NSObject 中执行Selector 的相关方法

1. 对当前Run Loop中Selector Sources的取消

NSObject中的performSelector:withObject:afterDelay:方法将会在当前线程的Run Loop中根据afterDelay参数创建一个Timer,如果没有调用有inModes参数的方法,该Timer会运行在当前Run Loop的默认模式中,也就是NSDefaultRunLoopMode定义的模式中。

performSelector:withObject:afterDelay:方法的使用看起来还是很简单的。这里讲另外一个辅助函数,NSObject中静态的cancelPreviousPerformRequestsWithTarget方法。该方法就是专门用来取消取消performSelector:withObject:afterDelay:方法所创建的Selector source(内部上就是一个Run Loop的Timer source)。因此该方法和performSelector:withObject:afterDelay:方法一样,只限于当前Run Loop中。

我们可以利用cancelPreviousPerformRequestsWithTarget直接取消一个对象在当前Run Loop中的所有未执行的performSelector:withObject:afterDelay:方法所产生的Selector Sources,如下代码:

- (void)viewDidLoad
{
[super viewDidLoad]; [self performSelector:@selector(test:) withObject:nil afterDelay:1];
[self performSelector:@selector(test:) withObject:@"mgen" afterDelay:2];
[NSObject cancelPreviousPerformRequestsWithTarget:self];
} - (void)test:(id)obj
{
NSLog(@"调用成功: %@", obj);
}

不会有任何输出,因为两个调用都被取消了。

如果想取消单独一个的话,需使用cancelPreviousPerformRequestsWithTarget:selector:object:方法,注意selectorobject参数需要一一对应。如下代码:

- (void)viewDidLoad
{
[super viewDidLoad]; [self performSelector:@selector(test:) withObject:[NSNumber numberWithInt:26] afterDelay:1];
[self performSelector:@selector(test:) withObject:[NSNumber numberWithInt:17] afterDelay:2];
[self performSelector:@selector(test:) withObject:[NSNumber numberWithInt:17] afterDelay:3];
[NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(test:) object:[NSNumber numberWithInt:17]];
} - (void)test:(id)obj
{
NSLog(@"调用成功: %@", obj);
}

只会输出:

调用成功: 26

其他两个Selector都被取消了。

返回目录

2. 在NSThread中执行Selector

这个话题很简单,直接通过NSObjectperformSelectorInBackground:withObject:方法就可以,如下代码:

- (void)viewDidLoad
{
[super viewDidLoad]; [self threadInfo:@"UI"];
[self performSelectorInBackground:@selector(test:) withObject:nil]; } - (void)test:(id)obj
{
@autoreleasepool
{
[self threadInfo:@"test"];
}
}
- (void)threadInfo:(NSString*)category
{
NSLog(@"%@ - %@", category, [NSThread currentThread]);
}

输出:

UI - <NSThread: 0x71639e0>{name = (null), num = 1}
test - <NSThread: 0x7176ad0>{name = (null), num = 3}

这个方法完全等效于NSThreaddetachNewThreadSelector:toTarget:withObject:静态方法,那么上面NSObjectperformSelectorInBackground:withObject:方法调用完全可以替换成:

[NSThread detachNewThreadSelector:@selector(test:) toTarget:self withObject:nil];

当然,用户也可以自行手动创建一个NSThread来完成上述功能,代码如下:

NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(test:) object:nil];
[thread start];

这两种方法运行后的输出是和第一种类似的。

返回目录

3. 在NSThread中的Run Loop中执行Selector

这里需要的方法是NSObjectperformSelector:onThread:withObject:waitUntilDone:方法。由于是在另一个NSThread中执行Selector,所以我们需要手动开始Run Loop。首先需要在ViewController中定义两个字段,分别是NSThread和控制线程内Run Loop执行的flag。

@interface ViewController ()
{
NSThread *_thread;
BOOL _isNewThreadAborted;
}

接下来做的是执行这个线程,并且在线程中手动调用NSRunLooprunMode:beforeDate:方法。这里注意,如果Run Loop没有任何Source的话,该方法会立即返回,所以需要创建一个循环来持续调用Run Loop的runMode:beforeDate:方法。并在Selector执行结束后同时尝试结束这个循环。最终代码如下:

- (void)viewDidLoad
{
[super viewDidLoad]; [self threadInfo:@"UI"]; _isNewThreadAborted = NO;
_thread = [[NSThread alloc] initWithTarget:self selector:@selector(newThread:) object:nil];
//开始线程
[_thread start];
//在另一个线程中的Run Loop中执行Selector
[self performSelector:@selector(test:) onThread:_thread withObject:nil waitUntilDone:NO];
} //在新线程中创建并开始一个NSRunLoop
- (void)newThread:(id)obj
{
@autoreleasepool
{
NSRunLoop *currentRunLoop = [NSRunLoop currentRunLoop];
while (!_isNewThreadAborted)
{
[currentRunLoop runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
}
NSLog(@"线程停止");
}
} //Selector执行
- (void)test:(id)obj
{
[self threadInfo:@"test"];
_isNewThreadAborted = YES;
} - (void)threadInfo:(NSString*)category
{
NSLog(@"%@ - %@", category, [NSThread currentThread]);
}

输出:

UI - <NSThread: 0x717e7e0>{name = (null), num = 1}
test - <NSThread: 0x8078a80>{name = (null), num = 3}
线程停止

最后注意performSelector:onThread:withObject:waitUntilDone:方法中最后的waitUntilDone参数,如果传YES的话,当前线程会等待Selector在另一个线程中执行完毕后继续执行。

4. UIPinchGestureRecognizer 与 NSObject Selector 的关联

if (recognizer.state == UIGestureRecognizerStateChanged) {

[NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(XXXSetNeedsDisplay) object:recognizer];

    // 相关的方法...

} else if (recognizer.state == UIGestureRecognizerStateEnded) {

[self performSelector:@selector(XXXSetNeedsDisplay) withObject:recognizer afterDelay:1.0f];

}

上一篇:原生JS和jQuery操作DOM的区别小结


下一篇:两个和尚抬水有水喝,三个和尚抬水没水喝------IT项目管理之组织架构