Grand Central Dispatch 很棒，可以减少代码量，但为什么我不能在后台线程上运行一些东西？
我制作了一个示例应用程序来说明我的意思（没有评论工作）：
- (IBAction)performSel {
[self performSelectorInBackground:@selector(doStuff) withObject:nil];
[NSThread sleepForTimeInterval:3];
[[self.view.subviews lastObject] removeFromSuperview];
}
- (IBAction)gcd {
dispatch_async(dispatch_queue_create("myGCDqueue", NULL), ^(void) {
//dispatch_sync(dispatch_queue_create("myGCDqueue", NULL), ^(void) {
//dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void) {
//dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void) {
//dispatch_async(dispatch_get_main_queue(), ^(void) {
//dispatch_sync(dispatch_get_main_queue(), ^(void) {
[self doStuff]; // only for readability, will move the code on success
});
[NSThread sleepForTimeInterval:3];
[[self.view.subviews lastObject] removeFromSuperview];
}
- (void)doStuff {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc]init];
UIView *abortingView = [[UIView alloc]initWithFrame: self.view.bounds];
abortingView.backgroundColor = [UIColor whiteColor];
abortingView.alpha = 0.7;
[self.view insertSubview:abortingView atIndex:10];
[abortingView release];
[pool drain];
}
这[NSThread sleepForTimeInterval:3];是模拟一个默认的 UI 功能。例如，如果有人从一个导航视图切换到另一个。
只需在新的基于视图的应用程序中复制代码，创建两个按钮并将它们连接起来。