這三種程式設計方式從上到下,抽象度層次是從低到高的,抽象度越高的使用越簡單,也是Apple最推薦使用的。
這篇我們主要介紹和使用NSThread,後面會繼續2、3 的講解和使用。
NSThread:
優點:NSThread 比其他兩個輕量級
缺點:需要自己管理線程的生命周期,線程同步。線程同步對資料的加鎖會有一定的系統開銷
NSThread實作的技術有下面三種:
Technology
Description
Cocoa threads
POSIX threads
Multiprocessing Services
Multiprocessing Services is a legacy C-based interface used by applications transitioning from older versions of Mac OS. This technology is available in OS X only and should be avoided for any new development. Instead, you should use the <code>NSThread</code> class or POSIX threads. If you need more information on this technology, see Multiprocessing Services Programming Guide.
一般使用cocoa thread 技術。
Cocoa operation
優點:不需要關心線程管理,資料同步的事情,可以把精力放在自己需要執行的操作上。
Cocoa operation 相關的類是 NSOperation ,NSOperationQueue。NSOperation是個抽象類,使用它必須用它的子類,可以實作它或者使用它定義好的兩個子類:NSInvocationOperation 和 NSBlockOperation。建立NSOperation子類的對象,把對象添加到NSOperationQueue隊列裡執行。
GCD
介紹完這三種多線程程式設計方式,我們這篇先介紹NSThread的使用。
- (id)initWithTarget:(id)target selector:(SEL)selector object:(id)argument
+ (void)detachNewThreadSelector:(SEL)aSelector toTarget:(id)aTarget withObject:(id)anArgument
第一個是執行個體方法,第二個是類方法
1、[NSThread detachNewThreadSelector:@selector(doSomething:) toTarget:self withObject:nil];
2、NSThread* myThread = [[NSThread alloc] initWithTarget:self
selector:@selector(doSomething:)
object:nil];
[myThread start];
selector :線程執行的方法,這個selector隻能有一個參數,而且不能有傳回值。
target :selector消息發送的對象
argument:傳輸給target的唯一參數,也可以是nil
第一種方式會直接建立線程并且開始運作線程,第二種方式是先建立線程對象,然後再運作線程操作,在運作線程操作前可以設定線程的優先級等線程資訊
用NSObject的類方法 performSelectorInBackground:withObject: 建立一個線程:
[Obj performSelectorInBackground:@selector(doSomething) withObject:nil];
建立項目,并在xib檔案上放置一個imageView控件。按住control鍵拖到viewControll
er.h檔案中建立imageView IBOutlet
ViewController.m中實作:
//
// ViewController.m
// NSThreadDemo
// Created by rongfzh on 12-9-23.
// Copyright (c) 2012年 rongfzh. All rights reserved.
#import "ViewController.h"
#define kURL @"http://avatar.csdn.net/2/C/D/1_totogo2010.jpg"
@interface ViewController ()
@end
@implementation ViewController
-(void)downloadImage:(NSString *) url{
NSData *data = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:url]];
UIImage *image = [[UIImage alloc]initWithData:data];
if(image == nil){
}else{
[self performSelectorOnMainThread:@selector(updateUI:) withObject:image waitUntilDone:YES];
}
}
-(void)updateUI:(UIImage*) image{
self.imageView.image = image;
- (void)viewDidLoad
{
[super viewDidLoad];
// [NSThread detachNewThreadSelector:@selector(downloadImage:) toTarget:self withObject:kURL];
NSThread *thread = [[NSThread alloc]initWithTarget:self selector:@selector(downloadImage:) object:kURL];
[thread start];
- (void)didReceiveMemoryWarning
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
線程下載下傳完圖檔後怎麼通知主線程更新界面呢?
[self performSelectorOnMainThread:@selector(updateUI:) withObject:image waitUntilDone:YES];
performSelectorOnMainThread是NSObject的方法,除了可以更新主線程的資料外,還可以更新其他線程的比如:
用:performSelector:onThread:withObject:waitUntilDone:
運作下載下傳圖檔:
圖檔下載下傳下來了。
我們示範一個經典的賣票的例子來講NSThread的線程同步:
.h
#import <UIKit/UIKit.h>
@class ViewController;
@interface AppDelegate : UIResponder <UIApplicationDelegate>
int tickets;
int count;
NSThread* ticketsThreadone;
NSThread* ticketsThreadtwo;
NSCondition* ticketsCondition;
NSLock *theLock;
@property (strong, nonatomic) UIWindow *window;
@property (strong, nonatomic) ViewController *viewController;
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
tickets = 100;
count = 0;
theLock = [[NSLock alloc] init];
// 鎖對象
ticketsCondition = [[NSCondition alloc] init];
ticketsThreadone = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];
[ticketsThreadone setName:@"Thread-1"];
[ticketsThreadone start];
ticketsThreadtwo = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];
[ticketsThreadtwo setName:@"Thread-2"];
[ticketsThreadtwo start];
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
// Override point for customization after application launch.
self.viewController = [[ViewController alloc] initWithNibName:@"ViewController" bundle:nil];
self.window.rootViewController = self.viewController;
[self.window makeKeyAndVisible];
return YES;
- (void)run{
while (TRUE) {
// 上鎖
// [ticketsCondition lock];
[theLock lock];
if(tickets >= 0){
[NSThread sleepForTimeInterval:0.09];
count = 100 - tickets;
NSLog(@"目前票數是:%d,售出:%d,線程名:%@",tickets,count,[[NSThread currentThread] name]);
tickets--;
}else{
break;
}
[theLock unlock];
// [ticketsCondition unlock];
如果沒有線程同步的lock,賣票數可能是-1.加上lock之後線程同步保證了資料的正确性。
上面例子我使用了兩種鎖,一種NSCondition ,一種是:NSLock。 NSCondition我已經注釋了。
他們都可以通過
[ticketsCondition signal]; 發送信号的方式,在一個線程喚醒另外一個線程的等待。
比如:
#import "AppDelegate.h"
@implementation AppDelegate
NSThread *ticketsThreadthree = [[NSThread alloc] initWithTarget:self selector:@selector(run3) object:nil];
[ticketsThreadthree setName:@"Thread-3"];
[ticketsThreadthree start];
-(void)run3{
while (YES) {
[ticketsCondition lock];
[NSThread sleepForTimeInterval:3];
[ticketsCondition signal];
[ticketsCondition unlock];
[ticketsCondition wait];
wait是等待,我加了一個 線程3 去喚醒其他兩個線程鎖中的wait
我們可以使用指令 @synchronized 來簡化 NSLock的使用,這樣我們就不必顯示編寫建立NSLock,加鎖并解鎖相關代碼。
- (void)doSomeThing:(id)anObj
{
@synchronized(anObj)
{
// Everything between the braces is protected by the @synchronized directive.
}
}
還有其他的一些鎖對象,比如:循環鎖NSRecursiveLock,條件鎖NSConditionLock,分布式鎖NSDistributedLock等等,可以自己看官方文檔學習
本文轉自 卓行天下 51CTO部落格,原文連結:http://blog.51cto.com/9951038/1772539,如需轉載請自行聯系原作者