一:異步、同步
1.dispatch_async(dispatch_queue_t queue, dispatch_block_t block);
異步執行
例如: 會立即返回,同時把block裏面加載的東西放在後臺執行。 執行完畢之後 在main(主線程)裏面刷新UI頁面。
// dispatch_queue_t global = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
// dispatch_queue_t mainQ = dispatch_get_main_queue();
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSURL *url = [NSURL URLWithString:@"http://www.ytxww.com/upload/image/201203/20120309100442708165.jpg"];
_img = [UIImage imageWithData:[NSData dataWithContentsOfURL:url]];
_img = [UIImage imageWithData:[NSData dataWithContentsOfURL:url]];
在main(主線程)裏面刷新UI頁面
dispatch_async(dispatch_get_main_queue(), ^{
_imgv.image = _img;
});
});
同樣:
2.dispatch_sync(dispatch_queue_t queue>,(void)block)爲同步執行,和異步不同的是要執行完block塊之後才返回,然後進行下面的操作。
二。dispatch_apply
按照一定次數(size_t iterations)循環,隊列本身決定同步或者異步執行
dispatch_apply(size_t iterations,dispatch_queue_t queue,void (^block)(size_t));
因爲是全部執行完之後才返回,然後繼續執行下面的操作,所以,如果在dispatch_async(異步)裏面添加dispatch_apply可以出現dispatch_sync(同步)的效果。如下:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
dispatch_apply(5, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(size_t index) {
NSLog(@"%zu",index);
});
NSLog(@"會執行五次apply之後,才執行此次打印");
});
三。dispatch_after
延遲執行, 延遲5秒執行打印
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(5 * NSEC_PER_SEC)),dispatch_get_main_queue(), ^{
NSLog(@"after do");
});
四。
1.dispatch_barrier_async
dispatch_barrier_async(dispatch_queue_t queue,dispatch_block_t block);
作用如其名-->阻礙。如下:不管barrier block裏面需要多久,3,4都會在barrier執行完之後執行。
dispatch_queue_t queue = dispatch_queue_create("myqueue", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue, ^(){
NSLog(@"1");
});
dispatch_async(queue, ^(){
NSLog(@"2");
});
dispatch_barrier_async(queue, ^(){
NSLog(@"barrier");
dispatch_apply(10, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(size_t index) {
NSLog(@"......");
});
});
dispatch_async(queue, ^(){
NSLog(@"3");
});
dispatch_async(queue, ^(){
NSLog(@"dispatch-4");
});
和dispatch_barrier_async,大同小異,只是用在同步或者異步的區別。