UIButton * btn = [[UIButton alloc]initWithFrame:CGRectMake(100,
100, 100, 100)];
[btn setTitle:@"default"forState:UIControlStateNormal];
btn.backgroundColor = [UIColorblackColor];
[self.view addSubview:btn];
//情况一
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
for( NSInteger i = 0; i < 20;
++ i )
{
sleep(1);
NSLog(@"loop:%d",i);
dispatch_async(dispatch_get_main_queue(), ^{
NSString * str = [NSString stringWithFormat:@"%d",i];
[btn setTitle:str forState:UIControlStateNormal];
});
}
});
//情况二
/*
dispatch_queue_t serQ =
dispatch_queue_create("rock", DISPATCH_QUEUE_SERIAL);
dispatch_async(serQ, ^{
for( NSInteger i = 0; i < 20; ++ i
)
{
sleep(1);
NSLog(@"loop:%d",i);
dispatch_async(dispatch_get_main_queue(), ^{
NSString *
str = [NSString stringWithFormat:@"%d",i];
[btn
setTitle:str forState:UIControlStateNormal];
});
}
});
*/
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
当某几个任务执行完毕之后，接着执行另外一个任务，那就应该使用dispatch group 这个功能了
dispatch_group_t group =
dispatch_group_create();
dispatch_group_async(group, dispatch_get_global_queue(0, 0), ^{
for( NSInteger i = 0; i < 10;
++ i )
{
sleep(1);
NSLog(@"loop1:%d",i);
}
});
dispatch_group_async(group,dispatch_get_global_queue(0, 0),^{
for( NSInteger i = 0; i < 10;
++ i )
{
sleep(1);
NSLog(@"loop2:%d",i);
}
});
dispatch_group_notify(group, dispatch_get_global_queue(0, 0), ^{
NSLog(@"done");
});