blocks調用 int (*CFunc) (int a) 函數調用 int result = CFunc(10); int (^BFunc) (int a) 函數調用 int result = BFunc(10);
五、__block 關鍵字 一個Block的內部時可以引用自身範圍外的變數的,包括static變數,extern變數或自由變數(定義一個變數的時候,如果不加儲存修飾符,預設情況下就是自由變數auto,auto變數儲存在stack中的。除了auto之外還存在register,static等儲存修飾符),對於自由變數,在Block中唯讀。在引入block的同時,還引入了一種特殊的__block關鍵字變數儲存修飾符。
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);}
列印結果如下 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變數
void (^BarkCallback) (Dog *thisDog, int count);
}
@property (assign) int ID;
//向外暴露一個介面
-(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變數 void (^BarkCallback) (Dog *thisDog, int count);}@property (assign) int ID;//向外暴露一個介面-(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對象進行彙報
if (BarkCallback) {
//調用從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對象進行彙報 if (BarkCallback) { //調用從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、列印結果 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