What is the difference between handler and asynctask in android

AsyncTask contains three generic parameters: Params, the parameter type required for asynchronous task execution; Progress, the type of asynchronous task execution progress; Result, the type of asynchronous task execution result. It is not necessary to use all three parameters. The unused parameters can be set to Void, for example:. The four important methods of AsyncTask: When an asynchronous task is executed, there are four steps: onPreExecute , executed in the UI thread, it will be executed before the start of the asynchronous task, generally used to set the task parameters; doInBackground , the most important The method is executed in the child thread in fact, only it is executed in the child thread, the other methods are executed in the UI thread.

When onPreExecute ends, this method is executed immediately. It is used to perform time-consuming calculations in the background. The parameters of the asynchronous task will be passed to it, and the result of the execution will be sent to the fourth step; during the execution, it can also call publishProgress Methods to notify the UI thread of the current execution progress; onProgressUpdate , when publishProgress is called, it is executed in the UI thread, refresh the task progress, generally used to refresh the progress bar and other UI components; onPostExecute , when the background asynchronous task is completed, it Will be called in the UI thread and get the result of the asynchronous task execution completion.

Through the above analysis, we can see that the relationship between Handler and AsyncTask is not too big, it can be said that it is not something on the same level. However, they have some common purpose, that is, they can all be used to execute some code asynchronously to avoid blocking the UI thread.

In addition, AsyncTask is actually implemented using Handler and thread pool technology. Tech Community Register Log in. The difference between Handler and AsyncTask in Android. FaceBook Share. The origin of the problem Recently, I always saw someone asking the difference between Thread and AsyncTask in Android, so I studied it and summarized it as follows. So, when the Handler communicates, it just gives a message to the caller thread and it will wait to process. If you use Java threads then you need to handle the following requirements in your own code: Synchronization with the main thread if you post back results to the user interface No default for canceling the thread No default thread pooling No default for handling configuration changes in Android AsyncTask AsyncTask enables proper and easy use of the UI thread.

An asynchronous task is defined by a computation that runs on a background thread and whose result is published on the UI thread. Invoked on the background thread immediately after onPreExecute finishes executing. Invoked on the UI thread after a call to publishProgress Progress Why should you use AsyncTask? Easy to use for a UI Thread. So, use it when the caller thread is a UI thread. No need to manipulate Handlers. URL urldisplay.

So you can do UI changes in the same class implementation without using Handler and message passing. Of course, you can communicate between two threads in other ways, but there are many disadvantages and dangers due to thread safety issues. That is why you should use Handler and AsyncTask. They do most of the work for you, you just need to know what methods to override. This site uses Akismet to reduce spam. Learn how your comment data is processed. And a Thread is basically the core element of multithreading which a developer can use with the following disadvantage: If you use Java threads you have to handle the following requirements in your own code: Synchronization with the main thread if you post back results to the user interface No default for canceling the thread No default thread pooling No default for handling configuration changes in Android And regarding the AsyncTask , as the Android Developer's Reference puts it: AsyncTask enables proper and easy use of the UI thread.

Daniel F Daniel F In that lecture series, this link will take you right into some thread examples: youtu. After looking in-depth, it's straight forward. AsyncTask : It's a simple way to use a thread without knowing anything about the java thread model.

Use for small waiting operations like the following: Fetching some data from web services and display over the layout. Database query. When you realize that running operation will never, ever be nested. It's the best fit for: It allows you to do message queuing. Message scheduling.

Thread : Now it's time to talk about the thread. Lavekush Agrawal Lavekush Agrawal 5, 6 6 gold badges 47 47 silver badges 84 84 bronze badges. AsyncTask api is, in fact, written with Futures, Handlers, and Executors. See source code: grepcode. Eugene S Eugene S 3, 17 17 silver badges 34 34 bronze badges.

Thread Android supports standard Java Threads. AsyncTask If you have an Activity which needs to download content or perform operations that can be done in the background AsyncTask allows you to maintain a responsive user interface and publish progress for those operations to the user.

For more information you can have a look at these links. Ravindra babu Harshal Benake Harshal Benake 2, 1 1 gold badge 22 22 silver badges 41 41 bronze badges. Handler : A Handler allows you to send and process Message and Runnable objects associated with a thread's MessageQueue.

There are two main uses for a Handler : To schedule messages and runnables to be executed as some point in the future; To enqueue an action to be performed on a different thread than your own. Drawbacks: By default, an app pushes all of the AsyncTask objects it creates into a single thread. HandlerThread : You may need a more traditional approach to executing a block of work on a long-running thread unlike AsyncTask, which should be used for 5ms workload , and some ability to manage that workflow manually.

ThreadPoolExecutor : This class manages the creation of a group of threads, sets their priorities, and manages how work is distributed among those threads. If the workload is more and single HandlerThread is not suffice, you can go for ThreadPoolExecutor However I would like to have a socket connection run in service. If you want to communicate back to UI thread, you can use one more Handler to process response. Ravindra babu Ravindra babu Brian Brian 7, 15 15 gold badges 62 62 silver badges bronze badges.

Or is it more recommended to make use of it? AeroDroid In your example: "a simple while true ", you will peg the CPU here unless you add a sleep state in the loop.

This is true of any endless loop. If you want to reduce CPU usage due to this overhead, sleep the thread for a few milliseconds at the end of the loop. Error - that is interesting! If you had to pick an appropriate number for the sleep time, would it be between milliseconds? Actually developer. You should also use them carefully since they can be dismissed by the system without executing!

Show 4 more comments. Rohit Poudel 1, 2 2 gold badges 18 18 silver badges 20 20 bronze badges. It depends which one to chose is based on the requirement Handler is mostly used to switch from other thread to main thread, Handler is attached to a looper on which it post its runnable task in queue.

All Async Tasks share the same background thread for execution which also impact the app performance Thread is used in app for background work also but it doesn't have any call back on main thread. In the FlickrAdapter, the choices I could think of: Choice 1: Create a LooperThread [extends thread] - and keep on downloading images sequentially in one thread by keeping this thread open [looper.

Choice 4: Make use of AsyncTask to download the images in background, but here I will not have access to the number of threads I want in the thread pool and it varies with different android version, but in Choice 3 I can make of conscious decision of the size of thread pool depending on device configuration being used.

Alexander Farber May I know the reason why my explanation on the basis of an example for analogy sake has been down-voted, so that I also learn from it? My initial question is not answered at all, you're giving an example and explain how it works, but the questions asks for differences between handler, asynctask and thread.

Thread When you start an app, a process is created to execute the code. To prevent this, you can create worker threads and run background or long running tasks. Handler Since android uses single thread model, UI components are created non-thread safe meaning only the thread it created should access them that means UI component should be updated on main thread only.

AsyncTask AsyncTask provided by android uses both thread and handler to make running simple tasks in the background and updating results from background thread to main thread easy. Arnav Rao Arnav Rao 5, 1 1 gold badge 29 29 silver badges 30 30 bronze badges. In android it is mostly used to communicate with main thread by creating and sending messages through handler AsyncTask - is used to perform long running applications in a background thread.

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