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    <h2>Why to use Handler in Android?</h2> <hr> <p><strong>First: Let us know what is thread:</strong></p> <ul> <li>Threads help in multi-tasking</li> <li>Threads can be taught as a mini process running under a main process</li> <li>Threads enable at-least the appearance parallel execution</li> </ul> <p><strong>Second: Let us know about the application thread:-</strong></p> <ul> <li>When the android application is first started the runtime system will create a single main thread, this main thread will take care of execution of all the components in android</li> </ul> <hr> <p><strong>Android UI-Toolkit is not thread safe</strong></p> <ul> <li><em>As stated there are many components in the android main thread, now suppose one of the components takes a long time for execution then this makes the main thread <strong>unresponsive</strong> and it will <strong>show the application unresponsive</em></strong></li> <li>Sub-threads cannot directly manipulate the application (main) thread in the android </li> <li>Handler acts as a interface and collects the messages from the sub-threads and update the main application thread one by one as the messages arrive, Thread handlers are implemented in main thread.</li> </ul> <hr> <p><strong>Handler class:</strong></p> <ul> <li>For the purpose of multithreading we shall use handler class which comes from the package <code>android.os.Handler</code></li> <li>Each thread is handled by one instance of handler class</li> </ul> <p><img src="https://i.stack.imgur.com/7ZPwd.png" alt="Figure"></p> <ul> <li>From the above figure we can see that Each thread is handled by one instance of the Handler class</li> <li>threads communicate between each other with the help of messages</li> <li>This handler class helps to maintain kind of sync-coordination b/w threads by allowing them to run together achieving multithreading</li> </ul> <hr> <p><strong>Instance of handler is made</strong> </p> <pre><code>Handler handlerObject = new Handler(); </code></pre> <hr> <p><strong>Final piece on using handler is to use Runnable Interface:</strong></p> <ul> <li>handler class utilizes runnable interface to implement multithreading</li> <li>We override run method to execute a thread a specified number of time</li> </ul> <hr> <pre><code>Class NameOfClass implements Runnable { Public void run() { //Body of run method } } </code></pre> <hr> <p><strong>Putting all together</strong></p> <pre><code>//Create handler in the thread it should be associated with //in this case the UI thread final Handler handler = new Handler(); Runnable runnable = new Runnable() { public void run() { while(running){ //Do time consuming stuff //The handler schedules the new runnable on the UI thread handler.post(new Runnable() { //Ex.. using progressbar to set the pogress //Updating the UI is done inside the Handler }); } } }; new Thread(runnable).start(); </code></pre>
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    1. POWhy use Handler?
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    1. USMartijn Pieters
    1. USDevrath
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    1. COWhy there are two "Run() methods in new Runnable() body? Could it be done only with one method?
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      1. USMarek
    2. CO@ Marek ..... I have updated the answer & made the example much simpler :)
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    3. COWhat about that simple solution: runOnUiThread(new Runnable() { public void run() { } });
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