05-线程间通讯

线程间通讯

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• 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;
}