battery consuming tasks when launched in the background - ios

Apple states that the app using the background mode shouldn't perform expensive, battery consuming tasks when launched in the background. What exactly is considered a batter consuming task? To be specific: is searching and array of 100 entries acceptable? What about 1000?

A battery-consuming task is just that - a task that uses so much CPU that it makes considerable "dent" on the battery, as measured by the "battery percentage" screen. To that end, searching 100, 1000, or 1000000 items a single time is unlikely to do any damage. On the other hand, searching a 10-item list fifty times a second is very likely to make your task a high energy consumer. Same goes for downloading data multiple times per minute, using location services, etc.
A rule of thumb is very simple: go to the "Last 24 hours" view of the "Battery percentage" screen, and see if your app is listed there. If it is not there, of if it is below "Home & Lock Screen", your app is fine.

The remark from the guidelines you are referencing is meant to keep people form draining a user's battery in the background.
As a lot of applications use GPS and/or radio in the background and those are way more power consuming than searching tiny arrays, searching some array will probably be fine, as long as it has a reasonable size.
You shouldn't create an app that helps SETI or Folding or searches for the next biggest prime - or excessively use radio. But for small tasks like your's, this guideline is not to be concerned. Yet, this is only an estimate and in the end, the review process will decide on this on a case by case basis.
The general rule of thumb from apple is:
Always try to avoid doing any background work unless doing so improves the overall user experience. An app might move to the background because the user launched a different app or because the user locked the device and is not using it right now. In both situations, the user is signaling that your app does not need to be doing any meaningful work right now. Continuing to run in such conditions will only drain the device’s battery and might lead the user to force quit your app altogether. So be mindful about the work you do in the background and avoid it when you can.
So the question for you to decide if this is okay is: Does the user expect that to be done right now? rather than does that use too many battery?. If searching that array cannot be deferred to when the app is active again (I cannot see a reason for not deferring it, but there might be), you are fine searching the array in background.

Related

iOS background usage of Network.Framework

I've written a simple WiFi based App using TCP on Network.Framework that receives about 80 bytes every 10s from a remote service on specific port. I want to write this data to file while in the foreground and the background.
The question is which of the background modes if any/is permitted/best fits this requirement?
All wisdom gratefully accepted.
Without knowing anything else about your app (is it a music app?, location?, VoIP?, bluetooth?) it's hard to say what you might do. But there are two classes of background actions:
Actions that are ongoing when you go to the background that can be finished.
Permitted background actions for specific kinds of apps. See "Implementing Long-Running Tasks" in the link you have about background modes.
The first doesn't really apply to you since this is ongoing. Of the second items, I'd guess that "Background fetch" is the one that fits best.
Note that you won't necessarily be called as regularly as you might like. But since your time interval is quite long (10sec) then a few hundred milliseconds latency wouldn't be particularly damaging I'd guess.
But also note that "Enabling this mode is not a guarantee that the system will give your app any time to perform background fetches. The system must balance your app’s need to fetch content with the needs of other apps and the system itself."

In iOS11, how to keep a background task running past 10 min?

My question involves keeping an app that monitors user interactions in the background, for example time spent in one or the app. The issue arises when you can not have a background process run for more than 10 min or violate Apple's sandbox restrictions. Since I am relatively new to the Apple API, and could not find a direct answer that didn't involve location services or VOIP (which are both interesting options, but my application will not be able to use either viably), I come to ask for options in which I can understand when another app opens, when it closes, when it fetches data, and when user holds phone in certain orientation (ie when people hold their phone at certain angles to read text and etc.) for certain amount of time.
The purpose of this analyzation is to predict an attention span for the user, so I need to be able to run in the background, as the user will not be using my app while it predicts attention span.
My thoughts on this are possibly accessing the system log, and somehow parse previous statements (I don't think sandbox will allow), but inevitably the iOS system will suspend my processes after some point unless I put a timer. There is also the option of having the system wake up my app via opportunistic fetching, but that won't be useful if I don't collect the data.
Keep in mind this is within IOS 11, so it is much more restrictive than previous iterations. I understand this may seem like a complex problem, but even a direction in which to head could be useful to me.
This solution might work, (not recommended since it drains the battery quicker).
Just update your current location, every 10 mins. It will reset the background thread timer.

How long an application is used in BlackBerry

I've seen is posible to know what applications are running with getVisibleApplications()from "ApplicationManager" class but, is it possible to know how long were these applications used?
Thanks
If you really needed this information it would be possible.
You could have a background process start a timer and every N minutes it could call getVisibleApplications() and keep track of what has been added or removed to the list.
The difficulty is finding the right balance between accurate data and battery life as a very small value of N (seconds/minutes) will prevent the device from sleeping and will cause severe battery life degradation. A very large value of N will have minimal effect on battery life but the data won't be very accurate.
You could also combine it with events... maybe you would monitor aggressively when the backlight was on and hourly when it's off.
Not really sure what you're trying to do so my apologies if this doesn't help at all.
Simple answer is, No you cannot the duration of how long the applications were used. Out of interest, why would you want to know that?

consistency of regionMonitoring

I am curious about why my app does not notify me sometime when I set it to be notified at same spot everyday. On iPhone 4x devices, the app uses regionMonitoring. Somedays the update is received, some days it is not.
Moreover, with significantLocationChanges also (on 3GS), the updates are not received consistently.
1) As I understand, both significantLocationChange and regionMonitoring receive updates when the device is handed off from one cell tower to the next one. Does it mean that users who live in area where the cell towers are not close by, the app will not work?
So, when there are no other parameters that can change, I am really puzzled by this behavior.
2) Does it mean that users who live in area where the cell towers are not close by, the app will not work?
3) Can I rely on regionMonitoring to notify the user consistently? What is the recommendation?
Regards. Sam.
regionMonitoring benefits from a couple other inputs to location monitoring. It triggers based on WiFi connections as well as other applications using location. Any location updates the OS receives will get run for any outstanding regions being monitored. The older significantLocationChanges is basically stuck to cell tower handoffs, and is generally less reliable in sparse cell areas.
Doesn't mean it won't work, it will just be less effective or useful.
My experience says that the regionMonitoring is the most consistent and reliable way to monitor locations without actively using GPS. It is by no means perfect, but for the majority of users, it should work with little to no issues.
I have an app that uses region monitoring and I haven't had any major complaints about accuracy at all. I made the decision to not support the 3GS and the older method for 2 reason. Few users using it, and getting smaller by the day. Secondly, it is a lot more code to support for much less accuracy and I didn't want it to detract from the overall experience, so I left it out. Hope this helps.

Handling latency while synchronizing client-side timers using Juggernaut

I need to implement a draft application for a fantasy sports website. Each users will have 1m30 to choose a player on its team and if that time has elapsed it will be selected automatically. Our planned implementation will use Juggernaut to push the turn changes to each user participating in the draft. But I'm still not sure about how to handle latency.
The main issue here is if a user got a higher latency than the others, he will receive the turn changes a little bit later and his timer won't be synchronized. Say someone receive a turn change after choosing a player himself while on his side he think he still got 2 seconds left, how can we handle that case? Is it better to try to measure each user latency and adjust the client-side timer to minimize that issue? If so, how could we implement that?
This is a tricky issue, but there are some good solutions out there. Look into what time.gov does, and how it does it; essentially, as I understand it, they use Java to perform multiple repeated requests to the server, to attempt to get an idea of the latency involved in the communication, then they generate a measure of latency that they use to skew the returned time data. You could use the same process for your application, with even more accuracy; keeping track of what the latency is and how it varies over time lets you make some statistical inferences about how reliable your latency numbers are, etc. It can be a bit complex, but it can definitely allow you to smooth out your performance. My understanding is that this is what most MMOs do as well, to manage lag.

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