全局并发队列//添加touch事件显示图片
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
//1获得主队列 线程之间的通讯
//异步并行
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//执行操作
NSString *str=@"http://a.hiphotos.baidu.com/baike/c0%3Dbaike150%2C5%2C5%2C150%2C50/sign=1dc843d302087bf469e15fbb93ba3c49/6a63f6246b600c338719a2501a4c510fd8f9a1c1.jpg";
NSURL *url=[NSURL URLWithString:str];
NSData *data=[NSData dataWithContentsOfURL:url];
UIImage *image=[UIImage imageWithData:data];
//回到主线程显示图片
dispatch_async(dispatch_get_main_queue(), ^{
self.imageview.image=image;
});
});
}
//-------------------
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//执行耗时的异步操作
dispatch_async(dispatch_get_main_queue(), ^{
//回到主线程，执行ui刷新操作
});
});
全局并发队列 手动创建串行队列 主队列
dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0) dispatch_queue_create("queue名字", nil) dispatch_get_main_queue()
同步sync 没有开启新线程(不具备开启新线程的能力) 串行执行任务 没有开启新线程 串行执行任务 没有开启新线程 串行执行任务(死循环)
异步async 有开启新线程(具备开启新线程的能力) 并发执行任务 有开启新线程 串行执行 任务 有开启新线程 串行执行任务
//点击事件下载图片 两张图片合成一张图片显示
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
dispatch_group_t group=dispatch_group_create();
__block UIImage *image1=nil;
dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
image1=[self imageWithurl:@"http://news.xinhuanet.com/mil/2015-08/21/128150615_14401105350931n.jpg"];
});
__block UIImage *image2=nil;
dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
image2= [self imageWithurl:@"http://news.xinhuanet.com/mil/2015-08/21/128150615_14401105352811n.jpg"];
});
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
self.image1.image=image1;
self.image2.image=image2;
//合并图片
UIGraphicsBeginImageContextWithOptions(CGSizeMake(200, 120), NO, 0.0);
[image1 drawInRect:CGRectMake(0, 0, 100, 120)];
[image2 drawInRect:CGRectMake(100, 0, 100, 120)];
self.addimage.image=UIGraphicsGetImageFromCurrentImageContext();
//关闭上下文
UIGraphicsEndImageContext();
});
}
//请求一个图片
-(UIImage *)imageWithurl:(NSString *)urlstr{
//1
NSURL *url=[NSURL URLWithString:urlstr];
NSData *data=[NSData dataWithContentsOfURL:url];
UIImage *image=[UIImage imageWithData:data];
NSLog(@"转图片");
return image;
}