iOS NSURLSession Download - ios

Question

I got this code to implement something which helps me downloading a file from a given URL.
-(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);
}
Second part:
-(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];
}
All of this code is in my Download.m
My download.h is:
#interface Download : NSObject
-(void) downloadFileWithProgress
#end
I really dont know how to get the download starting. In another class I created a button which should start the download:
-(IBAction)buttonStartDownload:(id)sender {
[Download downloadFileWithProgress];
}
The error is in the last line:
No known class method for selector 'downloadFileWithProgress'
But why?

Answer 1

The method '-(void) downloadFileWithProgress' is an instance method so you cant call this method by using class name 'Download'.
In order to call this method you need to create an instance of 'Download' class and call the method on that instance.

Answer 2

Method -(void)downloadFilwWithProgress in instance method...So to call that method
-(IBAction)buttonStartDownload:(id)sender {
Download *downldObj=[[Download alloc]init];
[downldObj downloadFileWithProgress];
}
If you write method +(void)downloadFilwWithProgress then you can call like this.[Download downloadFileWithProgress]