1 page.title=Specifying the Code to Run on a Thread 2 3 trainingnavtop=true 4 @jd:body 5 6 <div id="tb-wrapper"> 7 <div id="tb"> 8 9 <!-- table of contents --> 10 <h2>This lesson teaches you to</h2> 11 <ol> 12 <li><a href="#ExtendClass">Define a Class that Implements Runnable</a></li> 13 <li><a href="#RunMethod">Implement the run() Method</a> 14 </ol> 15 16 <h2>You should also read</h2> 17 <ul> 18 <li><a href="{@docRoot}guide/components/processes-and-threads.html">Processes and Threads</a></li> 19 </ul> 20 21 22 <h2>Try it out</h2> 23 <div class="download-box"> 24 <a href="{@docRoot}shareables/training/ThreadSample.zip" class="button">Download the sample</a> 25 <p class="filename">ThreadSample.zip</p> 26 </div> <!-- download-box --> 27 28 </div> <!-- tb --> 29 </div> <!-- tb-wrapper --> 30 31 <p> 32 This lesson shows you how to implement a {@link java.lang.Runnable} class, which runs the code 33 in its {@link java.lang.Runnable#run Runnable.run()} method on a separate thread. You can also 34 pass a {@link java.lang.Runnable} to another object that can then attach it to a thread and 35 run it. One or more {@link java.lang.Runnable} objects that perform a particular operation are 36 sometimes called a <i>task</i>. 37 </p> 38 <p> 39 {@link java.lang.Thread} and {@link java.lang.Runnable} are basic classes that, on their own, 40 have only limited power. Instead, they're the basis of powerful Android classes such as 41 {@link android.os.HandlerThread}, {@link android.os.AsyncTask}, and 42 {@link android.app.IntentService}. {@link java.lang.Thread} and {@link java.lang.Runnable} are 43 also the basis of the class {@link java.util.concurrent.ThreadPoolExecutor}. This class 44 automatically manages threads and task queues, and can even run multiple threads in parallel. 45 </p> 46 <h2 id="ExtendClass">Define a Class that Implements Runnable</h2> 47 <p> 48 Implementing a class that implements {@link java.lang.Runnable} is straightforward. For example: 49 </p> 50 <pre> 51 public class PhotoDecodeRunnable implements Runnable { 52 ... 53 @Override 54 public void run() { 55 /* 56 * Code you want to run on the thread goes here 57 */ 58 ... 59 } 60 ... 61 } 62 </pre> 63 <h2 id="RunMethod">Implement the run() Method</h2> 64 <p> 65 In the class, the {@link java.lang.Runnable#run Runnable.run()} method contains the 66 code that's executed. Usually, anything is allowable in a {@link java.lang.Runnable}. Remember, 67 though, that the {@link java.lang.Runnable} won't be running on the UI thread, so it can't 68 directly modify UI objects such as {@link android.view.View} objects. To communicate with 69 the UI thread, you have to use the techniques described in the lesson 70 <a href="communicate-ui.html">Communicate with the UI Thread</a>. 71 </p> 72 <p> 73 At the beginning of the {@link java.lang.Runnable#run run()} method, set the thread to use 74 background priority by calling 75 {@link android.os.Process#setThreadPriority Process.setThreadPriority()} with 76 {@link android.os.Process#THREAD_PRIORITY_BACKGROUND}. This approach reduces 77 resource competition between the {@link java.lang.Runnable} object's thread and the UI 78 thread. 79 </p> 80 <p> 81 You should also store a reference to the {@link java.lang.Runnable} object's 82 {@link java.lang.Thread} in the {@link java.lang.Runnable} itself, by calling 83 {@link java.lang.Thread#currentThread() Thread.currentThread()}. 84 </p> 85 <p> 86 The following snippet shows how to set up the {@link java.lang.Runnable#run run()} method: 87 </p> 88 <pre> 89 class PhotoDecodeRunnable implements Runnable { 90 ... 91 /* 92 * Defines the code to run for this task. 93 */ 94 @Override 95 public void run() { 96 // Moves the current Thread into the background 97 android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_BACKGROUND); 98 ... 99 /* 100 * Stores the current Thread in the PhotoTask instance, 101 * so that the instance 102 * can interrupt the Thread. 103 */ 104 mPhotoTask.setImageDecodeThread(Thread.currentThread()); 105 ... 106 } 107 ... 108 } 109 </pre> 110
