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关于performSelector的一些小探讨

2018-12-05 20:37 出处:清屏网 人气: 评论(0

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    NSLog(@"1 - %@", [NSThread currentThread]);
    
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        
        NSLog(@"2 - %@", [NSThread currentThread]);
        [self performSelector:@selector(test)
                   withObject:nil];
        NSLog(@"4 - %@", [NSThread currentThread]);
    });
}
	
- (void)test
{
    NSLog(@"3 - %@", [NSThread currentThread]);
    
}
  • 输出结果: 1,2,3,4
  • 原因: 因为 performSelector:withObject: 会在当前线程立即执行指定的 selector 方法。

例子②:

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    NSLog(@"1 - %@", [NSThread currentThread]);
    
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        
        NSLog(@"2 - %@", [NSThread currentThread]);
        [self performSelector:@selector(test)
                   withObject:nil
                   afterDelay:0];
        NSLog(@"4 - %@", [NSThread currentThread]);
    });
}
	
- (void)test
{
    NSLog(@"3 - %@", [NSThread currentThread]);
}
  • 输出结果: 1,2,4
  • 原因: 因为 performSelector:withObject:afterDelay: 实际是往 RunLoop 里面注册一个定时器,而在子线程中,RunLoop 是没有开启(默认)的,所有不会输出 3 。官网 API 作如下解释:

例子③:

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    NSLog(@"1 - %@", [NSThread currentThread]);
    
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        
        NSLog(@"2 - %@", [NSThread currentThread]);
        [self performSelector:@selector(test)
                   withObject:nil
                   afterDelay:0];
        [[NSRunLoop currentRunLoop] run];
        NSLog(@"4 - %@", [NSThread currentThread]);
    });
}
	
- (void)test
{
    NSLog(@"3 - %@", [NSThread currentThread]);
}
  • 输出结果: 1,2,3,4
  • 原因: 由于 [[NSRunLoop currentRunLoop] run]; 会创建的当前子线程对应的 RunLoop 对象并启动了,因此可以执行 test 方法;并且 test 执行完后,RunLoop 中注册的定时器已经无效,所以还可以输出 4 (对比 例子⑥例子 )。

例子④:

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    NSLog(@"1 - %@", [NSThread currentThread]);
    
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        
        NSLog(@"2 - %@", [NSThread currentThread]);
        [self performSelector:@selector(test)
                     onThread:[NSThread currentThread]
                   withObject:nil
                waitUntilDone:YES];
        NSLog(@"4 - %@", [NSThread currentThread]);
    });
}
	
- (void)test
{
    NSLog(@"3 - %@", [NSThread currentThread]);
}
  • 输出结果: 1,2,3,4
  • 原因:因为 performSelector:onThread:withObject:waitUntilDone: 会在指定的线程执行,而执行的策略根据参数 wait 处理,这里传 YES 表明将会立即阻断 指定的线程 并执行指定的 selector 。官网 API 解释如下:

例子⑤:

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    NSLog(@"1 - %@", [NSThread currentThread]);
    
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        
        NSLog(@"2 - %@", [NSThread currentThread]);
        [self performSelector:@selector(test)
                     onThread:[NSThread currentThread]
                   withObject:nil
                waitUntilDone:NO];
        NSLog(@"4 - %@", [NSThread currentThread]);
    });
}
	
- (void)test
{
    NSLog(@"3 - %@", [NSThread currentThread]);
}
  • 输出结果: 1,2,4
  • 原因:因为 performSelector:onThread:withObject:waitUntilDone: 会在指定的线程执行,而执行的策略根据参数 wait 处理,这里传 NO 表明不会立即阻断 指定的线程 而是将 selector 添加到指定线程的 RunLoop 中等待时机执行。(该例子中,子线程 RunLoop 没有启动,所有没有输出 3 )官网 API 解释如下:

例子⑥:

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    NSLog(@"1 - %@", [NSThread currentThread]);
    
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        
        NSLog(@"2 - %@", [NSThread currentThread]);
        [self performSelector:@selector(test)
                     onThread:[NSThread currentThread]
                   withObject:nil
                waitUntilDone:NO];
        [[NSRunLoop currentRunLoop] run];
        NSLog(@"4 - %@", [NSThread currentThread]);
    });
}
	
- (void)test
{
    NSLog(@"3 - %@", [NSThread currentThread]);
}
  • 输出结果: 1,2,3
  • 原因: 由于 [[NSRunLoop currentRunLoop] run]; 已经创建的当前子线程对应的 RunLoop 对象并启动了,因此可以执行 test 方法;但是 test 方法执行完后,RunLoop 并没有结束(使用这种启动方式,RunLoop 会一直运行下去,在此期间会处理来自输入源的数据,并且会在 NSDefaultRunLoopMode 模式下重复调用 runMode:beforeDate: 方法)所以无法继续输出 4

例子⑦

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    NSLog(@"1 - %@", [NSThread currentThread]);
    
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        
        NSLog(@"2 - %@", [NSThread currentThread]);
        [self performSelector:@selector(test)
                     onThread:[NSThread currentThread]
                   withObject:nil
                waitUntilDone:NO];
        [[NSRunLoop currentRunLoop] runUntilDate:[NSDate distantFuture]];
        NSLog(@"4 - %@", [NSThread currentThread]);
    });
}
	
- (void)test
{
    NSLog(@"3 - %@", [NSThread currentThread]);
}
  • 输出结果: 1,2,3
  • 原因: 由于 [[NSRunLoop currentRunLoop] runUntilDate:[NSDate distantFuture]]; 已经创建的当前子线程对应的 RunLoop 对象并启动了,因此可以执行 test 方法;但是 test 方法执行完后,RunLoop 并没有结束(使用这种启动方式,可以设置超时时间,在超时时间到达之前,runloop会一直运行,在此期间runloop会处理来自输入源的数据,并且会在 NSDefaultRunLoopMode 模式下重复调用 runMode:beforeDate: 方法)所以无法继续输出 4

例子⑧:

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    NSLog(@"1 - %@", [NSThread currentThread]);
    
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        
        NSLog(@"2 - %@", [NSThread currentThread]);
        [self performSelector:@selector(test)
                     onThread:[NSThread currentThread]
                   withObject:nil
                waitUntilDone:NO];
        [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode
                                 beforeDate:[NSDate distantFuture]];
        NSLog(@"4 - %@", [NSThread currentThread]);
    });
}
	
- (void)test
{
    NSLog(@"3 - %@", [NSThread currentThread]);
}
  • 输出结果: 1,2,3,4
  • 原因: 由于 [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]]; 已经创建的当前子线程对应的 RunLoop 对象并启动了,因此可以执行 test 方法;而且 test 方法执行完后,RunLoop 立刻结束(使用这种启动方式 ,RunLoop 会运行一次,超时时间到达或者第一个 input source 被处理,则 RunLoop 就会退出)所以可以继续输出 4

小结:

  1. 常用 performSelector 方法

    • 常用的 perform ,是 NSObject.h 头文件下的方法:

      - (id)performSelector:(SEL)aSelector;
      - (id)performSelector:(SEL)aSelector withObject:(id)object;
      - (id)performSelector:(SEL)aSelector withObject:(id)object1 withObject:(id)object2;
      
    • 可以 delay perform ,是 NSRunLoop.h 头文件下的方法:

      - (void)performSelector:(SEL)aSelector withObject:(nullable id)anArgument afterDelay:(NSTimeInterval)delay inModes:(NSArray<NSRunLoopMode> *)modes;
      - (void)performSelector:(SEL)aSelector withObject:(nullable id)anArgument afterDelay:(NSTimeInterval)delay;
      
    • 可以 指定线程 perform ,是 NSThread 头文件下的方法:

      - (void)performSelectorOnMainThread:(SEL)aSelector withObject:(nullable id)arg waitUntilDone:(BOOL)wait modes:(nullable NSArray<NSString *> *)array;
      - (void)performSelectorOnMainThread:(SEL)aSelector withObject:(nullable id)arg waitUntilDone:(BOOL)wait;
      - (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(nullable id)arg waitUntilDone:(BOOL)wait modes:(nullable NSArray<NSString *> *)array;
      - (void)performSelector:(SEL)aSelector onThread:(NSThread *)thr withObject:(nullable id)arg waitUntilDone:(BOOL)wait;
      - (void)performSelectorInBackground:(SEL)aSelector withObject:(nullable id)arg;
      
  2. RunLoop 退出方式:

    • 使用 - (void)run; 启动,RunLoop 会一直运行下去,在此期间会处理来自输入源的数据,并且会在 NSDefaultRunLoopMode 模式下重复调用 runMode:beforeDate: 方法;
    • 使用 - (void)runUntilDate:(NSDate *)limitDate; 启动,可以设置超时时间,在超时时间到达之前,RunLoop 会一直运行,在此期间 RunLoop 会处理来自输入源的数据,并且也会在 NSDefaultRunLoopMode 模式下重复调用 runMode:beforeDate: 方法;
    • 使用 - (void)runMode:(NSString *)mode beforeDate:(NSDate *)limitDate; 启动,RunLoop 会运行一次,超时时间到达或者第一个 input source 被处理,则 RunLoop 就会退出。

更多关于 NSRunLoop的退出方式 可以看这篇 博文


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