PerformSelector:onThread:withObject:waitUntilDone理解

performSelector:onThread:withObject:waitUntilDone理解

直接看代码

//
//  ViewController.m
//  RunLoopDemo
//

#import "ViewController.h"

@interface ViewController ()
@property (nonatomic, assign) BOOL isAborted;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    [self threadInfo:@"UI"];
    
    _isAborted = NO;
    NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(newThread:) object:nil];
    [thread start];
//    When performing a selector on another thread, the target must have an active run loop
    [self performSelector:@selector(test:) onThread:thread withObject:nil waitUntilDone:NO];
}

- (void)newThread:(id)obj {
    @autoreleasepool {
        NSRunLoop *currentRunLoop = [NSRunLoop currentRunLoop];
        while (!_isAborted) {
            [currentRunLoop runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
        }
        NSLog(@"线程停止");
    }
}

- (void)test:(id)obj {
    [self threadInfo:@"test"];
    _isAborted = YES;
}

- (void)threadInfo:(NSString *)info {
    NSLog(@"%@--%@", info, [NSThread currentThread]);
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
}

@end

有的人无法理解为什么要通过[self performSelector:@selector(test:) onThread:thread withObject:nil waitUntilDone:NO];中的test:方法来更新_isAborted状态。为什么不在[thread start]之后直接调用。原因其实是这里通过selector方法将其设置成yes的原因是虽然设置为yes，但是这时候runloop所在的线程其实是并不知道_isNewThreadAborted被重新赋值了。runloop没有被任务事件唤醒。所以正确的方法是通过使用selector来唤醒Runloop。 并且要注意，在执行performSelector:onThread:withObject:waitUntilDone方法时候，如果是在另外一个线程执行，必须保证另外的线程是有一个runloop.具体的使用可以参考AFNetworking.