GCD的学习
一、任务和队列
1.同步任务 dispatch_sync 不可以开启新线程
dispatch_queue_tqueue =dispatch_queue_create("123",DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue, ^{
dispatch_sync(dispatch_get_main_queue(), ^{
//同步
});
});
2.异步任务 dispatch_async 可以开启新的线程
dispatch_queue_tqueue =dispatch_queue_create("123",DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue, ^{
dispatch_async(dispatch_get_main_queue(), ^{
//异步
});
});
//主线程主队列+同步任务会造成死锁的现象切记不能再主队列里面添加同步任务
dispatch_sync(_queue,^{
dispatch_sync(_queue,^{
//do something
});
})
二、GCD的应用
1-》用于加载图片
dispatch_queue_tqueue =dispatch_queue_create("123",DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue, ^{
NSData*date = [NSDatadataWithContentsOfURL:[NSURLURLWithString:@""]];
UIImage*image = [UIImageimageWithData:date];
dispatch_async(dispatch_get_main_queue(), ^{
//异步
UIImageView*imagesView = [UIImageViewnew];
imagesView.image= image;
});
});
2-》可以用于延时加载
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.3*NSEC_PER_SEC)),dispatch_get_main_queue(), ^{
//延时加载
UIImageView*imagesView = [UIImageViewnew];
imagesView.image= [UIImageimageNamed:@""];
});
3-》可以用于 按秩序 执行代码
dispatch_group_tgroup =dispatch_group_create();
dispatch_group_async(group,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0), ^{
NSLog(@"11111");
});
dispatch_group_async(group,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0), ^{
NSLog(@"22222");
});
dispatch_group_notify(group,dispatch_get_main_queue(), ^{
//在前面两个任务执行完后发送通知执行3333
NSLog(@"3333");
});
4-》 执行一次的代码 比如单例的创建 和 引导页
单例：（也可以用加锁的方式创建）
staticMyViewController*viewVC =nil;
staticdispatch_once_tonceToken;
dispatch_once(&onceToken, ^{
viewVC = [[[selfclass]alloc]init]; //只执行一次
});
5-》多次执行 某段代码
dispatch_apply(10,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0), ^(size_t index) { //index 指的是下标
NSLog(@"index == %zu",index);
});//多次执行
