You must remember to call task resume to actually start the task, as all session tasks begin in the suspended state. An nsurlsessiondownloadtask downloads the file to a temporary location on the ios device. How to use nsurlsession to download and save a file. Check out the sample app code at the end of the tutorial to see how to save the image to your photo album. Canceling a download task, however, stops the task and it isnt possible to resume it at a later time. Urlsessiondownloadtask not working apple developer forums. Stream tasks establish a tcpip connection from a host name and port or a net service object. One example of this integration is nsurlsession s outofprocess. Posts about nsurlsessiondownloadtask written by aswath hasina. Nsurlsession cannot be created in the background unless the. I created a simple download task to test a video file like. Sep 23, 2016 if youve started migrating to swift 3. There are also several delegates available in the nsurlsession api.
It is possible to suspend a download task and resume it at a later time. But as above, checking in the cache folder, i can see the download going but when it completes, it never gets moved out of the cache folder and the handle delegate doesnt get called. In the completionhandler, you can save this file permanently. Delegate method is in nsurlsessiontaskdelegate sent periodically to notify the delegate of upload progress. Creates a download task to resume a previously canceled or failed download and calls a handler upon completion. Rather than being allocinitd directly, tasks are created by an nsurlsession. Unlike nsurlsessionuploadtask and nsurlsessiondownloadtask we cannot pause and resume the downloadupload.
I sorta feel like i might be able to do this with continuewith and some polling of the download task info but i havent yet figured out how to do that. Jun 16, 2016 utilizing the ios background with xamarin. Further than that, the newly created download task is assigned to the downloadtask of the fdi object, so we can have a strong reference to it and access it directly later on. This is quite different from a regular data task that stores the response in memory. I am trying to figure out how to use nsprogress with a nsurlsession download task. The python server sample here doesnt support streaming data transfer. The app downloads a bunch of feeds, and passes data to a streaming xml parser, one per download, as it arrives. Jun 12, 2019 if found, youll create a new download task by invoking downloadtaskwithresumedata.
Finally, we have the nsurlsession download task which is basically our request. Create a destination url create url to the source file you want to download use urlsession. If tasks complete while the application is backgrounded, suspended, or terminated, ios will notify the application by calling the completion handler in. Ive got plans to update a bunch of posts but lets start with the simplest stuff. And ios and tvos and watchos i havent found an easy way to get summary details or statistics from the session manager, but since it works on a queue to upload or download things, my guess is you have one or more jobs timing out. It is possible to cancel a download task and resume it at a later point. In this post i will build on top of the previous simple code and show how to implement a custom delegate for nsurlsession tasks in previous sample, i used self to implement all delegate methods. Whether your app is in the foreground, suspended, or sitting in the background, it can download as much data as it wants without the time. If found, youll create a new download task by invoking downloadtaskwithresumedata. Defaultsessionconfiguration, new mysessiondelegatethis as insurlsessiondelegate, nsoperationqueue.
I create simple shellscript file to stop nsurlsession processes. One nsurlsession can have multiple task object to do different tasks. It could be an image file, video file or even a zip archive or a large size. If the app frequently updates its content from remote sources or if it occasionally performs large data transfers like downloading audio or video files, since ios 7 its possible to run this kind of tasks while the app is in the background. Nsurlsessiondownloadtask foundation apple developer.
Listing 1 shows a simple example of creating a download task with a completion. Aug 24, 2016 since nsurlconnection is deprecated, ios developers are in a point to move to nsurlsession. The number of bytes that this task has sent in the request body. The first thing you need to know is that its not called nsurlsession anymore. Most of the methods associated with this class are documented in nsurlsession task download tasks directly write the servers response data to a temporary file, providing your app with progress updates as data arrives from the server. Lets start this new tutorial by creating a new swift ios single view application for this tutorial well use ios 9 as a deployment target and the examples are based on a server side script to get the data located on the server that does not have the s, so, for this reason, we have to edit the info. To create our inprocess session we simply do the following. This is because the task complete nsurlsession delegate methods are called at the session objects delegate.
The nsurlsession stream task class provides an interface a tcpip connection created via nsurlsession. If i was you i would search for an example of how to download multiple files using nsurlsession to get the pattern right. If tasks complete while the application is backgrounded, suspended, or terminated, ios will notify the application by calling the completion handler in the applications appdelegate. This site uses cookies for analytics, personalized content and ads. I talked about the advantages it has over nsurlconnection and how to use nsurlsession for simple tasks, such as fetching data from a web service and downloading an image from the web. Check out the sample app code at the end of the tutorial to see how to save the image to your.
In this tutorial we will create a simple single view application. I have tried wiring in the urlsession delegate but i dont seem to get any callbacks. The principal difference with upload and download tasks is that they. Downloadfileasync, but i have read that it is recomended to use nsurlsession for ios. That daemon is invoked and services download need for called from many apps and many services on macos. Mar 04, 2014 now that weve been introduced to all the objects that make up nsurlsession api, lets move on to writing code to download an image with nsurlsession. The code isnt pretty, the organization of code is flawed, but it highlights all the important parts. Unfortunately, not everything can be abstracted, including running code in the background. This information is also available as properties of the task. In this post we will deeply travel through nsurlsession api. Part 2 the background transfer service in ios is a service that allows your app to download or upload large amounts of data in the background with no time limits. I do want the file to continue downloading in the background if possible, but it isnt required. Dec 22, 2014 before we take a closer look at resuming a download task, it is important to understand the difference between canceling and suspending a download task.
Nsurlsessiondownloadtask class foundation microsoft docs. Download tasks are supported in any type of session. Nov 07, 2014 learn nsurlsession using swift part 3 upload. Our podcast client is already able to show a list of episodes, but it currently lacks the ability to download individual episodes. For creating network requests i see most of the lazy people go for 3rd party frameworks or libraries. January 17, 2015 background fetching using nsurlsession. A background transfer is initiated by configuring a background nsurlsession and enqueuing upload or download tasks. The upload and download tasks are the only types of tasks that can be run outofprocess, and the download task is the only task that can be paused and then resumed later.
The most significant difference with data tasks is that a download task writes its response directly to a temporary file. Making networking calls using nsurlsession and parsing the resulting json. The number of bytes this task expects to send in the request body. Showing the file download progress with nsurlsessiondatatask. How to cancel a nsurlsessiondownloadtask xamarin community. When a download task is canceled, it has the option to create resume data, which can then be passed when creating a new download task to pick up where it left off. How to download files with urlsession and downloadtask free. Most mobile apps arent open very often and tend to stay in the foreground for short time. Nsurlsession is replacement for nsurlconnection and this api gives your app the ability to perform background downloads when your app is in background left images explains how nsurlconnection works, and right image explains how nsurlsession works. Invalid resume data for background download, b ackground downloads must use or s and must download to an acessable file excude the spelling, this editor complains of invalid characters im guessing when resuming the download task withresumedata, uses the incorrect path for initing the existing downloaded data. As mentioned in the previous tutorial, nsurlsessiondatatask is typically used to perform get requests where data returned from the server is accessible in memory as an nsdata object.
Learn nsurlsession using swift part 3 upload swift. Now, im going to pause and eventually get around to going through the rest of this code, but i want to talk about this nsurlsession download task more. Analysis of sampling nsurlsessiond pid 392 every 1 millisecond. When your app no longer needs a session, invalidate it by calling either either invalidateandcancel to cancel outstanding tasks or finishtasksandinvalidate to allow outstanding tasks to finish before invalidating the object. Use nsurlsession to implement download task break point. As you can imagine, asynchronicity is a key concept in nsurlsession. Youll start by creating a data task to query the itunes search api for the users search term. Jan 17, 2015 january 17, 2015 background fetching using nsurlsession. Forms team has spent a lot of time abstracting the major mobile platforms for developers, so that we can focus on building great apps. In a previous tutorial i presented a specific new multitasking feature in ios 7, the background fetch, showing how easy it is to make an app to schedule downloads in the background. Im creating an app that needs to download and save a large file over 600mb. An nsurlsession download task is a concrete subclass of nsurlsession task. In this tutorial, i am going to work with another great multitasking feature, named background transfer service prior to ios 7, only a few kinds of application were allowed to download resources or.
Download tasks download a resource directly to a file on disk. The number of bytes this task has received in the response body. With this short code example i am going to share with you how to download a large file from a remote url. Steps to reproduce implement a nsurlsessiondownloaddelegate to handle downloading. Nsurlsession cannot be created in the background unless. A nsurlsession data task is a concrete subclass of nsurlsession task. Because the standard caching system is not used and we dont need a special authentication policy to be able to download the files from the web server, were using the default configuration for the nsurlsession object created by the method nsurlsession sharedsession. But in real life application, you are going to need. We create a download task using the nsurlsession class method and configure its request, and provide a description for use later. How do you know which feed is associated with which task.
Opposite to the download task, this task is mainly used for sending files to the server. During upload of the body data if your app provides any, the session periodically calls its delegates urlsession. Nsurlsession class is introduced in ios 7 and os x v10. When a new download task gets started, this property gets the taskss identifier value, so it stops having the. I have tried to cancel an active task, but it never seems to stop until it is done. Use nsurlsession to implement download task break point continue example. Im using the new nsurlsession api and allowing the user to download files. The download task is actually a subclass of this base class, called the nsurlsessiontask. By continuing to browse this site, you agree to this use.
The body of the request will be created from the file referenced by fileurl nsurlsessionuploadtask uploadtaskwithrequest. How to use nsurlsession to download and save a file unity forum. When a task completes, the nsurlsession object calls the task s completion handler. My understanding is that the task can finish in background, reopen the app, and resume. If the resume data is absent for any reason, youll create a new download task with the download url. Downloading files from websites apple developer documentation. If each nsurlsession datatask had its own delegate, you could give that delegate a feed property. Nov 02, 2015 finally, we have the nsurlsession download task which is basically our request. Nsurlsession download task a url session task that stores downloaded data to file.
This is an infuriating design feature of nsurlsession but apple did it to simplify background sessions, which isnt relevant here. Wkurlsessionrefreshbackgroundtask apple developer forums. Not able to find where is the issue, above people suggested to diagnostic the problem, i did and here s the cause of crash and update progress also chensmile may 4 16 at 8. Nsurlsession is replacement for nsurlconnection and this api gives your app the ability to perform background downloads when your app is in background left images explains how nsurlconnection. If the app frequently updates its content from remote sources or if it occasionally performs large data transfers like downloading audio or video files, since ios 7 its possible to run this kind of tasks while the. Downloading files in background with urlsessiondownloadtask. Use the createdownloadtask method on the nsurlsession to create a download task from an nsmutableurlrequest. The following sample code shows how to download an object body with the background transfer service. Now that weve been introduced to all the objects that make up nsurlsession api, lets move on to writing code to download an image with nsurlsession. Nsurlsession use tasks to implement network request, file download or file upload.
One example of this integration is create a download task. Id like to try to avoid managing the download tasks myself, would be much better if i could tell the system how many to allow instead that would be better. Nsurlsessionuploadtask is not having any special delegate class. Nsurlsession also makes it incredibly easy to download images.
The methods in the nsurlsession data task class are documented in nsurlsession task a data task returns data directly to the app in memory as one or more nsdata objects. Id like to try and tell my nsurlsession how many simultaneous downloads to run, but i dont see a way to do it. In this tutorial, well take a closer look at the configuration options of nsurlsession and how to cancel and resume a download task. Tasks may be created from an nsurlsession using the stream task with host name.
In the previous tutorial, i introduced you to nsurlsession. Nov 29, 20 iphone application development networking fetching data over network is yet another important concept to become familiar with in the process of learning ios application development. Create your own nsurlsession instance, and set its delegate property. In this fourth and final tutorial about nsurlsession, well take a closer look at outofprocess tasks, download tasks in particular. Urlsessiontest is a minimal test app to show how to use nsurlsession to upload files in the background. Nsurlsessiontask foundation apple developer documentation. Since nsurlconnection is deprecated, ios developers are in a point to move to nsurlsession. I start an upload task, i kill the app by swiping it off.
814 325 1151 926 464 1184 763 192 1592 1607 507 315 1107 1270 181 320 1059 500 1010 1364 1645 754 877 808 1134 923 568 951 431 449 73 582