iOS NSURLSession 下载

Question

我得到这段代码来实现一些东西，它可以帮助我从给定的 URL 下载文件。

-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
{
    NSLog(@"Temporary File :%@\n", location);
    NSError *err = nil;
    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSString *docsDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];

    NSURL *docsDirURL = [NSURL fileURLWithPath:[docsDir stringByAppendingPathComponent:@"out1.zip"]];
    if ([fileManager moveItemAtURL:location
                             toURL:docsDirURL
                             error: &err])
    {
        NSLog(@"File is saved to =%@",docsDir);
    }
    else
    {
        NSLog(@"failed to move: %@",[err userInfo]);
    }

}

-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{
    //You can get progress here
    NSLog(@"Received: %lld bytes (Downloaded: %lld bytes)  Expected: %lld bytes.\n",
          bytesWritten, totalBytesWritten, totalBytesExpectedToWrite);
}

第二部分:

-(void) downloadFileWithProgress
{
    NSURL * url = [NSURL URLWithString:@"https://s3.amazonaws.com/hayageek/downloads/SimpleBackgroundFetch.zip"];
    NSURLSessionConfiguration *defaultConfigObject = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *defaultSession = [NSURLSession sessionWithConfiguration: defaultConfigObject delegate:self delegateQueue: [NSOperationQueue mainQueue]];

    NSURLSessionDownloadTask * downloadTask =[ defaultSession downloadTaskWithURL:url];
    [downloadTask resume];

}

所有这些代码都在我的 Download.m 中

我的download.h是:

@interface Download : NSObject
-(void) downloadFileWithProgress
@end

我真的不知道如何开始下载。在另一个类中，我创建了一个应该开始下载的按钮:

-(IBAction)buttonStartDownload:(id)sender {
[Download downloadFileWithProgress];
}

错误在最后一行:

No known class method for selector 'downloadFileWithProgress'

但为什么呢？

Answer 1

方法“-(void) downloadFileWithProgress”是一个实例方法，因此您不能使用类名“Download”调用此方法。

为了调用此方法，您需要创建“下载”类的实例并在该实例上调用该方法。