在 iOS 中使用 afnetworking 的图像下载进度条不流畅

Question

我目前正在使用afnetworking下载图像，但是第一次进度条不流畅，但是当我第二次运行此代码时，进度条是流畅的，这是我下载图像的代码。

进度条的工作方式像上升，下降而不是平滑，但是当我第二次运行代码时它工作顺利

  progressBar.progress = 0.0;

self.imageDownloads=[[NSMutableArray alloc]init];

[self.imageDownloads addObject:[[ImageDownload alloc] initWithURL:[NSURL URLWithString:@""]];

 for (int i=0; i < self.imageDownloads.count; i++)
{
    ImageDownload *imageDownload = self.imageDownloads[i];
    imageDownload.filename = [NSString stringWithFormat:@"MyImage%d",i];
    [self downloadImageFromURL:imageDownload];
}

Here is my code to download images




- (void)downloadImageFromURL:(ImageDownload *)imageDownload
{

 NSString *docsPath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0];
NSString *filePath = [docsPath stringByAppendingPathComponent:imageDownload.filename];
NSURLRequest *request = [NSURLRequest requestWithURL:imageDownload.url];
AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
[operation setDownloadProgressBlock:^(NSUInteger bytesRead, long long totalBytesRead, long long totalBytesExpectedToRead) {
    imageDownload.totalBytesRead = totalBytesRead;
    imageDownload.totalBytesExpected = totalBytesExpectedToRead;
    [self updateProgressView];
}];
[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
    NSAssert([responseObject isKindOfClass:[NSData class]], @"expected NSData");
    NSData *responseData = responseObject;
    [responseData writeToFile:filePath atomically:YES];

    // Because totalBytesExpected is not entirely reliable during the download,
    // now that we're done, let's retroactively say that total bytes expected
    // was the same as what we received.

    imageDownload.totalBytesExpected = imageDownload.totalBytesRead;
    [self updateProgressView];

    NSLog(@"finished %@", imageDownload.filename);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
    NSLog(@"error %@", imageDownload.filename);
}];
[operation start];

}

 - (void)updateProgressView
{
double totalTotalBytesRead = 0;
double totalTotalBytesExpected = 0;

for (ImageDownload *imageDownload in self.imageDownloads)
{
    // note,
    //    (a) totalBytesExpected is not always reliable;
    //    (b) sometimes it's not present at all, and is negative
    //
    // So, when estimating % complete, we'll have to fudge
    // it a little if we don't have total bytes expected

    if (imageDownload.totalBytesExpected >= 0)
    {
        totalTotalBytesRead += imageDownload.totalBytesRead;
        totalTotalBytesExpected += imageDownload.totalBytesExpected;
    }
    else
    {
        totalTotalBytesRead += imageDownload.totalBytesRead;
        totalTotalBytesExpected += (imageDownload.totalBytesRead > kDefaultImageSize ? imageDownload.totalBytesRead + kDefaultImageSize : kDefaultImageSize);
    }
}

if (totalTotalBytesExpected > 0)
    [progressBar setProgress:totalTotalBytesRead / totalTotalBytesExpected animated:YES];
else
    [progressBar setProgress:0.0 animated:NO];

}

Answer 1

此代码来自 2013 年的答案。我建议

• 不要使用已弃用的AFHTTPRequestOperation，而是使用NSURLSession 下载基于任务的解决方案。如果你想使用 AFNetworking，他们有一种机制可以做到这一点。

• 不要自己更新/计算百分比，而是现在你会使用 NSProgress 来进行个别下载，这些下载是某些父级 NSProgress 的子级。你可以让你的UIProgressView 观察。最终效果是您最终只更新了子 NSProgress 实例，并且您的父级的进度视图会自动更新。

例如，假设我有一个名为 totalProgressView 的父 UIProgressView 并且我有一个 NSProgress 正在观察：

@interface ViewController () <UITableViewDataSource>

@property (nonatomic, strong) NSProgress *totalProgress;
@property (nonatomic, strong) NSMutableArray <ImageDownload *> *imageDownloads;

@property (nonatomic, weak) IBOutlet UIProgressView *totalProgressView;
@property (nonatomic, weak) IBOutlet UITableView *tableView;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    self.totalProgress = [[NSProgress alloc] init];
    self.totalProgressView.observedProgress = self.totalProgress;
    self.tableView.estimatedRowHeight = 50;
    self.tableView.rowHeight = UITableViewAutomaticDimension;

    self.imageDownloads = [NSMutableArray array];
}

...

@end

然后开始下载，我创建了一系列图像下载，将它们各自的 NSProgress 实例添加为上述 totalProgress 的子实例：

- (IBAction)didTapStartDownloadsButton {
    NSArray <NSString *> *urlStrings = ...

    NSURL *caches = [[[NSFileManager defaultManager] URLForDirectory:NSCachesDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:true error:nil] URLByAppendingPathComponent:@"images"];
    AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];

    self.totalProgress.totalUnitCount = urlStrings.count;
    for (NSInteger i = 0; i < urlStrings.count; i++) {
        NSURL *url = [NSURL URLWithString:urlStrings[i]];
        NSString *filename = [NSString stringWithFormat:@"image%ld.%@", (long)i, url.pathExtension];
        ImageDownload *imageDownload = [[ImageDownload alloc] initWithURL:url filename:filename];
        [self.imageDownloads addObject:imageDownload];
        [self.totalProgress addChild:imageDownload.progress withPendingUnitCount:1];

        NSURLRequest *request = [NSURLRequest requestWithURL:url];
        NSURLSessionDownloadTask *task = [manager downloadTaskWithRequest:request progress:^(NSProgress * _Nonnull downloadProgress) {
            [imageDownload updateProgressForTotalBytesWritten:downloadProgress.completedUnitCount
                                    totalBytesExpectedToWrite:downloadProgress.totalUnitCount];
        } destination:^NSURL * _Nonnull(NSURL * _Nonnull targetPath, NSURLResponse * _Nonnull response) {
            return [caches URLByAppendingPathComponent:filename];
        } completionHandler:^(NSURLResponse * _Nonnull response, NSURL * _Nullable filePath, NSError * _Nullable error) {
            //do whatever you want here
        }];
        [task resume];
    }

    [self.tableView reloadData];
}

在哪里

//  ImageDownload.h

@import Foundation;

NS_ASSUME_NONNULL_BEGIN

@interface ImageDownload : NSObject

@property (nonatomic, strong) NSURL *url;
@property (nonatomic, strong) NSString *filename;
@property (nonatomic) NSProgress *progress;
@property (nonatomic) NSUInteger taskIdentifier;

- (id)initWithURL:(NSURL *)url
         filename:(NSString * _Nullable)filename;

/**
 Update NSProgress.

 @param totalBytesWritten Total number of bytes received thus far.
 @param totalBytesExpectedToWrite Total number of bytes expected (may be -1 if unknown).
 */

- (void)updateProgressForTotalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite;

@end

NS_ASSUME_NONNULL_END

和

static const long long kDefaultImageSize = 1000000; // what should we assume for totalBytesExpected if server doesn't provide it

@implementation ImageDownload

- (id)initWithURL:(NSURL *)url filename:(NSString *)filename {
    self = [super init];
    if (self) {
        _url = url;
        _progress = [NSProgress progressWithTotalUnitCount:kDefaultImageSize];
        _filename = filename ?: url.lastPathComponent;
    }
    return self;
}

- (void)updateProgressForTotalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite {
    int64_t totalUnitCount = totalBytesExpectedToWrite;

    if (totalBytesExpectedToWrite < totalBytesWritten) {
        if (totalBytesWritten <= 0) {
            totalUnitCount = kDefaultImageSize;
        } else {
            double written = (double)totalBytesWritten;
            double percent = tanh(written / (double)kDefaultImageSize);
            totalUnitCount = written / percent;
        }
    }

    dispatch_async(dispatch_get_main_queue(), ^{
        self.progress.totalUnitCount = totalUnitCount;
        self.progress.completedUnitCount = totalBytesWritten;
    });
}

@end

这会为各个下载生成单独的进度条，并且与 totalProgress 关联的进度条会自动为您更新，从而产生：

现在，很明显，您既不需要孩子UIProgressView 也不需要父母，所以这取决于您。但这个想法是

• 设置NSProgress的层次结构；
• 告诉UIProgressView观察你想要的任何NSProgress；和
• 只需让您的下载更新子 NSProgress 值，其余的将自动为您完成。