一：全局队列与并行队列的区别
dispatch_queue_t
q=dispatch_get_global_queue(DISOATCH_QUEUE_PRIORITY_DEFAULT,0);
1.不需要创建，直接get就能用
2.两个队列的执行效果相同
3.全局队列没有名称，调试时，无法确认准确队列
4.全局队列有高中默认优先级
二：并行队列
dispatch_queue_t q =
dispatch_queue_create("fixbird",DISPATCH_QUEUE_CONCURRENT);
三：串行队列
dispatch_queue_t t=
dispatch_queue_create("fixbird",DISPATCH_QUEUE_SERIAL):
四：开发中，跟中当前线程
[NSThread currentThread]
五：并行队列的任务嵌套例子
dispatch_queue_t q =
dispatch_queue_create("fixbird",DISPATCH_QUEUE_CONCURRENT);
//任务嵌套
dispatch_sync(q, ^{
NSLog(@"1 %@", [NSThreadcurrentThread]);
dispatch_sync(q,^{
NSLog(@"2 %@", [NSThreadcurrentThread]);
dispatch_sync(q,^{
NSLog(@"3 %@", [NSThreadcurrentThread]);
});
});
dispatch_async(q,^{
NSLog(@"4 %@", [NSThreadcurrentThread]);
});
NSLog(@"5 %@", [NSThreadcurrentThread]);
});
运行结果：12345或12354
六：主队列（线程）
1每一个应用程序都有一个主线
2所有UI的更新工作，都必须在主线程上执行
3主线程一种工作，而且除非把程序杀掉，否则主线程的工作永不会结束！
dispatch_queue_t q = dispatch_get_main_queue();
七：在主队列上更新UI的例子
//创建代码块
void(^TaskOne)(void) =^(void)
{
NSLog(@"Current thread = %@", [NSThreadcurrentThread]);
NSLog(@"Main thread = %@", [NSThreadmainThread]);
[[[UIAlertView alloc]initWithTitle:@"GCD"
message:@"Great CenterDispatcher"
delegate:nil
cancelButtonTitle:@"OK"
otherButtonTitles:nil, nil] show];
};
//取得分发队列
dispatch_queue_t mainQueue =dispatch_get_main_queue();
//提交任务 dispatch_async(mainQueue,TaskOne);}
//简便写法 dispatch_async( dispatch_get_main_queue(),^(void) { NSLog(@"Current thread = %@", [NSThreadcurrentThread]);
NSLog(@"Main thread = %@", [NSThreadmainThread]);
[[[UIAlertView alloc]initWithTitle:@"GCD"
message:@"Great CenterDispatcher"
delegate:nil
cancelButtonTitle:@"OK"
otherButtonTitles:nil, nil]show];
});
//输出结果
//2014-05-02 20:34:27.872 serirl[835:60b] Current thread = {name
= (null), num = 1}
//2014-05-02 20:34:27.873 serirl[835:60b] Main thread =
{name = (null), num = 1}
八：NSBlockOperation简单实用
//开发中一般给自定义队列定义为属性
@property (nonatomic, strong) NSOperationQueue
*myQueue;
self.myQueue = [[NSOperationQueue alloc] init];
1>在自定义队列
NSBlockOperation *block = [NSBlockOperationblockOperationWithBlock:^{
NSLog(@"%@", [NSThread currentThread]);
}];
所有的自定义队列，都是在子线程中运行.
[self.myQueueaddOperation:block];
或者: [self.myQueue
addOperationWithBlock:^{
NSLog(@"%@", [NSThreadcurrentThread]);
}];
2>在主队列中执行
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
NSLog(@"%@", [NSThreadcurrentThread]);
}];
//设定执行顺序，Dependency依赖，可能会开多个，单不会太多
//依赖关系是够可以跨队列的！
[op2 addDependency:op1];表示op2会在op1执行完之后才会执行
//GCD是串行队列，异步任务，只会开一个县城
[self.myQueue addOperation:op1];
[[NSOperationQueue mainQueue
]addOperation:op4];
九：NSInvocationOperation简单实用
NSInvocationOperation *op = [[NSInvocationOperation
alloc]initWtihTarget:self selector:@selector(demoOp:)
object:@"hello op"];
-(void)demoOp:(id)obj{
NSLog(@"%@ - %@",[NSThread currentThread]);
十：performSelectorOnMainThread方法实用
1模拟下载，延时
[NSThread sleepForTimeInterval:1.0];
2设置图像，苹果底层允许实用performSelectorInBackground方法
在后台县城更新UI，强烈建议大家不要这么做！！！
YES会阻塞住线程，直到调用方法完成
NO不会阻塞县城，会继续执行
[self
performSelectorOnMainThread:@selector(setImage:)
withObject:[UIImage imageNamed:imagePath]
waitUntilDone:NO];
// 1. 图像
- (void)setImage:(UIImage
*)image
{
self.imageView.image =
image;
[self.imageView sizeToFit];
}
11.
提问：代码存在什么问题？如果循环次数非常大，会出现什么问题？应该如何修改？
//
解决办法1：如果i比较大，可以在for循环之后@autoreleasepool //
解决方法2：如果i玩命大，一次循环都会造成
自动释放池被填满,一次循环就@autoreleasepool
for (int i = 0; i < 10000000; ++i)
{
@autoreleasepool
{
//
*
NSString *str = @"Hello
World!";
// new
*
str = [str
uppercaseString];
// new
*
str = [NSString stringWithFormat:@"%@ %d", str,
i];
NSLog(@"%@",
str);
} }