异步图片GCD下载

最新推荐文章于 2019-04-11 15:07:47 发布

原创最新推荐文章于 2019-04-11 15:07:47 发布 · 317 阅读

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#异步图片下载 #gcd

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准备工作：

dispatch_queue_t disqueue = dispatch_queue_create("myqueue", DISPATCH_QUEUE_CONCURRENT);
    dispatch_group_t disgroup = dispatch_group_create();
    __weak ViewController *weakSelf = self;

第一张图片:

dispatch_group_async(disgroup, disqueue, ^{
        NSLog(@"开始第一项任务");
        NSURL *url = [NSURL URLWithString:@"http://www.poluoluo.com/qq/UploadFiles_7828/201611/2016110420035637.jpg"];
        @try {
            NSData *data = [[NSData alloc] initWithContentsOfURL:url];
            if (data) {
                leftData = data;
                dispatch_async(dispatch_get_main_queue(), ^{
                    weakSelf.leftImageView.image = [UIImage imageWithData:data];
                });
            }
        } @catch (NSException *exception) {
            NSLog(@"下载图片1出错啦");
        }
        NSLog(@"第一项任务完成");
    });

第二张图片:

dispatch_group_async(disgroup, disqueue, ^{
        NSLog(@"开始第二项任务");
        NSURL *url = [NSURL URLWithString:@"http://www.poluoluo.com/qq/UploadFiles_7828/201611/2016110420035680.jpg"];
        @try {
            NSData *data = [[NSData alloc] initWithContentsOfURL:url];
            if (data) {
                rightData = data;
                dispatch_async(dispatch_get_main_queue(), ^{
                    weakSelf.rightImageView.image = [UIImage imageWithData:data];
                });
            }
        } @catch (NSException *exception) {
            NSLog(@"下载图片2出错啦");
        }
        NSLog(@"第二项任务完成");
    });

图片下载结果:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        dispatch_group_wait(disgroup, dispatch_time(DISPATCH_TIME_NOW, 30 * NSEC_PER_SEC));
        NSLog(@"dispatch_group_wait结束");
        if (leftData && rightData) {
            NSLog(@"图片下载成功");
        }
        else {
            NSLog(@"图片下载失败");
        }
    });

合成:

dispatch_group_notify(disgroup, disqueue, ^{
        NSLog(@"dispatch_group_notify执行");
        if (leftData && rightData) {
            CGSize size = CGSizeMake(0, weakSelf.lowerImageView.frame.size.height);
            size.width = size.height * 2;
            UIImage *image1 = [UIImage imageWithData:leftData];
            UIImage *image2 = [UIImage imageWithData:rightData];
            UIGraphicsBeginImageContext(size);
            CGFloat length = size.height;
            [image1 drawInRect:CGRectMake(0, 0, length, length)];
            [image2 drawInRect:CGRectMake(length, 0, length, length)];
            UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
            UIGraphicsEndImageContext();
            if (image) {
                dispatch_async(dispatch_get_main_queue(), ^{
                    weakSelf.lowerImageView.image = image;
                });
            }
            NSLog(@"图片合成结束");
        }
    });