Get download progress from different ViewController

问题

I have a VideoListController. It has list of videos with download button. When I press the download button, the control is transferred to DetailViewController. In DetailViewController, I am using AFNetworking to download file.

If I go back to VideoListController from DetailViewController. How can I know progress of download or when download gets completed from VideoListController. I want to know this because based upon that I will reload the list to show play button instead of download.

回答1:

I think that the best solution for your problem would be to create a custom delegate protocol that the DetailViewController and the VideoListController can use to communicate with each other. Check this post for additional information How to use custom delegates in Objective-C

In a nutshell the strategy is the following: 1. The DetailViewController defines a delegate protocol that it uses to pass events to its delegate 2. The VideoListController becomes the delegate to that it knows whenever an upload has progressed or been completed 3. The VideoListController keeps track of which DetailViewControllers have completed the download

Here is come code: DetailViewController.h:

@class DetailViewController;
@protocol Delegate <NSObject>
- (void) detailViewController: (DetailViewController *) theDetailViewController didFinishDownloadingVideoWithResults:(BOOL)successful;
@end

@property (nonatomic, weak) id<DetailViewController> delegate;

DetailViewController.m: Whenever a download is complete do the following:

if ([[self delegate] respondsToSelector:@selector(detailViewController:didFinishDownloadingVideoWithResults:)]){
   [[self delegate] detailViewController:self didFinishDownloadingVideoWithResults:YES];
}

Now, in the VideoListController.m make sure you establish yourself as the delegate of the DetailViewController.

[theDetailViewController setDelegate:self];

And implement the delegate method. You can for instance have a dictionary that defines which DetailViewControllers have completed the download:

   - (void) detailViewController: (DetailViewController *) theDetailViewController didFinishDownloadingVideoWithResults:(BOOL)successful{
      detailViewControllersDownloadInformation[theDetailViewController] = @(successful);
}

Now, whenever you need to check if a DetailViewController did indeed complete a download, all you have to do is check that dictionary

if (detailViewControllersDownloadInformation[theDetailViewController] && detailViewControllersDownloadInformation[theDetailViewController] == @(YES)){
    // Did download a video
}

Keep in mind that the solution I provide will only let you know if the download has been completed. If you also want to keep track of the progress you need to pass that as an additional parameter in the delegate. We are also assuming that you keep all of the DetailViewControllers in memory. If you release and reuse them you will need to keep track of which element was downloaded in a different data structure.

回答2:

I got it working using NSNotificationCenter. In viewDidLoad of DetailViewController, I added this

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(movieDownloadDidFinish)
                                             name:@"MovieDownloadDidFinishNotification"
                                           object:nil];

When download gets complete. I call this:

[[NSNotificationCenter defaultCenter] postNotificationName:@"MovieDownloadDidFinishNotification" object:self];

I remove the observer from DetailViewController when when backbutton in navigation controller is clicked

[[NSNotificationCenter defaultCenter] removeObserver:self name:@"MovieDownloadDidFinishNotification" object:nil];

And added method in DetailViewController that is called when download gets completed.

-(void) movieDownloadDidFinish {
    NSLog(@"MovieDownloadDidFinish on DetailViewController");
}

Now in viewDidAppear of VideoListController, I added the observer

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(movieDownloadDidFinish)
                                             name:@"MovieDownloadDidFinishNotification"
                                           object:nil];

And in viewDidDisappear Of VideoListController, I remove the observer

[[NSNotificationCenter defaultCenter] removeObserver:self name:@"MovieDownloadDidFinishNotification" object:nil];

And added method in VideoListController that is called when download gets completed.

-(void) movieDownloadDidFinish {
    NSLog(@"MovieDownloadDidFinish On VideoListController");
}

In this way, when DetailViewController is visible, the method movieDownloadDidFinish of DetailViewController is called and similarly movieDownloadDidFinish of VideoListController is called when VideoListController is visible.

来源：https://stackoverflow.com/questions/16251054/get-download-progress-from-different-viewcontroller