我有一个包含进度条的UIView。我想做的很简单，我有一个按钮，用户点击该按钮，应用程序下载文件并显示进度条中的进度。我可以在用户第一次点击下载按钮时执行此操作。但是，当用户再次单击第二次下载时，不会调用NSURLSession个委托。
我的UIView .m
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
[self configure];
}
return self;
}
- (id)initWithCoder:(NSCoder *)aDecoder
{
self = [super initWithCoder:aDecoder];
if (self) {
[self configure];
}
return self;
}
-(void)configure
{
[self createSpinner];
[self createProgressBar];
NSArray *URLs = [[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask];
self.docDirectoryURL = [URLs objectAtIndex:0];
NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:@"com.tinkytickles"];
sessionConfiguration.HTTPMaximumConnectionsPerHost = 1;
self.session = [NSURLSession sessionWithConfiguration:sessionConfiguration
delegate:self
delegateQueue:nil];
}
-(void)createSpinner
{
[self setBackgroundColor:[UIColor colorWithWhite:1.0f alpha:0.5f]];
spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
[self addSubview:spinner];
[spinner setColor:original_new_dark_grey];
[spinner setUserInteractionEnabled:NO];
[spinner setCenter:CGPointMake([[UIScreen mainScreen] bounds].size.width/2, [[UIScreen mainScreen] bounds].size.height/2)];
[spinner setFrame:CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, [UIScreen mainScreen].bounds.size.height)];
[spinner startAnimating];
}
-(void)createProgressBar
{
self.progressBar = [[TYMProgressBarView alloc] initWithFrame:CGRectMake(0, 0, 280, 15)];
[self.progressBar setBarBackgroundColor:[UIColor whiteColor]];
[self.progressBar setBarBorderColor:original_new_dark_grey];
[self.progressBar setBarFillColor:original_new_dark_grey];
[self.progressBar setBarBorderWidth:1.0f];
[self addSubview:self.progressBar];
[self.progressBar setCenter:CGPointMake([[UIScreen mainScreen] bounds].size.width/2, [[UIScreen mainScreen] bounds].size.height/2)];
[self.progressBar setHidden:YES];
self.label = [[UILabel alloc] initWithFrame:CGRectMake(self.progressBar.frame.origin.x, self.progressBar.frame.origin.y - 30, self.progressBar.frame.size.width, 25)];
[self.label setText:NSLocalizedString(locDownloading, nil)];
[self.label setTextAlignment:NSTextAlignmentCenter];
[self.label setTextColor:original_new_dark_grey];
[self.label setFont:quicksand_14];
[self addSubview:self.label];
[self.label setHidden:YES];
}
-(void)showProgressBarWithProgress:(CGFloat)progress withText:(NSString *)text
{
[spinner setHidden:YES];
[self.label setText:[NSString stringWithFormat:NSLocalizedString(locDownloadingAt, nil), text]];
[self.label setHidden:NO];
[self.progressBar setHidden:NO];
[self.progressBar setProgress:progress];
}
-(void)stopAnimating
{
[spinner stopAnimating];
}
-(void)startDownloadingURL:(PromoterDownloadInfo *)downloadInfo
{
info = downloadInfo;
if (!info.isDownloading)
{
if (info.taskIdentifier == -1)
{
info.downloadTask = [self.session downloadTaskWithURL:[NSURL URLWithString:info.downloadSource]];
info.taskIdentifier = info.downloadTask.taskIdentifier;
[info.downloadTask resume];
}
else
{
info.downloadTask = [self.session downloadTaskWithResumeData:info.taskResumeData];
[info.downloadTask resume];
info.taskIdentifier = info.downloadTask.taskIdentifier;
}
}
else
{
[info.downloadTask cancelByProducingResumeData:^(NSData *resumeData) {
if (resumeData != nil) {
info.taskResumeData = [[NSData alloc] initWithData:resumeData];
}
}];
}
info.isDownloading = !info.isDownloading;
}
-(void)stopDownload:(PromoterDownloadInfo *)downloadInfo
{
if (!info.isDownloading)
{
if (info.taskIdentifier == -1)
{
info.downloadTask = [self.session downloadTaskWithURL:[NSURL URLWithString:info.downloadSource]];
}
else
{
info.downloadTask = [self.session downloadTaskWithResumeData:info.taskResumeData];
}
info.taskIdentifier = info.downloadTask.taskIdentifier;
[info.downloadTask resume];
info.isDownloading = YES;
}
[self stopAnimating];
[self removeFromSuperview];
}
#pragma mark - NSURLSession Delegate method implementation
-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
{
NSError *error;
NSFileManager *fileManager = [NSFileManager defaultManager];
NSString *destinationFilename = downloadTask.originalRequest.URL.lastPathComponent;
NSURL *destinationURL = [self.docDirectoryURL URLByAppendingPathComponent:destinationFilename];
if ([fileManager fileExistsAtPath:[destinationURL path]]) {
[fileManager removeItemAtURL:destinationURL error:nil];
}
BOOL success = [fileManager copyItemAtURL:location
toURL:destinationURL
error:&error];
if (success) {
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
[self stopAnimating];
[self removeFromSuperview];
}];
}
else
{
NSLog(@"Unable to copy temp file. Error: %@", [error localizedDescription]);
}
}
-(void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error{
if (error != nil) {
NSLog(@"Download completed with error: %@", [error localizedDescription]);
}
else{
NSLog(@"Download finished successfully.");
}
}
-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{
if (totalBytesExpectedToWrite == NSURLSessionTransferSizeUnknown) {
NSLog(@"Unknown transfer size");
}
else
{
dispatch_async(dispatch_get_main_queue(), ^{
info.downloadProgress = (double)totalBytesWritten / (double)totalBytesExpectedToWrite;
[self showProgressBarWithProgress:info.downloadProgress withText:info.fileTitle];
});
}
}
-(void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session
{
AppDelegate *appDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;
// Check if all download tasks have been finished.
[self.session getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) {
if ([downloadTasks count] == 0) {
if (appDelegate.backgroundTransferCompletionHandler != nil) {
// Copy locally the completion handler.
void(^completionHandler)() = appDelegate.backgroundTransferCompletionHandler;
// Make nil the backgroundTransferCompletionHandler.
appDelegate.backgroundTransferCompletionHandler = nil;
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
// Call the completion handler to tell the system that there are no other background transfers.
completionHandler();
// Show a local notification when all downloads are over.
UILocalNotification *localNotification = [[UILocalNotification alloc] init];
localNotification.alertBody = NSLocalizedString(locDownloadComplete, nil);
[[UIApplication sharedApplication] presentLocalNotificationNow:localNotification];
}];
}
}
}];
}
我像这样使用这个UIView：
PromoterDownloadInfo *info = [[PromoterDownloadInfo alloc] initWithFileTitle:self.title andDownloadSource:@"https://www.mywebsite.com/file.zip"];
PromotersDownloadView *downloadView = [[PromotersDownloadView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
[self.navigationController.view addSubview:downloadView];
[downloadView startDownloadingURL:info];
我第一次点击下载按钮时效果很好。第二次调用NSURLSession didCompleteWithError方法。这是我第二次从日志中获得的内容：
2016-05-12 00:50:47.440 APP[32990:1230071] A background URLSession with identifier com.app already exists!
2016-05-12 00:50:50.614 APP[32990:1230386] Download finished successfully.
我做错了什么？我尝试只创建一次NSURLSessionConfiguration，但这样就不会调用任何委托方法。我该怎么办？
答案 0 :(得分：1)
你说：
我第一次点击下载按钮时效果很好。 ......这是我第二次从日志中获得的信息：
2016-05-12 00:50:47.440 APP[32990:1230071] A background URLSession with identifier com.app already exists!<br />
该错误指出您只想为给定标识符实例化一个背景NSURLSession（并且您通常只需要/想要一个后台会话）。如果您要实例化多个，那么您将为它们提供唯一标识符，但处理后台会话非常复杂，而不必多次会话。我建议你只想要一个后台会话。
你说：
我尝试只创建一次
NSURLSessionConfiguration，但这样就不会调用任何委托方法。
是的，您应该有一个会话配置。而且，同样重要的是，只有一个后台会话对象。
我怀疑您的委托对象无法跟踪应更新哪个视图存在问题。或者您可能丢失了对会话对象的引用，并且您的引用为nil。这可能是几件不同的事情，如果不了解你是如何做到这一点的话，很难知道。
我建议将此会话配置代码移出视图，并提供一些可以在任何地方引用的共享实例（例如，单例工作正常，因此您可以从首次需要的任何地方实例化它，无论是从视图还是来自app delegate的handleEventsForBackgroundURLSession方法。）
唯一的挑战是如何跟踪哪些视图跟踪哪些网络请求。您是否希望拥有一个能够跟踪所有未完成请求的视图，无论该视图何时被实例化？如果是这样，您可以使用NSNotificationCenter通知（这样，任何想要通知进度更新的视图都可以观察您的自定义通知）。或者给定视图是否只关心您从该视图发起的请求？在这种情况下，您可能会维护字典，以映射taskIdentifier值，以便视图或对象需要了解状态更新（您可以使用哪种方式）您的会话对象会跟踪哪些视图关注哪些任务）。这取决于您的应用程序的要求。