在iOS中使用afnetworking时图像下载进度条不顺畅

我目前正在使用afnetworking下载图像，但是第一次下载的进度条并不平滑，但是当我第二次运行此代码时，进度条是平滑的，这是我下载图像的代码

进度条的工作原理类似于向上，向下，而不是平滑，但当我第二次运行代码时，它工作起来很平滑

  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];

---

}

此代码来自2013年的一个答案。我建议

• 不要使用不推荐的

  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，但现在您可以使用

  NSProgress

  进行个别下载，这些下载是某个家长的子女

  NSProgress

  。您可以让您的

  UIProgressView

  观察这一点。最终的结果是，您只需更新子

  NSProgress

  实例，您的父进程视图就会自动更新

例如，假设我有一个名为

totalProgressView

的父级

UIProgressView

，我有一个它正在观察的

NSProgress

：

@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

在哪里

及

static const long kdefultimagesize=1000000；//如果服务器不提供totalBytesExpected，我们应该假设它是什么
@实现映像下载
-（id）initWithURL:（NSURL*）url文件名：（NSString*）文件名{
self=[super init]；
如果（自我）{
_url=url；
_进度=[NSProgress progress WITH TOTALLUNITCUNT:kDefaultImageSize]；
_filename=filename？：url.lastPathComponent；
}
回归自我；
}
-（void）写入的总字节更新程序：（int64_t）TotalBytesWrite totalBytesExpectedToWrite：（int64_t）totalBytesExpectedToWrite{
int64_t totalUnitCount=totalBytesExpectedToWrite；
if（totalBytesExpectedToWriteif（TotalBytesWrite请参见基本
NSURLSession
示例。请参见AFNetworking 3.2示例（注意，我没有将AFNetworking代码添加到我上传的项目中，因此您可能需要自己获取这些内容）。非常感谢您，先生
@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

- (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];
}

//  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

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