方法一
先下载第1张图片，然后下载第2张图片，最后合并图片
弊病：由于图片比较耗时，一张一张的下载图片更耗时。
// 异步下载
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// 1.下载第1张
NSURL *url1 = [NSURL URLWithString:@"http://g.hiphotos.baidu.com/image/pic/item/f2deb48f8c5494ee460de6182ff5e0fe99257e80.jpg"];
NSData *data1 = [NSData dataWithContentsOfURL:url1];
UIImage *image1 = [UIImage imageWithData:data1];
// 2.下载第2张
NSURL *url2 = [NSURL URLWithString:@"http://su.bdimg.com/static/superplus/img/logo_white_ee663702.png"];
NSData *data2 = [NSData dataWithContentsOfURL:url2];
UIImage *image2 = [UIImage imageWithData:data2];
// 3.合并图片
// 开启一个位图上下文
UIGraphicsBeginImageContextWithOptions(image1.size, NO, 0.0);
// 绘制第1张图片
CGFloat image1W = image1.size.width;
CGFloat image1H = image1.size.height;
[image1 drawInRect:CGRectMake(0, 0, image1W, image1H)];
// 绘制第2张图片
CGFloat image2W = image2.size.width * 0.5;
CGFloat image2H = image2.size.height * 0.5;
CGFloat image2Y = image1H - image2H;
[image2 drawInRect:CGRectMake(0, image2Y, image2W, image2H)];
// 得到上下文中的图片
UIImage *fullImage = UIGraphicsGetImageFromCurrentImageContext();
// 结束上下文
UIGraphicsEndImageContext();
// 4.回到主线程显示图片
dispatch_async(dispatch_get_main_queue(), ^{
self.imageView.image = fullImage;
});
});
方法二
同时开启两个线程分别下载图片
弊病：增加额外的属性
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
// 异步下载
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// 1.下载第1张
NSURL *url1 = [NSURL URLWithString:@"http://g.hiphotos.baidu.com/image/pic/item/f2deb48f8c5494ee460de6182ff5e0fe99257e80.jpg"];
NSData *data1 = [NSData dataWithContentsOfURL:url1];
self.image1 = [UIImage imageWithData:data1];
[self bindImages];
});
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// 2.下载第2张
NSURL *url2 = [NSURL URLWithString:@"http://su.bdimg.com/static/superplus/img/logo_white_ee663702.png"];
NSData *data2 = [NSData dataWithContentsOfURL:url2];
self.image2 = [UIImage imageWithData:data2];
[self bindImages];
});
}
- (void)bindImages
{
if (self.image1 == nil || self.image2 == nil) return;
// 3.合并图片
// 开启一个位图上下文 （相当于创建了一个空的图片）
// UIGraphicsBeginImageContextWithOptions(<#CGSize size#>（新的图片有多大）, <#BOOL opaque#>（NO代表透明，YES代表不透明）, <#CGFloat scale#> （缩放比例）)
UIGraphicsBeginImageContextWithOptions(self.image1.size, NO, 0.0);
// 绘制第1张图片 （绘制到上面创建的那个位图上下文上面 也就是那张空的图片上面）
CGFloat image1W = self.image1.size.width;
CGFloat image1H = self.image1.size.height;
[self.image1 drawInRect:CGRectMake(0, 0, image1W, image1H)];
// 绘制第2张图片
CGFloat image2W = self.image2.size.width * 0.5;
CGFloat image2H = self.image2.size.height * 0.5;
CGFloat image2Y = image1H - image2H;
//把image2 绘制到后面的那个区域
[self.image2 drawInRect:CGRectMake(0, image2Y, image2W, image2H)];
// 得到上下文中的图片
UIImage *fullImage = UIGraphicsGetImageFromCurrentImageContext();
// 结束上下文
UIGraphicsEndImageContext();
// 4.回到主线程显示图片
dispatch_async(dispatch_get_main_queue(), ^{
self.imageView.image = fullImage;
});
}
方法三
队列组
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
// 1.队列组
dispatch_group_t group = dispatch_group_create();
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
// 2.下载图片1
__block UIImage *image1 = nil; //要加一个 __block因为 block代码默认不能改外面的东西（记住语法即可）
dispatch_group_async(group, queue, ^{
NSURL *url1 = [NSURL URLWithString:@"http://g.hiphotos.baidu.com/image/pic/item/f2deb48f8c5494ee460de6182ff5e0fe99257e80.jpg"];
NSData *data1 = [NSData dataWithContentsOfURL:url1];
image1 = [UIImage imageWithData:data1];
});
// 3.下载图片2
__block UIImage *image2 = nil;
dispatch_group_async(group, queue, ^{
NSURL *url2 = [NSURL URLWithString:@"http://su.bdimg.com/static/superplus/img/logo_white_ee663702.png"];
NSData *data2 = [NSData dataWithContentsOfURL:url2];
image2 = [UIImage imageWithData:data2];
});
// 4.合并图片 用Quartz2D的知识，则要先要搞一个空的大图片，然后再把小图片画上去(保证执行完组里面的所有任务之后，再执行notify函数里面的block)
//队列组：要把队列组里面的所有任务都执行完后调用dispatch_group_notify(group, queue, ^{ }
dispatch_group_notify(group, queue, ^{
// 开启一个位图上下文
UIGraphicsBeginImageContextWithOptions(image1.size, NO, 0.0);
// 绘制第1张图片
CGFloat image1W = image1.size.width;
CGFloat image1H = image1.size.height;
[image1 drawInRect:CGRectMake(0, 0, image1W, image1H)];
// 绘制第2张图片
CGFloat image2W = image2.size.width * 0.5;
CGFloat image2H = image2.size.height * 0.5;
CGFloat image2Y = image1H - image2H;
[image2 drawInRect:CGRectMake(0, image2Y, image2W, image2H)];
// 得到上下文中的图片
UIImage *fullImage = UIGraphicsGetImageFromCurrentImageContext();
// 结束上下文
UIGraphicsEndImageContext();
// 5.回到主线程显示图片
dispatch_async(dispatch_get_main_queue(), ^{
self.imageView.image = fullImage;
});
});
}
参考 ** iOS开发多线程之队列组——下载合并图片**
方法四
线程依赖
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
/**
假设有A、B、C三个操作，要求：
1. 3个操作都异步执行
2. 操作C依赖于操作A
3. 操作C依赖于操作B
*/
//创建一个队列
NSOperationQueue *queue = [[NSOperationQueue alloc]init];
//可开辟线程的最大数量
queue.maxConcurrentOperationCount = 3;
//创建三个任务
NSBlockOperation *operationA = [NSBlockOperation blockOperationWithBlock:^{
NSURL *url1 = [NSURL URLWithString:@"http://g.hiphotos.baidu.com/image/pic/item/f2deb48f8c5494ee460de6182ff5e0fe99257e80.jpg"];
NSData *data1 = [NSData dataWithContentsOfURL:url1];
self.image1 = [UIImage imageWithData:data1];
}];
NSBlockOperation *operationB = [NSBlockOperation blockOperationWithBlock:^{
NSURL *url2 = [NSURL URLWithString:@"https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1504108008401&di=6297b96e3a13728c58d806b71e4590bb&imgtype=0&src=http%3A%2F%2Fwww.logoing.net%2Fwp-content%2Fuploads%2F2012%2F08%2Fbaidulogo1.jpg"];
NSData *data2 = [NSData dataWithContentsOfURL:url2];
self.image2 = [UIImage imageWithData:data2];
}];
NSBlockOperation *operationC = [NSBlockOperation blockOperationWithBlock:^{
// 开启一个位图上下文
UIGraphicsBeginImageContextWithOptions(self.image1.size, NO, 0.0);
// 绘制第1张图片
CGFloat image1W = self.image1.size.width;
CGFloat image1H = self.image1.size.height;
[self.image1 drawInRect:CGRectMake(0, 0, image1W, image1H)];
// 绘制第2张图片
CGFloat image2W = self.image2.size.width * 0.5;
CGFloat image2H = self.image2.size.height * 0.5;
CGFloat image2Y = image1H - image2H;
[self.image2 drawInRect:CGRectMake(0, image2Y, image2W, image2H)];
// 得到上下文中的图片
UIImage *fullImage = UIGraphicsGetImageFromCurrentImageContext();
// 结束上下文
UIGraphicsEndImageContext();
// 5.回到主线程显示图片
dispatch_async(dispatch_get_main_queue(), ^{
self.ww_imgView.image = fullImage;
});
}];
//设置任务之间的依赖
[operationC addDependency:operationA];
[operationC addDependency:operationB];
//添加操作到队列中-自动异步执行，并发
[queue addOperation:operationA];
[queue addOperation:operationB];
[queue addOperation:operationC];
}
