I'm developing an app which handles some downloads in the background. I move the file to the documents directory and save it under the original name (using downloadTask.originalRequest?.URL!.pathExtension). So far so good.
Using
URLSession(_:downloadTask:didWriteData:totalBytesWritten:totalBytesExpectedToWrite:)
I can print out the progress in the console while downloading. But this doesn't help me if I'm using the App on the phone. What I'm expecting to do is to call a function to update a progress bar from here within my View that was initialising the download. But I have no idea how to call it.
Does anybody know how I can find out from which UIViewController (actually most of the time it will be a TableCellViewController) I started the download and how to send the progress to a function of that ViewController?
I 'd like to tell you a good tutorial about this question. NSURLSession Tutorial
Delegates are often used in the following situations
When a class needs to communicate some information to another class
When a class wants to allow another class to customize it
The classes don't need to know anything about each other beforehand except that the delegate class conforms to the required protocol.
I the following article you can see how to create a delegate in objective-C and Swift 2.0.
How do I create delegates in Objective-C?
Related
Background: In order to make web requests to an API endpoint, I need to scrape a website and retrieve a token every 25-30 seconds. I'm doing this with a WKWebView and injecting some custom JavaScript using WKUserScript to retrieve AJAX response headers containing the token. Please focus on the question specifically and not on this background information - I'm attempting this entirely for my own educational purposes.
Goal
I will have different 'model' classes, or even just other UIViewControllers, that may need to call the shared UIViewController to retrieve this token to make an authenticated request.
Maybe I might abstract this into one "Sdk" class. Regardless, this 'model' SDK class could be instantiated and used by any other ViewController.
More info
I would like to be able to call the UIViewController of the WKWebView and retrieve some data. Unless I re-create it every 25 seconds, I need to run it in the background or share it. I would like to be able to run a UIViewController 'in the background' and receive some information from it once WKWebView has done it's thing.
I know there are multiple ways of communicating with another ViewController including delegation and segueing. However, I'm not sure that these help me keep the view containing the WKWebView existing in the background so I can call it's ViewController and have it re-perform the scrape. Delegation may work for normal code, but what about one that must have the view existing? Would I have to re-create this WKWebView dynamically each time a different model, or view controller, were to try and get this token?
One post suggests utilising ContainerViewControllers. From this, I gather that in the 'master' ViewController (the one containing the other ones), I could place the hidden WKWebView to do it's thing and communicate to the child view controllers that way via delegation.
Another post suggests using AppDelegate and making it a shared service. I'm completely against using a Singleton as it is widely considered an anti-pattern. There must be another way, even if a little more complex, that helps me do what I want without resorting to this 'cheat'.
This post talks about communicating between multiple ViewControllers, but I can't figure out how this would be useful when something needs to stay running and executing things.
How about any other ways to do this? Run something in a background thread with a strong pointer so it doesn't get discarded? I'm using Xcode 9.2, Swift 4, and iOS 11. As I'm very new to iOS programming, any small code examples on this would be appreciated.
Unfortunately, WKWebView must be in the view hierarchy to use it. You must have added it as a sub view of an on-screen view controller.
This was fine for me. I added this off-screen so it was not visible. Hidden attribute might have worked as well. Either way you must call addSubview with it to make it work.
There are some other questions and answers here which verify this.
Here is a way if you don't wish to use a singleton.
1- In the DidFinishlaunchingWithOptions, Make a timer that runs in the background and call a method inside the app delegate Called FetchNewToken.
2- In FetchNewToken, make the call needed and retrieve the new token (you can use alamofire or any 3rd library to make the call easier for you).
Up on successfully retrieving the token, save it in NSUserDefaults under the name upToDateToken
You can access this token anywhere from the application using NSUserDefaults and it will always be up to date.
In my swift app, during the initialization and load process I need to check CoreData for the availability of some records and further more make some bluetooth connections before display to the user.
Is there a recommendation on how to do this? Should I write this code directly in the AppDelegate or should I write it in a different Swift class and then invoke from the AppDelegate?
I am new to Swift so your suggestions are appreciated.
You Can do all this stuff in your View Controller i.e. your rootViewController by showing loader on screen to user and Checking the records in core data if present ,then retrieve them.
Don't be Confuse , just create a function checkRecords in appDelegate and put your code inside it and Call this function.
I am trying to read CoreData out of an iMessage Extension (MSMessagesAppViewController) but as there is no AppDelegate there is also no managedContext.
Has anybody an idea if that is possible?
Is it possible to "instantiate the AppDelegate" of my App or something like that?
Update: How to access core data within an app and an extension: The solution for this is to use AppGroup container.
Using Core Data has nothing to do with whether there is an application delegate. They are two separate things. You can put them together but neither Core Data nor the application delegate requires that. It's not even very good design to do so. The app delegate's job is to respond to app life-cycle events like launching, going into the background, etc, and it's bad design to also mix in the separate job of managing the app's data.
If you create a new project in Xcode and check the "use Core Data" box, Xcode will include methods in the app delegate class to set up Core Data for the app. But that code can go in any class. There's nothing special about the app delegate that requires that code to be in that class. Just because Xcode puts that code in that class doesn't mean that it's necessary to do it that way. If you need to use Core Data in an app extension, that's what you'll do.
One common approach is to create a new class to manage Core Data. Put all your Core Data stack management code there, instead of in the app delegate. The app delegate might create an instance of this class in your app. In an app extension, the class can be instantiated wherever it's needed for the type of extension.
I have an app that fetches data from a server using NSURLSessionDataTask. As of right now I am starting my HTTP GET Request in the init method of the UIViewController that displays the data. Is this the best/smartest place to kick off an HTTP request? If not, where should I do it?
I'm asking this question because when I exit my app and it goes into the background (and is not killed) and then re-open my application, the HTTP request is not fired off (because it is in the UIViewControllers init method) and the data being displayed is not up to date with what's on the server. I've tried putting it in viewDidLoad but this method is not called upon entering the foreground, neither is viewWillAppear nor viewDidAppear.
Should I be doing all of my HTTP requests in one of the UIApplications life cycle methods in my appDelegate?
In short, where is the best place to make HTTP requests in iOS?
Thank you, I can post code or explain more if needed.
first off, this is a huge question and probably impossible to answer fully here, but hopefully I can point you in the right direction so you can learn how to fish. :)
To stick to the Model-View-Controller paradigm, you will want to create a separate object for making your HTTP requests. An HTTP request would be considered part of your model. The benefit of this is being able to use your model in other iOS apps you create, for example.
As for where to put all of this stuff and what's the best design.... One thing that strikes me in your question is you want the data being displayed in your app to be up to date with what is on the server. On a high level, a really good way to do this is to use iOS's ability to multitask and perform functions for you when you app is in the background. You would need to register with the OS as an app that performs fetches to a server in the background.
According to Apple's documentation, "In Xcode 5 and later, you declare the background modes your app supports from the Capabilities tab of your project settings. Enabling the Background Modes option adds the UIBackgroundModes key to your app’s Info.plist file." From there you would need to research the UIApplicationDelegate's protocol methods – application:performFetchWithCompletionHandler: and -application:handleEventsForBackgroundURLSession:completionHandler:.
Also, you will need to look into NSURLSession a little more. If you want to use background fetching, NSURLSessionDataTask is not supported. You will need to use NSURLSessionDownloadTask, save the response to a file and process it however you need to. Also, as the app delegate method name above implies, you will need to read the NSURLSessionConfiguration Class Reference, specifically about backgroundSessionConfiguration.
The really cool thing about all of this is, after you have implemented it, your app UI will be up to date for the user – even if your app was killed by the user or by the OS. Pretty nifty.
Good luck and hope this all helps. I hope I didn't miss any other big pieces here.
I think it a personal preference. So I personally do it on the model objects. Lets say I have a Car object and a ShowroomViewController. I always declare a class method to Car object to call service to get all the cars.
#interaface Car
+(void)fetchCarsWithCompletionHandler:(void (^)(NSArray* cars, NSError *error ))handler;
-(void)getDetailsWithCompletionHandler:(void (^)(Car* car, NSError *error ))handler;
#end
Then call the class method on viewWillAppear(If I need to update the cars very often) or viewDidload(If I need to call the service once).
The other trick I mostly do is define a flag in the view controller like
#interface ShowroomViewController
#property(assign)BOOL needsModelUpdate;
#end
and I update the modal conditionally.
#implementation ShowroomViewController
-(void)viewWillAppear:(BOOL)animated{
if(self.needsModelUpdate){
[self fetchModel]
}
}
-(void)fetchModel{
__block __weak ShowroomViewController *weakRef=self;
[Car fetchCarsWithCompletionHandler:^(NSArray *cars, NSError *error) {
[weakRef setCars:cars];
[weakRef.tableView reloadData];
}];
}
#end
The reason I define this flag is I can change it somewhere else lets say applicationDidEnterBackground: method the change the flag. Or you can use KVO but I always find it overkill .
Do it however you want.
Personally, I create a class specifically for all communication with the server. Actually, my App has around 20 classes for different parts of the communication process. But yours is probably less complicated.
Add an instance of the class as an object in an xib file or else create an instance of it inside the app delegate's init method.
Use didEnterForeground to tell the other class that it needs to do it's stuff, but still use the init method to create an instance of the class.
I am new to ios app development.could you please tell me how to download two or more images asynchronously using NSURLconnection. I can do it for one one image but seeks some help to do it for two or more images.
To do this I usually have a helper class which downloads an image given a URL that calls me back when it's done. I've actually released that code as part of my MJGFoundation project. Take a look at the class called MJGImageLoader.
Essentially it's very straight forward and what I do is wrap all the NSURLConnection handling into a single class which you then start by passing a block which will be run on completion. I suggest you either take my code there and use it or look at how I've done it and replicate it yourself according to your needs.
create a separate class lets say - ConnectionManager having NSURLconnection complete implementation. create a protocol in the same class.
in the controller, make object of ConnectionManager pass delegate as self and start downloading one file. on completion, ConnectionManager can trigger your delegate and can deliver you the downloaded data.
to download multiple files simultaneously, you need to make multiple objects of ConnectionManager and start your requests. With that you will also require to handle the delegate as to recognize, which request is triggering your delegate.
hope it'll help somewhat.