Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available. There are some situations where you want to apply the same annotation to a declaration or type use. As of the Java SE 8 release, repeating annotations enable you to do this.
For example, you are writing code to use a timer service that enables you to run a method at a given time or on a certain schedule, similar to the UNIX cron service. Now you want to set a timer to run a method, doPeriodicCleanupon the last day of the month and on every Friday at p. To set the timer to run, create an Schedule annotation and apply it twice to the doPeriodicCleanup method. The first use specifies the last day of the month and the second specifies Friday at 11p.
The previous example applies an annotation to a method. You can repeat an annotation anywhere that you would use a standard annotation. For example, you have a class for handling unauthorized access exceptions. You annotate the class with one Alert annotation for managers and another for admins:. For compatibility reasons, repeating annotations are stored in a container annotation that is automatically generated by the Java compiler.
In order for the compiler to do this, two declarations are required in your code. The annotation type must be marked with the Repeatable meta-annotation. The following example defines a custom Schedule repeatable annotation type:. The value of the Repeatable meta-annotation, in parentheses, is the type of the container annotation that the Java compiler generates to store repeating annotations. In this example, the containing annotation type is Schedulesso repeating Schedule annotations is stored in an Schedules annotation.
Applying the same annotation to a declaration without first declaring it to be repeatable results in a compile-time error. The containing annotation type must have a value element with an array type. The component type of the array type must be the repeatable annotation type. The declaration for the Schedules containing annotation type is the following:.
There are several methods available in the Reflection API that can be used to retrieve annotations. The behavior of the methods that return a single annotation, such as AnnotatedElement.
If more than one annotation of the requested type is present, you can obtain them by first getting their container annotation. In this way, legacy code continues to work.
Other methods were introduced in Java SE 8 that scan through the container annotation to return multiple annotations at once, such as AnnotatedElement.
See the AnnotatedElement class specification for information on all of the available methods. When designing an annotation type, you must consider the cardinality of annotations of that type.
It is now possible to use an annotation zero times, once, or, if the annotation's type is marked as Repeatablemore than once. It is also possible to restrict where an annotation type can be used by using the Target meta-annotation. For example, you can create a repeatable annotation type that can only be used on methods and fields.
It is important to design your annotation type carefully to ensure that the programmer using the annotation finds it to be as flexible and powerful as possible. All rights reserved. Hide TOC. Type Annotations and Pluggable Type Systems.There is a tendency to just use Java threads or Android AsyncTasks for everything since they are well known and can do what you want.
However, not all API is equal, choosing the right method for your requirements can make your code stable, cleaner, easier to read and more intuitive. The options are sorted first by being part of the Android API or Java, then by how frequently I have encountered or used them. Perhaps the best known of the asynchronous API, AsyncTask is easy to implement and returns results on the main thread.
There are some issues with AsyncTask, for example, they are not aware of the activity or fragment lifecycle and so it is the programmer's responsibility to handle the AsyncTasks behaviour when the activity is destroyed. This means that they are not the best option for long running operations and also, if the app is in the background and the app is terminated by Android, your background processing is also terminated. This is the defacto choice for long running processing on Android, a good example would be to upload or download large files.
The upload and download may continue even if the user exits the app and you certainly do not want to block the user from being able to use the app while these tasks are going on. Loaders are a complex topic, any single implementation of Loaders probably deserved a post all for itself.
For now it would be worth pointing out that Loaders were introduced in Android Honeycomb and are part of the compatibility library. They are aware of Fragment and Activity lifecycle and can even cache loaded data.Delay and Repeat Code Execution with Handler PostDelayed - Android Studio Tutorial
I would like to bring attention to AsyncTaskLoaders as they solve a lot of problems that are inherent to AsyncTask. Android Design Patterns has an amazing write-up on Loaders and I recommend reading it to get a deeper understand of Loaders. Using JobScheduler is a little complex, luckily there is a sample of how to use JobScheduler from Google. Effectively, you have to create a Service and create a job using JobInfo.
Builder that specifies your criteria for when to run the service; such as being on a unmetered network, or when the app is charging.
It is important to remember that there is no guarantee that your code will be executed as soon as these conditions are met or the order of the execution. The general concept is similar where you have to schedule a Service to run when certain criteria are met. The Scheduled Tasks can be One-off or Periodic. No prizes for guessing what this is used for. This is very easy to use however it is context sensitive, so if you exit your Activity or Fragment, you need to clean this up by cancelling it. To be clear, there really is nothing Asynchronous about CountDownTimer.
The reason CountDownTimer is included in the list is because using this class does not block the user from using the app even when the CountDownTimer is initialised from the main thread, effectively giving a asynchronous effect.
Also keep in mind, if your update intervals are small and your processing is time consuming, you can have a back-pressure problem which will result in blocking of your execution thread. Java Threads are rather straight forward to implement. However, they are best to avoid in Android. A better option may be to use AsyncTask. Android HandlerThread, can be used to handle messages of a background thread. While the use for this is rather limited as Message handling tends to do more of a redirection rather than processing, it nonetheless provides us a way to perform some tasks on the background thread.
A possible use may be to run a Service in a background thread. FutureTask performs asynchronous processing, however, if the result is not ready yet or processing has not complete, calling get will be block the thread. Surprisingly I've used this a few time. Sometimes you want to execute a request in Google Volley in a blocking manner.
I want to repeatedly call a method after every 5-seconds and whenever I wish to to stop the repeated call of the method I may stop or restart the repeated call of the method. Here is some sample code that whats really I want to implement. Please help me in this respect I would be very thankful to you. Use a Handler in the onCreate method. Its postDelayed method causes the Runnable to be added to the message queue and to be run after the specified amount of time elapses that is 0 in given example.
Then this will queue itself after fixed rate of time milliseconds in this example.
Do it in Android's way with the help of Handler. Declare a Handler which does not leak Memory. Learn more. How to repeat a task after a fixed amount of time in android? Ask Question. Asked 6 years, 7 months ago. Active 2 years ago. Viewed 53k times. Try this stackoverflow. I think its easy to use CountDownTimer. See here for tutorial androidsolution4u. Active Oldest Votes. Junyue Cao 6 6 silver badges 12 12 bronze badges.
Gru Gru 2, 17 17 silver badges 28 28 bronze badges. For Android a Handler is preferable to a Timer: stackoverflow. Handler ; customHandler. Massimiliano Kraus 2, 4 4 gold badges 19 19 silver badges 35 35 bronze badges. Gazal Patel Gazal Patel 4 4 silver badges 9 9 bronze badges.
Suppose my scheduled time is every 10 minutes and my phone goes to Doze mode or the ideal mode or I lock the device. Will the handler still call my method after 10 minutes? Currently, it is not working. Handler only getting called when my Application Resumes. Sniper you would need to use Alarm Manager for the function to be called when the app isn't running developer. Sanket Kachhela Sanket Kachhela Hitesh Sahu Hitesh Sahu Sign up or log in Sign up using Google.
Sign up using Facebook.Its working fine and also i have one doubt can we do this in IntentService instead of Service. Now it is running in Service means in main Thread If this can be done in IntentService it will run in worker Thread, Performance counts. Can you please help me how to do in IntentService. Thank you.
I like this approach, because it works fine. I have tested for 6 hours, and it didn't stop, or slow down. Thanks. As you can see above, this code was written 5 year ago, when Android 6. Skip to content. Instantly share code, notes, and snippets.
Code Revisions 1 Stars 37 Forks Embed What would you like to do? Embed Embed this gist in your website. Share Copy sharable link for this gist. Learn more about clone URLs. Download ZIP. Example of how to create a long running timer service that survives activity destruction by moving to the foreground, and back to the background when a new activity bind to it. All Rights Reserved.
Schedule repeating alarms
I'm trying to build an Android app which will repeatedly run some process every 10 mins. As I found out Handlers are more reliable than timers or scheduling. So I'm going to develop my app using the Handlers using the given below codes. I'm little bit concerned that the below codes will create separate Handlers at each time I start the app and keep them running parallel, may be since I'm creating the Handler on onCreate.
I decided to answer my own question since I've found out how to do it right way. The Android way. First of all what I was trying to do and posted in the question is a wrong approach to my requirement. Now I'm posting this so someone else will not do it wrong way but the following way. Resource usage is higher. But not suitable to used as a scheduler. Handlers are the best way to do something repeatedly till the app is killed.
Learn more. Android Handler for repeated task - will it overlap? Asked 5 years, 6 months ago. Active 2 years, 8 months ago. Viewed 8k times. So what is the best way to keep only a single Handler runs in background at a time?
Massimiliano Kraus 2, 4 4 gold badges 19 19 silver badges 35 35 bronze badges. Just wondering: what's the context of your 'repeated work'?
Or perhaps better said: what kind of app is it? Using a Handler while your app is not in the foreground, could not the right course of action. Oct 4 '14 at Why not use a service? I don't need to miss the task by running even while in sleep mode. Can services be active while even in idle sleep mode? Or do i need to have a wake lock.
Active Oldest Votes. You can extend Application class and do your work in it. Bracadabra Bracadabra 3, 2 2 gold badges 21 21 silver badges 41 41 bronze badges.
I'll give it a try and reply u back within minutes. What Vang gave you will create only one handler, and repeat the process based on the time passed. Notice he's extending the Application class, which is only called once, that is, when your application is created when you start the application.You can see the tutorial from this web link:. This is an android app. It repeats a countdown timer again and again. This android application helps you schedule "multiple" count down timers in a linear fashion.
An app that keeps track of important events on your life's timeline.
8 ways to do asynchronous processing in Android and counting
Counts down days, sleeps, hours, minutes and seconds until Christmas. Example of a regressive timer with start and stop actions using Handler and CountDownTimer. Add a description, image, and links to the countdown-timer topic page so that developers can more easily learn about it. Curate this topic. To associate your repository with the countdown-timer topic, visit your repo's landing page and select "manage topics.
Learn more. Skip to content. Here are 26 public repositories matching this topic Language: Java Filter by language. Sort options. Star Code Issues Pull requests. Updated Jan 10, Java. A simple TODO with countdown timer.
Updated Jun 9, Java. Updated Apr 1, Java. A count down widget for verify code.Corresponding to each Timer object is a single background thread that is used to execute all of the timer's tasks, sequentially.
Timer tasks should complete quickly. If a timer task takes excessive time to complete, it "hogs" the timer's task execution thread. This can, in turn, delay the execution of subsequent tasks, which may "bunch up" and execute in rapid succession when and if the offending task finally completes.
After the last live reference to a Timer object goes away and all outstanding tasks have completed execution, the timer's task execution thread terminates gracefully and becomes subject to garbage collection. However, this can take arbitrarily long to occur. By default, the task execution thread does not run as a daemon threadso it is capable of keeping an application from terminating.
If a caller wants to terminate a timer's task execution thread rapidly, the caller should invoke the timer's cancel method. If the timer's task execution thread terminates unexpectedly, for example, because its stop method is invoked, any further attempt to schedule a task on the timer will result in an IllegalStateExceptionas if the timer's cancel method had been invoked.
This class is thread-safe: multiple threads can share a single Timer object without the need for external synchronization. This class does not offer real-time guarantees: it schedules tasks using the Object. Java 5. Implementation note: This class scales to large numbers of concurrently scheduled tasks thousands should present no problem. Internally, it uses a binary heap to represent its task queue, so the cost to schedule a task is O log nwhere n is the number of concurrently scheduled tasks.
Implementation note: All constructors start a timer thread. Since: 1.
Android Notes 48: How to repeat a function (Timer)
The associated thread does not run as a daemon. A daemon thread is called for if the timer will be used to schedule repeating "maintenance activities", which must be performed as long as the application is running, but should not prolong the lifetime of the application.
Parameters: isDaemon - true if the associated thread should run as a daemon. Parameters: name - the name of the associated thread Throws: NullPointerException - if name is null Since: 1.