ProgressView for Downloading some files in Object-C

问题

my problem is this:

I want to show ProgressView for files downloading.For some reason the ProgressView gradually rises, showing how much file is already downloaded , and just immediately fills up when files are still not downloaded! What do I need to fix or how to implement it?

Here is my source code:

- (IBAction)download:(id)sender {


    // Determile cache file path
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

    progressSlider.progress = 0.0;

    for (i=0;i<=7;i++) {

        //Updating progressView and progressLabel
        progressLabel.text = [NSString stringWithFormat:@"Загружено: %d из 7",i];
        progressView.progress = (float)i/(float)7;

        NSString *filePath = [NSString stringWithFormat:@"%@/avto-0-%d.html", [paths objectAtIndex:0],i];

        // Download and write to file
        NSString *mustUrl = [NSString stringWithFormat:@"http://www.mosgortrans.org/pass3/shedule.php?type=avto&%@", [listOfAvtoUrl objectAtIndex:i]];
        NSURL *url = [NSURL URLWithString:mustUrl];
        NSData *urlData = [NSData dataWithContentsOfURL:url];


        [urlData writeToFile:filePath atomically:YES];
    }
 }

回答1:

I think that it is related to threads and how the main thread will refresh the view.

Two cases can occur:

You are on the main thread when calling this method

In such case, you do not allow the main thread to execute refresh routines. Move all this download to a background queue using GCD, and call back the main thread like explained in pt.2.

To put everything in a background queue, you could call:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^ {
        // your download code goes here


    });

Or, You are already on the background thread, then use the following lines to call back to the main thread:

dispatch_async(dispatch_get_main_queue(), ^ {
            progressView.progress = (float)i/(float)7;
        });

Final answer:

- (IBAction)download:(id)sender {

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^ {
    // Determile cache file path
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

    progressSlider.progress = 0.0;

    for (i=0;i<=7;i++) {

        //Updating progressView and progressLabel
        progressLabel.text = [NSString stringWithFormat:@"Загружено: %d из 7",i];
dispatch_async(dispatch_get_main_queue(), ^ {
        progressView.progress = (float)i/(float)7;
});

        NSString *filePath = [NSString stringWithFormat:@"%@/avto-0-%d.html", [paths objectAtIndex:0],i];

        // Download and write to file
        NSString *mustUrl = [NSString stringWithFormat:@"http://www.mosgortrans.org/pass3/shedule.php?type=avto&%@", [listOfAvtoUrl objectAtIndex:i]];
        NSURL *url = [NSURL URLWithString:mustUrl];
        NSData *urlData = [NSData dataWithContentsOfURL:url];


        [urlData writeToFile:filePath atomically:YES];
    }
});
 }

来源：https://stackoverflow.com/questions/13512846/progressview-for-downloading-some-files-in-object-c