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selector
和object
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。
2. 在NSThread中执行Selector
这个话题很简单,直接通过NSObject
的performSelectorInBackground: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NSThread
的detachNewThreadSelector:toTarget:withObject:
静态方法,那么上面NSObject
的performSelectorInBackground: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。
3. 在NSThread中的Run Loop中执行Selector
这里需要的方法是NSObject
的performSelector: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NSRunLoop
的runMode: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];
}