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];
}
如何为这个循环设置进度 View ,我想为下载数据设置进度 View 。 以及进度标签(即 %)我想要百分比小数。
最佳答案
简单的解决方案是异步执行此操作,同时更新进度 View :
创建进度 View 并将其添加到您的 View
将您的代码分派(dispatch)到后台队列
每次下载完成后,将进度 View 的更新分派(dispatch)回主队列
在伪代码中,它看起来像
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];
});
}
});
还有一系列越来越优雅的方法:
使用并发队列(而不是上面那种串行下载图片的方式)来下载图片,速度会明显加快。我可能建议使用
5
的maxConcurrentCount
操作队列,以享受并发性,但请确保您没有超过 iOS 的并发请求数限制。使用基于
NSURLConnectionDataDelegate
的下载而不是NSData
方法initWithContentsOfURL
,后者可以在单个下载期间提供临时进度。参见 download manager或 download operation例如。使用 AFNetworking它还提供了基于下载进度 block 的接口(interface)。
上面,在第 1 点中,我建议您考虑使用并发队列,因此我决定对其进行基准测试。对我来说,下面的这个 GCD 实现比它后面的 NSOperationQueue
实现慢 3-4 倍。
这是 GCD 实现:
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);
});
对于这个 NSOperationQueue
实现:
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];
最重要的是,如果您使用 NSOperationQueue
(它不仅提供并发性,您也可以在 GCD 并发队列中执行此操作,而且还可以让您轻松控制并发操作的数量(您对于网络操作应限制为五个或更少)),您将享受显着的性能优势。
如我所建议的,更好的方法是使用 AFNetworking,在其中您不仅可以享受操作队列并发优势,还可以享受其他优势。
关于ios - 在循环中设置进度 View ,或者更新进度 View ,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/19834016/