Basic Grand Central Dispatch Timer
This is a fundamental tool: A simple Grand Central Dispatch timer that either fires repeatedly, or only once.
What Problem Does This Solve?
Timers are necessary for many different reasons. They could be the driving engine of a clock app, or a UI tool to refresh a display or close a screen.
This will allow “leeway,” which Apple suggests as a way to help reduce energy usage.
The timer is thread-independent. You can instantiate it on any queue that you want.
It’s incredibly simple. Just a “set and forget,” if you are firing just once, or a simple repeating callback.
It should work fine for osx, tvOS and iOS. It only depends on the Swift Foundation library.
This requires Swift Version 4.0 or above (tested with 4.2).
WHERE TO GET
You can use SPM to load the project as a dependency, by referencing its GitHub Repo URI (SSH: email@example.com:RiftValleySoftware/RVS_BasicGCDTimer.git, or HTTPS: https://github.com/RiftValleySoftware/RVS_BasicGCDTimer.git).
Once you have the dependency attached, you reference it by adding an import to the files that consume the package:
Include the Source in Your Project
This is a simple source file; not a module.
To use this, simply add the RVS_BasicGCDTimer/RVS_BasicGCDTimer.swift file to your project; copying it wherever you want.
You then instantiate the timer:
Either as a one-shot timer (in this case, 100 milliseconds), or as a repeating timer:
timeIntervalInSeconds is a double-precision floating point number, with the timer period, in seconds (not milliseconds). It is required to be a positive value over zero.
delegate is required. The timer won’t work at all without a valid delegate.
leewayInMilliseconds is the recommended “leeway” that Apple suggests that you give timers. This helps conserve energy in mobile devices.
onlyFireOnce to true in order for the timer to be a “one-shot” timer.
someContext is any data that you want returned to the callback in your delegate method. It will be available as the timer’s
queue is the GCD queue to use. Not specifying means that the default queue is used.
isWallTime asks the timer to use the “Apple Wall Clock” time. That time is absolute, and doesn’t care about whether or not the computer sleeps or has performance breaks. It tends to be more consistent.
Note that using Wall Time can lead to unexpected behavior. For example, if the app is suspended for some period of time, and is restarted, instead of continuing where it left off, the completion call may be executed immediately.
newTimer = RVS_BasicGCDTimer(timeIntervalInSeconds: 0.1, delegate: someDelegate, leewayInMilliseconds: 25.0, onlyFireOnce: true, context: someContext, queue: DispatchQueue.main, isWallTime: true)
Here, we specify a repeating timer, with no leeway, and no context data:
newTimer = RVS_BasicGCDTimer(timeIntervalInSeconds: 0.1, delegate: someDelegate, leewayInMilliseconds: 0, onlyFireOnce: false, context: nil, queue: nil, isWallTime: false)
However, there’s a lot of defaults. You can specify the exact same as such:
newTimer = RVS_BasicGCDTimer(timeIntervalInSeconds: 0.1, delegate: someDelegate)
Once the timer is instantiated, you start it by calling
You pause (suspend) a running timer by calling
If the timer is not already running, nothing happens. If it is running, then it suspends.
If repeating, the timer will repeat until it is invalidated or deinitialized:
If a “one-shot,” then the timer is invalidated as soon as it completes.
The delegate has one required method, and four optional ones (with default extension handlers). The parameter passed in is the timer object.
You can look at the timer object’s
context property for any data/functions/whatever that you want the callback to access.
This one is called at the completion of the timer. It is required:
func basicGCDTimerCallback(_ timer: RVS_BasicGCDTimer)
This one is an optional method that is called when the timer bcomes valid:
func basicGCDTimerValid(_ timer: RVS_BasicGCDTimer)
This one is an optional one that is called JUST PRIOR to a timer bcoming invalid:
func basicGCDTimerWillBecomeInvalid(_ timer: RVS_BasicGCDTimer)
This is an optional method that is called as the timer is suspended:
func basicGCDTimerSuspend(_ timer: RVS_BasicGCDTimer)
This is an optional method that is called as the timer is resumed (which includes the initial start):
func basicGCDTimerResume(_ timer: RVS_BasicGCDTimer)
There are no dependencies to use RVS_BasicGCDTimer in your project. In order to test it and run it in the module project, you should use CocoaPods to install SwiftLint, although that is not required. It’s just good practice.
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