It is a very important concept in iOSdevelopment RunLoop. It provides an event loop mechanism for handling various events, such as user interaction, network requests, timers, etc. RunLoopNot only is it iOSone of the core in development, but it is also widely used in the development of other platforms. This article will introduce you to Swiftthe RunLoopbasic concepts and usage methods.

What is RunLoop?

RunLoopIt is an event loop mechanism that is used to iOShandle various events in applications. RunLoopRunning in the main thread of the application, it is responsible for managing events in that thread and ensuring that important tasks such as UI updates can be performed smoothly. RunLoopAlso responsible for handling events sent by other threads, such as network requests and so on.

RunLoopThe basic idea is to process events in a loop. When RunLoopstarted, it enters an infinite loop waiting for an event to occur. When an event occurs, RunLoopthe corresponding processing method will be called to handle the event and continue to wait for the next event to occur. RunLoopWill continue to run until manually stopped or the application exits.

RunLoop and threads

In iOS, each thread has one RunLoop, but by default, RunLoopit is disabled. To use it RunLoop, you must start it manually and add it to the thread’s run loop.

For example, to use it in the main thread RunLoop, you can use the following code:

RunLoop.current.run()

This will start the main thread RunLoopand enter an infinite loop waiting for events to occur.

RunLoop mode

RunLoopPattern is RunLoopan important concept that defines RunLoopthe types of events that need to be handled during operation. A RunLoop can have multiple modes, but only one mode can be processed at any time. Each mode can contain multiple input sources （input source）and timers （timer）, and RunLoopthe processing method of the next event will be determined based on the input sources and timers in the current mode.

RunLoopSeveral built-in modes are provided, such as:

1. NSDefaultRunLoopMode:Default mode, handles all UIevents, timers and PerformSelectormethods.
2. UITrackingRunLoopMode: Tracking mode, only handles events related to interface tracking, such as UIScrollViewscroll events.
3. NSRunLoopCommonModes: Public mode, including both NSDefaultRunLoopModeand UITrackingRunLoopMode. RunLoopIt also allows developers to customize the mode to meet specific needs.

timer

In iOSdevelopment, timer is a common event, such as refreshing at regular intervals UI, performing background tasks, etc. RunLoopA timer mechanism is provided （timer）to perform an operation within a specified time interval.

For example, to create a timer and start it in the main thread, you can use the following code:

let timer = Timer(timeInterval: 1.0, repeats: true) { timer in //  } RunLoop.current.add(timer, forMode: .common)

This will create a timer that fires every 1 second and add it to the main thread in public mode RunLoop.

When adding a timer, you need to specify RunLoopthe mode it belongs to. If mode is not specified, it defaults to NSDefaultRunLoopMode. You can use this if you need to respond to timer events in multiple modes NSRunLoopCommonModes.

input source

An input source （input source）is a RunLoopmechanism used with javascript to handle asynchronous events such as network requests, file reads and writes, and so on. RunLoopDuring the running process, it will check whether there is an input source that needs to be processed in the current mode, and if so, it will be processed immediately.

The input source can be one Port、Socket、CFFileDescriptorand so on. To use an input source, you must add it to RunLoopand set a callback function to handle input events.

For example, to use the input source in the main thread, you can use the following code:

let inputSource = InputSource()
inputSource.setEventHandler {
    // 
}
RunLoop.current.add(inputSource, forMode: .common)

This will create an input source and add it to the main thread in public mode RunLoop.

Perform Selector

Perform SelectorIt is a way to call a method in RunLoopwhich a method can be executed asynchronously. When calling a method, you can set the delay execution time and RunLoopmode. This method will be executed at the specified time interval until canceled.

For example, to use it in the main thread Perform Selector, you can use the following code:

RunLoop.current.perform(#selector(doSomething), target: self, argument: nil, order: 0, modes: [.default])

This will execute the method asynchronously in default mode doSomething.

Common operations of RunLoop

In addition to the above basic operations, RunLoopother commonly used operations are also provided, such as:

1. stop: Stopped RunLoopoperation.
2. runUntilDate: Run RunLoopuntil the specified date.
3. runMode: Run RunLoopthe event processing loop in the specified mode.
4. currentMode: Get RunLoopthe current running mode.

RunLoop and thread safety

In iOSdevelopment, multi-threading is a common problem. RunLoopWhen handling asynchronous events, thread unsafe issues may occur. To ensure RunLoopthread safety, you can use the following methods:

1. Used RunLoopQueuein a queue RunLoopto perform asynchronous operations.
2. Use it in the main thread RunLoopto handle asynchronous events to avoid cross-thread operations.

in conclusion

RunLoopIt is iOSa very important concept in development. It provides an event loop mechanism for handling various events. RunLoopThe basic idea is to process events in a loop. When an event occurs, RunLoopthe corresponding processing function will be called to handle the event. RunLoopIt also provides timers, input sources, and Perform Selectorother mechanisms to handle asynchronous events. Understanding RunLoopthe working principle can help us better understand iOSthe operating mechanism of the application and avoid some strange problems.

Finally, let’s take a look at RunLoopsome things to note:

1. Don’t block in the main thread RunLoop, otherwise it will cause UIlag.
2. Avoid using RunLoopthis NSDefaultRunLoopModemode because a large number UIof events will be processed in this mode, which may cause other events to not be processed in time.
3. During use RunLoop, you need to pay attention to thread safety issues.

RunLoopIt is an event loop mechanism through which we can easily handle various events and avoid some strange problems. In daily development, we need to use it frequently RunLoop, so it is recommended that you practice more and master RunLoopvarious usages.