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> 27 </div> 28 29 </div> 30 </div> 31 32 <p> 33 This lesson shows you how to implement a {@link java.lang.Runnable} class, which runs the code 34 in its {@link java.lang.Runnable#run Runnable.run()} method on a separate thread. You can also 35 pass a {@link java.lang.Runnable} to another object that can then attach it to a thread and 36 run it. One or more {@link java.lang.Runnable} objects that perform a particular operation are 37 sometimes called a <i>task</i>. 38 </p> 39 <p> 40 {@link java.lang.Thread} and {@link java.lang.Runnable} are basic classes that, on their own, 41 have only limited power. Instead, they're the basis of powerful Android classes such as 42 {@link android.os.HandlerThread}, {@link android.os.AsyncTask}, and 43 {@link android.app.IntentService}. {@link java.lang.Thread} and {@link java.lang.Runnable} are 44 also the basis of the class {@link java.util.concurrent.ThreadPoolExecutor}. This class 45 automatically manages threads and task queues, and can even run multiple threads in parallel. 46 </p> 47 <h2 id="ExtendClass">Define a Class that Implements Runnable</h2> 48 <p> 49 Implementing a class that implements {@link java.lang.Runnable} is straightforward. For example: 50 </p> 51 <pre> 52 public class PhotoDecodeRunnable implements Runnable { 53 ... 54 @Override 55 public void run() { 56 /* 57 * Code you want to run on the thread goes here 58 */ 59 ... 60 } 61 ... 62 } 63 </pre> 64 <h2 id="RunMethod">Implement the run() Method</h2> 65 <p> 66 In the class, the {@link java.lang.Runnable#run Runnable.run()} method contains the 67 code that's executed. Usually, anything is allowable in a {@link java.lang.Runnable}. Remember, 68 though, that the {@link java.lang.Runnable} won't be running on the UI thread, so it can't 69 directly modify UI objects such as {@link android.view.View} objects. To communicate with 70 the UI thread, you have to use the techniques described in the lesson 71 <a href="communicate-ui.html">Communicate with the UI Thread</a>. 72 </p> 73 <p> 74 At the beginning of the {@link java.lang.Runnable#run run()} method, set the thread to use 75 background priority by calling 76 {@link android.os.Process#setThreadPriority Process.setThreadPriority()} with 77 {@link android.os.Process#THREAD_PRIORITY_BACKGROUND}. This approach reduces 78 resource competition between the {@link java.lang.Runnable} object's thread and the UI 79 thread. 80 </p> 81 <p> 82 You should also store a reference to the {@link java.lang.Runnable} object's 83 {@link java.lang.Thread} in the {@link java.lang.Runnable} itself, by calling 84 {@link java.lang.Thread#currentThread() Thread.currentThread()}. 85 </p> 86 <p> 87 The following snippet shows how to set up the {@link java.lang.Runnable#run run()} method: 88 </p> 89 <pre> 90 class PhotoDecodeRunnable implements Runnable { 91 ... 92 /* 93 * Defines the code to run for this task. 94 */ 95 @Override 96 public void run() { 97 // Moves the current Thread into the background 98 android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_BACKGROUND); 99 ... 100 /* 101 * Stores the current Thread in the PhotoTask instance, 102 * so that the instance 103 * can interrupt the Thread. 104 */ 105 mPhotoTask.setImageDecodeThread(Thread.currentThread()); 106 ... 107 } 108 ... 109 } 110 </pre> 111
