IOS GCD之Block
GCD延迟执行
#pragma mark - GCD 延迟
/**
* dispatch_after
*/
- (void)gcdDelay
{
NSLog(@"开始时间。。。。。。。%@",[NSDate date]);
double delaySecond = 2.0;
dispatch_time_t delayInNanoSeconds = dispatch_time(DISPATCH_TIME_NOW, delaySecond*NSEC_PER_SEC);
//得到当前的全局队列
dispatch_queue_t concurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_after(delayInNanoSeconds, concurrentQueue, ^(void){
NSLog(@"延迟两秒执行......%@",[NSDate date]);
});
}
C函数执行如下
/**
* dispatch_after_f 执行的是一个纯C函数（processSomething）
*/
- (void)gcdDelay_t
{
NSLog(@"开始时间。。。。。。。%@",[NSDate date]);
double delaySecond = 2.0;
dispatch_time_t delayInNanoSeconds = dispatch_time(DISPATCH_TIME_NOW, delaySecond*NSEC_PER_SEC);
//得到当前的全局队列
dispatch_queue_t concurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
//dispatch_after_f 执行的是一个纯C函数（processSomething）
dispatch_after_f(delayInNanoSeconds, concurrentQueue, @"GCD", processSomething);
}
void processSomething(void *paramContext){
NSLog(@"%@",paramContext);
}
2.GCD单例
- (void)gcdSingle
{
static dispatch_once_t onceTocken;
void (^executedOnlyOnce)(void) = ^{
static NSUInteger numberOfEntries = 0;
numberOfEntries++;
NSLog(@"Executed %lu time(s)", (unsigned long)numberOfEntries);
};
dispatch_queue_t concurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_once(&onceTocken, ^(void){
dispatch_async(concurrentQueue, executedOnlyOnce);
});
dispatch_once(&onceTocken, ^(void){
dispatch_async(concurrentQueue, executedOnlyOnce);
});
}
可以发现，输出只有一行，虽然我们调用了2次，因为我们传入的dispatch_once_t是相同的，编译器只执行一次。
3.GCD 队列调度
/**
* 问题：我对每个任务用的是方法dispatch_group_async，是异步的啊。为什么顺序却不变呢？
* 解答:因为他们都是分配给同一个队列dispatch_get_main_queue() 中的！在一个队列中是串行的啊。所以，还是按照顺序来。
*/
- (void)gcdGroup
{
// 创建一个调度组
dispatch_group_t taskGroup = dispatch_group_create();
// 创建队列
dispatch_queue_t mainQueue = dispatch_get_main_queue();
// 任务1
// 将Block添加到指定的调度组(taskGroup)中，并且该Block用指定的队列(mainQueue)执行。
dispatch_group_async(taskGroup, mainQueue, ^{
[self reloadTableView];
});
// 任务2
// 将Block添加到指定的调度组(taskGroup)中，并且该Block用指定的队列(mainQueue)执行。
dispatch_group_async(taskGroup, mainQueue, ^{
[self reloadScrollView];
});
// 任务3
// 将Block添加到指定的调度组(taskGroup)中，并且该Block用指定的队列(mainQueue)执行。
dispatch_group_async(taskGroup, mainQueue, ^{
[self reloadImageView];
});
dispatch_group_notify(taskGroup, mainQueue, ^{
[[[UIAlertView alloc] initWithTitle:@"完成" message:@"所有调度完成" delegate:nil cancelButtonTitle:@"完成" otherButtonTitles:nil, nil] show];
});
}
/**
* 因为dispatch_group_async_f不像dispatch_group_t那样使用Block，可以访问当前类的变量。
* 由于 dispatch_group_async_f 接受 C 函数作为一个代码块来执行,所以，我们要执行reloadTableView方法，reloadScrollView方法，reloadImageView方法，必须有个当前类的引用！！！！！
* 那么 C 函数必须有一 个引用到 Self,这个 Self 能够调用当前对象的实例方法
*
*/
/**
* C函数的写法
*/
- (void)gcdGroup_c
{
// 创建一个调度组
dispatch_group_t taskGroup = dispatch_group_create();
// 创建队列
dispatch_queue_t mainQueue = dispatch_get_main_queue();
dispatch_group_async_f(taskGroup, mainQueue, (__bridge void *)self, reloadAllComponents);
}
void reloadAllComponents(void *context)
{
ViewController *self = (__bridge ViewController *)context;
[self reloadTableView];
[self reloadScrollView];
[self reloadImageView];
}
4.自定义队列调度
- (void)gcdCustomeGroup
{
dispatch_queue_t firstSerialQueue = dispatch_queue_create("com.sinoicity.gcd", NULL);
dispatch_async(firstSerialQueue, ^{
NSUInteger counter = 0;
for (counter = 0; counter < 5; counter++){
NSLog(@"First iteration, counter = %lu", (unsigned long)counter);
}
NSLog(@"Current thread = %@", [NSThread currentThread]);
});
dispatch_async(firstSerialQueue, ^{
NSUInteger counter = 0;
for (counter = 0; counter < 5; counter++){
NSLog(@"Second iteration, counter = %lu", (unsigned long)counter);
}
NSLog(@"Current thread = %@", [NSThread currentThread]);
});
dispatch_async(firstSerialQueue, ^{
NSUInteger counter = 0;
for (counter = 0; counter < 5; counter++){
NSLog(@"Third iteration, counter = %lu", (unsigned long)counter);
}
NSLog(@"Current thread = %@", [NSThread currentThread]);
});
dispatch_queue_t mainQueue = dispatch_get_main_queue();
dispatch_async(mainQueue, ^{
NSLog(@"Main thread = %@", [NSThread mainThread]);
});
}
注意：我们自定义的队列，往往不会在主队列中执行。而是单独分配一个线程来维护我们所定义的队列。