iOS 多线程技术1

iOS 多线程技术1

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iOS 有三种多线程编程技术:

• NSThread
• NSOperation
• GCD

它们的抽象程度由低到高,越高的使用起来越简单.

NSThread

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显示调用 NSthread 类

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• 类方法

+ (void)detachNewThreadSelector:(SEL)selector toTarget:(id)target withObject:(id)argument;

• 实例方法

- (instancetype)initWithTarget:(id)target selector:(SEL)selector object:(id)argument [thread start]

隐式调用

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• 开启后台线程

- (void)performSelectorInBackground:(SEL)aSelector withObject:(id)arg

• 在主线程中运行

- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait

• 在指定的线程中执行,但是该线程必须具备 run loop

- (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(id)arg waitUntilDone:(BOOL)wait

常见NSThread 的方法

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+ (NSThread *)currentThread; //获得当前线程+ (void)sleepForTimeInterval:(NSTimeInterval)ti; //线程休眠+ (NSThread *)mainThread; //主线程,即 UI线程+ (BOOL)isMainThread; //判断是否主线程- (BOOL)isMainThread; //同上- (BOOL)isExecuting; // 线程是否正在运行- (BOOL)isFinished; // 线程是否已结束

Demo:
创建一个 lable, 实现程序运行起来一段时间后就能显示一些内容,并且有一个 button 的按钮,当点击时,模拟从网络上刷新出一张图片,从中我们要了解到当需要更新 UI 时,必须在主线程中进行.从用户的角度来说,我看一张图片,不能影响的我在界面的其他操作,否则,这个 app 用着体验太差,我可能会删掉不再使用.

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@interface ViewController ()@property (weak, nonatomic) IBOutlet UIImageView *imageView;@property (weak, nonatomic) IBOutlet UILabel *lable;@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];    // 1.类方法    [NSThread detachNewThreadSelector:@selector(dosomething:) toTarget:self withObject:@"detachNewThreadSelector"];}- (void)dosomething:(NSString * )string{    // 休眠5秒钟,只是模拟一个耗时的操作,如果操作耗时,就另起一个线程执行    [NSThread sleepForTimeInterval:5];    //更新 UI, 必须在主线程中进行  //NO 异步  YES 同步    [self performSelectorOnMainThread:@selector(updateLable:) withObject:string waitUntilDone:NO];    NSLog(@"%s",__func__);}- (void)updateLable:(NSString*)string{    _lable.text = string;}#pragma mark - image view- (IBAction)btnAction:(UIButton *)sender {    //实例方法    NSString *urlStr =  @"http://img.hb.aicdn.com/5a8f57157b47284724d09ffd2da28369731f8144ac9c-1XdZKJ_fw658";    NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(fetchImage:) object:urlStr];    thread.name = @"lisi";    [thread start];}- (void)fetchImage:(NSString*)urlStr{    // 进行耗时的网络请求    [NSThread sleepForTimeInterval:4];    NSURL *url = [NSURL URLWithString:urlStr];    NSData *data = [NSData dataWithContentsOfURL:url];    UIImage *image = [UIImage imageWithData:data];    if ([[NSThread currentThread].name isEqualToString:@"lisi"]) {        BOOL isMainThread = [[NSThread currentThread] isMainThread];        NSLog(@">>>>>isMainThread:%d",isMainThread);    }else{        BOOL isMainThread = [[NSThread currentThread] isMainThread];        NSLog(@"<<<<<<isMainThread:%d",isMainThread);    }    [self performSelectorOnMainThread:@selector(updateImageView:) withObject:image waitUntilDone:YES];}- (void)updateImageView:(UIImage *)image{    if ([[NSThread currentThread] isMainThread]) {        NSLog(@"主线程:%s",__func__);    }    _imageView.image = image;}

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运行结果:
2015-08-02 14:49:31.823 03-NSThreadDemo[3151:781147] -[ViewController dosomething:]
2015-08-02 14:49:34.539 03-NSThreadDemo[3151:781778] >>>>>isMainThread:0
2015-08-02 14:49:34.539 03-NSThreadDemo[3151:780917] 主线程:-[ViewController updateImageView:]

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