#线程间通讯

• 从网络中下载一张图片放入到UIImageView中

- (void)touchBegin:(NSSet *)touches withEvent:(UIEvent *)event{    //1.下载图片    /*    //测试执行时间    //NSDate *begin = [NSDate date];    CFAbsoluteTime begin = CFAbsoluterTimeGetCurrent();        //从网络下载一张图片    NSURL *url = [NSURL URLWihtString:@"图片资源网址"];    NSData *data = [NSData dataWithContentsOfURL:url];//耗时,应开启子线程        //NSDate *end = [NSDate date];    //NSLog(@"%f",[end timeIntervalSincedate:begin]);    CFAbsoluteTime end = CFAbsoluteTimeGetCurrent();    NSLog(@"%f",end - begin);        //2.将二进制转换为图片    UIImage *image = [UIImage imageWithData:data];    //3.显示图片    self.imageView.image = image;    */        //开启一个子线程,下载图片    [self performSelectorInBackground:@selector(download) withObject:nil];}

• 在主线程中下载图片会影响性能,应该开启一个子线程

- (void)download{    //1.下载图片    NSURL *url = [NSURL URLWihtString:@"图片资源网址"];    NSData *data = [NSData dataWithContentsOfURL:url];//耗时,应开启子线程        //2.将二进制转换为图片    UIImage *image = [UIImage imageWithData:data];        //3.更新UI#warning 注意:千万不要再子线程中更新UI,会出问题    //self.imageView.image = image;//不能子子线程中更新UI    //在主线程中更新UI    [self performSelectorOnMainThread:@selector(setImage:) withObject:image waitUntilDone:YES];//开发中常用        //[self performSelectorOnMainThread:@selector(updateImage:) withObject:image waitUntilDone:YES];        NSLog(@"------");}- (void)updateImage:(UIImage *)image{    NSLog(@"++++++++");    self.imageView.image = image;}

• waitUntilDone:
  • 如果传入YES,那么会等待@selector中的函数执行完毕,就可以执行之后的代码
  • 如果传入NO,那么不会等待@selector中的函数执行完毕,就可以执行之后的代码

更新UI的方法

• 1.使用setImage:(开发中常用)

[self performSelectorOnMainThread:@selector(setImage:) withObject:image waitUntilDone:YES];

• 2.使用自定义函数:(了解)

[self performSelectorOnMainThread:@selector(updateImage:) withObject:image waitUntilDone:YES];  - (void)updateImage:(UIImage *)image{    self.imageView.image = image;}

• 3.使用:performSelector:(了解)
  • 可以在指定的线程中,调用指定对象的指定方法

[self performSelector:@selector(updateImage:) onThread:[NSThread mainThread] withObject:image waitUntilDone:YES]; - (void)updateImage:(UIImage *)image{    self.imageView.image = image;}