零散知识点

NSInteger转 Byte 数组，长度为2

NSInteger dis = (NSInteger)distanceand ;

Byte val[2] = { (dis >> 8 ) & 0xff , dis & 0x0ff};  

Byte 转 NSData

NSData *data = [NSData dataWithBytes:amd length:sizeof(amd)];

线程保活

dispatch_queue_t queue = dispatch_queue_create("SENDBEAT", DISPATCH_QUEUE_SERIAL);

dispatch_async(queue, ^{

[[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:nil];

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

[thread start];

});

- (void)newThread

{

@autoreleasepool

{

[NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(timer_callback) userInfo:nil repeats:YES];

[[NSRunLoop currentRunLoop] run];

}

}

- (void)timer_callback

{

//  ZHLog(@"根本停不下来");

}