Ios 在循环中设置进度视图，或更新进度视图 for（int i=0；i

简单的解决方案是异步执行此操作，在执行时更新进度视图：

创建进度视图并将其添加到视图中

将代码分派到后台队列

每次下载完成后，将进度视图的更新发送回主队列

在伪代码中，这看起来像

for (int i=0; i<[array count]; i++)
{
    NSError *error;
    NSArray *ipaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *idocumentsDir = [ipaths objectAtIndex:0];
    NSString *idataPath = [idocumentsDir stringByAppendingPathComponent:@"File"];
    NSLog(@"idataPath:%@",idataPath);

    //Create folder here
    if (![[NSFileManager defaultManager] fileExistsAtPath:idataPath])
    {
        [[NSFileManager defaultManager] createDirectoryAtPath:idataPath withIntermediateDirectories:NO attributes:nil error:&error];
    }
    // Image Download here
    NSString *fileName = [idataPath stringByAppendingFormat:@".jpg"];
    NSLog(@"imagePathDOWNLOAD:%@",fileName);

    _imgData = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:[array objectAtIndex:i]]];
    [_imgData writeToFile:fileName atomically:YES];

    tempImg.image = [UIImage imageWithData:_imgData];   
}

为此

NSOperationQueue

实现：

UIProgressView *progressView = [[UIProgressView alloc] init];
// configure the progress view and add it to your UI

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    for (int i=0; i<[array count]; i++)
    {
        NSError *error;
        NSArray *ipaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *idocumentsDir = [ipaths objectAtIndex:0];
        NSString *idataPath = [idocumentsDir stringByAppendingPathComponent:@"File"];
        NSLog(@"idataPath:%@",idataPath);

        //Create folder here
        if (![[NSFileManager defaultManager] fileExistsAtPath:idataPath])
        {
            [[NSFileManager defaultManager] createDirectoryAtPath:idataPath withIntermediateDirectories:NO attributes:nil error:&error];
        }
        // Image Download here
        NSString *fileName = [idataPath stringByAppendingFormat:@".jpg"];
        NSLog(@"imagePathDOWNLOAD:%@",fileName);

        _imgData = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:[array objectAtIndex:i]]];
        [_imgData writeToFile:fileName atomically:YES];

        // now dispatch any UI updates back to the main queue
        dispatch_async(dispatch_get_main_queue(), ^{

            [progressView setProgress: (CGFloat) (i + 1.0) / [array count] animated:YES];
            tempImg.image = [UIImage imageWithData:_imgData];
        });
    }
});

CFAbsoluteTime start = CFAbsoluteTimeGetCurrent();

UIProgressView *progressView = [self addProgressView];

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

    NSInteger downloadSuccessCount = 0;
    NSInteger downloadFailureCount = 0;

    NSString *idataPath = [self createDownloadPath];

    for (int i = 0; i < [array count]; i++)
    {
        // Image Download here
        NSString *filename = [self pathForItem:i array:array folder:idataPath];
        NSURL *url = [self urlForItem:i array:array];
        NSData *data = [[NSData alloc] initWithContentsOfURL:url];
        UIImage *image = nil;
        if (data)
            image = [UIImage imageWithData:data];
        if (image) {
            downloadSuccessCount++;
            [data writeToFile:filename atomically:YES];
        } else {
            downloadFailureCount++;
        }

        // now dispatch any UI updates back to the main queue
        dispatch_async(dispatch_get_main_queue(), ^{

            [progressView setProgress: (CGFloat) (downloadSuccessCount + downloadFailureCount) / [array count] animated:YES];

            // update the image in the UI if you want

            [UIView transitionWithView:self.imageView duration:0.25 options:UIViewAnimationOptionTransitionCrossDissolve animations:^{
                tempImg.image = image;
            } completion:nil];
        });
    }

    NSLog(@"Completed in %.1f seconds", CFAbsoluteTimeGetCurrent() - start);
});

CFAbsoluteTime start=CFAbsoluteTimeGetCurrent（）；
UIProgressView*progressView=[self addProgressView]；
NSOperationQueue*队列=[[NSOperationQueue alloc]init]；
queue.maxConcurrentOperationCount=5；
NSString*idataPath=[self-createDownloadPath]；
self.downloadsuccescount=0；
self.downloadFailureCount=0；
NSOperation*completionOperation=[NSBlockOperation blockOperationWithBlock:^{
NSLog（@“在%.1f秒内完成”，CFAbsoluteTimeGetCurrent（）-开始）；
}];
对于（int i=0；i<[数组计数]；i++）
{
NSOperation*操作=[NSBlockOperation blockOperationWithBlock:^{
//图片下载
NSString*filename=[self-pathForItem:i数组：数组文件夹：idataPath]；
NSURL*url=[self-urlForItem:i数组：数组]；
NSData*data=[NSData dataWithContentsOfURL:url]；
UIImage*image=nil；
如果（数据）
image=[UIImage-imageWithData:data]；
如果（图像）
[数据写入文件：文件名原子：是]；
//现在将所有UI更新发送回主队列
[[NSOperationQueue mainQueue]添加操作与块：^{
如果（图像）{
self.downloadsuccescount++；
//如果需要，可以在UI中更新图像，尽管这样会减慢速度
[UIView转换WithView:self.imageView持续时间：0.25选项：UIView动画选项转换交叉溶解动画：^{
tempImg.image=图像；
}完成：无]；
}
其他的
self.downloadFailureCount++；
[progressView setProgress:（CGFloat）（self.downloadSuccessCount+self.downloadFailureCount）/[array count]动画：是]；
}];
}];
[队列添加操作：操作]；
[completionOperation addDependency:operation]；
}
[队列添加操作：完成操作]；

总之，如果您使用

NSOperationQueue

（它不仅可以提供并发性，您也可以在GCD并发队列中实现并发性，还可以让您轻松控制并发操作的数量（对于网络操作，您应该将并发操作的数量限制在五个或更少），您将享受到显著的性能优势

---

正如我所建议的那样，更好的做法是使用AFNetworking，在这种网络中，您不仅可以享受操作队列并发性的好处，还可以享受其他好处。

并设置进度标签（即%）@emotality当然可以，但仅当您按顺序进行操作时才可以。但如果您使用的是并发、异步请求（你应该这样做，因为它要快得多），您不能仅使用

for

循环的

i

变量来更新进度视图。对于并发请求，您无法保证这些请求将完成的顺序。相反，您必须拥有一些其他类属性来跟踪已完成下载的数量，并在更新t时使用该计数器他是进度视图。Lol对不起，我的意思是为那些搜索我搜索的内容的人。我没有阅读答案或问题，但上面的代码是我搜索的内容。如果其他人也搜索了，他们会帮助他们。谢谢回答！）

CFAbsoluteTime start = CFAbsoluteTimeGetCurrent();

UIProgressView *progressView = [self addProgressView];

NSOperationQueue *queue = [[NSOperationQueue alloc] init];
queue.maxConcurrentOperationCount = 5;

NSString *idataPath = [self createDownloadPath];
self.downloadSuccessCount = 0;
self.downloadFailureCount = 0;

NSOperation *completionOperation = [NSBlockOperation blockOperationWithBlock:^{
    NSLog(@"Completed in %.1f seconds", CFAbsoluteTimeGetCurrent() - start);
}];

for (int i = 0; i < [array count]; i++)
{
    NSOperation *operation = [NSBlockOperation blockOperationWithBlock:^{
        // Image Download here
        NSString *filename = [self pathForItem:i array:array folder:idataPath];
        NSURL *url = [self urlForItem:i array:array];
        NSData *data = [NSData dataWithContentsOfURL:url];
        UIImage *image = nil;
        if (data)
            image = [UIImage imageWithData:data];
        if (image)
            [data writeToFile:filename atomically:YES];

        // now dispatch any UI updates back to the main queue
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{

            if (image) {
                self.downloadSuccessCount++;

                // update the image in the UI if you want, though this slows it down

                [UIView transitionWithView:self.imageView duration:0.25 options:UIViewAnimationOptionTransitionCrossDissolve animations:^{
                    tempImg.image = image;
                } completion:nil];
            }
            else
                self.downloadFailureCount++;

            [progressView setProgress: (CGFloat) (self.downloadSuccessCount + self.downloadFailureCount) / [array count] animated:YES];
        }];
    }];

    [queue addOperation:operation];
    [completionOperation addDependency:operation];
}

[queue addOperation:completionOperation];

[progressView setProgress: (CGFloat) (i + 1.0) / [array count] animated:YES];
self.progressLabel.text = [NSString stringWithFormat:@"%.0f",self.progressView.progress*100];