Android应用程序线程消息循环模型分析（4）

接下来我们再看看应用程序的配置文件AndroidManifest.xml：

                               <?xmlversion="1.0"encoding="utf-8"?>     
                       <manifestxmlns:android="http://schemas.android.com/apk/res/android"     
                       package="shy.luo.counter"     
                       android:versionCode="1"     
                       android:versionName="1.0">     
                       <applicationandroid:icon="@drawable/icon"android:label="@string/app_name">     
                       <activityandroid:name=".Counter"     
                       android:label="@string/app_name">     
                       <intent-filter>     
                       <actionandroid:name="android.intent.action.MAIN"/>     
                       <categoryandroid:name="android.intent.category.LAUNCHER"/>     
                       </intent-filter>     
                       </activity>     
                       </application>     
                       </manifest>

这个配置文件很简单，我们就不介绍了。再来看应用程序的界面文件，它定义在res/layout/main.xml文件中：

                            <?xmlversion="1.0"encoding="utf-8"?>
                <LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"
                android:orientation="vertical"
                android:layout_width="fill_parent"
                android:layout_height="fill_parent"
                android:gravity="center">
                <LinearLayout
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:layout_marginBottom="10px"
                android:orientation="horizontal"
                android:gravity="center">
                <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginRight="4px"
                android:gravity="center"
                android:text="@string/counter">
                </TextView>
                <TextView
                android:id="@+id/textview_counter"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:gravity="center"
                android:text="0">
                </TextView>
                </LinearLayout>
                <LinearLayout
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:orientation="horizontal"
                android:gravity="center">
                <Button
                android:id="@+id/button_start"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:gravity="center"
                android:text="@string/start">
                </Button>
                <Button
                android:id="@+id/button_stop"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:gravity="center"
                android:text="@string/stop">
                </Button>
                </LinearLayout>
                </LinearLayout>

这个界面配置文件也很简单，等一下我们在模拟器把这个应用程序启动起来后，就可以看到它的截图了。应用程序用到的字符串资源文件位于res/values/strings.xml文件中：

                    <?xmlversion="1.0"encoding="utf-8"?>
            <resources>
            <stringname="app_name">Counter</string>
            <stringname="counter">Counter:</string>
            <stringname="start">StartCounter</string>
            <stringname="stop">StopCounter</string>
            </resources>

最后，我们还要在工程目录下放置一个编译脚本文件Android.mk：

                    LOCAL_PATH:=$(callmy-dir)
            include$(CLEAR_VARS)
            
            LOCAL_MODULE_TAGS:=optional
            
            LOCAL_SRC_FILES:=$(callall-subdir-java-files)
            
            LOCAL_PACKAGE_NAME:=Counter
            
                       include$(BUILD_PACKAGE)

接下来就要编译了。有关如何单独编译Android源代码工程的模块，以及如何打包system.img，请参考如何单独编译Android源代码中的模块一文。执行以下命令进行编译和打包：

                    USER-NAME@MACHINE-NAME:~/Android$mmmpackages/experimental/Counter
            USER-NAME@MACHINE-NAME:~/Android$makesnod

这样，打包好的Android系统镜像文件system.img就包含我们前面创建的Counter应用程序了。
再接下来，就是运行模拟器来运行我们的例子了。关于如何在Android源代码工程中运行模拟器，请参考在Ubuntu上下载、编译和安装Android最新源代码一文。执行以下命令启动模拟器：

                    USER-NAME@MACHINE-NAME:~/Android$emulator

最后我们就可以在Launcher中找到Counter应用程序图标，把它启动起来，点击Start按钮，就会看到应用程序界面上的计数器跑起来了：

这样，使用AsyncTask的例子就介绍完了，下面，我们就要根据上面对AsyncTask的使用情况来重点分析它的实现了。
AsyncTask类定义在frameworks/base/core/java/android/os/AsyncTask.java文件中：

                    publicabstractclassAsyncTask<Params,Progress,Result>{
            ......
            
            privatestaticfinalBlockingQueue<Runnable>sWorkQueue=
            newLinkedBlockingQueue<Runnable>(10);
            
            privatestaticfinalThreadFactorysThreadFactory=newThreadFactory(){
            privatefinalAtomicIntegermCount=newAtomicInteger(1);
            
            publicThreadnewThread(Runnabler){
            returnnewThread(r,"AsyncTask#"+mCount.getAndIncrement());
            }
            };
            
            ......
            
            privatestaticfinalThreadPoolExecutorsExecutor=newThreadPoolExecutor(CORE_POOL_SIZE,
            MAXIMUM_POOL_SIZE,KEEP_ALIVE,TimeUnit.SECONDS,sWorkQueue,sThreadFactory);
            
            privatestaticfinalintMESSAGE_POST_RESULT=0x1;
            privatestaticfinalintMESSAGE_POST_PROGRESS=0x2;
            privatestaticfinalintMESSAGE_POST_CANCEL=0x3;
            
            privatestaticfinalInternalHandlersHandler=newInternalHandler();
            
            privatefinalWorkerRunnable<Params,Result>mWorker;
            privatefinalFutureTask<Result>mFuture;
            
            ......
            
            publicAsyncTask(){
            mWorker=newWorkerRunnable<Params,Result>(){
            publicResultcall()throwsException{
            ......
            returndoInBackground(mParams);
            }
            };
            
            mFuture=newFutureTask<Result>(mWorker){
            @Override
            protectedvoiddone(){
            Messagemessage;
            Resultresult=null;
            
            try{
            result=get();
            }catch(InterruptedExceptione){
            android.util.Log.w(LOG_TAG,e);
            }catch(ExecutionExceptione){
            thrownewRuntimeException("AnerroroccuredwhileexecutingdoInBackground()",
            e.getCause());
            }catch(CancellationExceptione){
            message=sHandler.obtainMessage(MESSAGE_POST_CANCEL,
            newAsyncTaskResult<Result>(AsyncTask.this,(Result[])null));
            message.sendToTarget();
            return;
            }catch(Throwablet){
            thrownewRuntimeException("Anerroroccuredwhileexecuting"
            +"doInBackground()",t);
            }
            
            message=sHandler.obtainMessage(MESSAGE_POST_RESULT,
            newAsyncTaskResult<Result>(AsyncTask.this,result));
            message.sendToTarget();
            }
            };
            }
            
            ......
            
            publicfinalResultget()throwsInterruptedException,ExecutionException{
            returnmFuture.get();
            }
            
            ......
            
            publicfinalAsyncTask<Params,Progress,Result>execute(Params...params){
            ......
            
            mWorker.mParams=params;
            sExecutor.execute(mFuture);
            
            returnthis;
            }
            
            ......
            
            protectedfinalvoidpublishProgress(Progress...values){
            sHandler.obtainMessage(MESSAGE_POST_PROGRESS,
            newAsyncTaskResult<Progress>(this,values)).sendToTarget();
            }
            
            privatevoidfinish(Resultresult){
            ......
            onPostExecute(result);
            ......
            }
            
            ......
            
            privatestaticclassInternalHandlerextendsHandler{
            @SuppressWarnings({"unchecked","RawUseOfParameterizedType"})
            @Override
            publicvoidhandleMessage(Messagemsg){
            AsyncTaskResultresult=(AsyncTaskResult)msg.obj;
            switch(msg.what){
            caseMESSAGE_POST_RESULT:
            //Thereisonlyoneresult
            result.mTask.finish(result.mData[0]);
            break;
            caseMESSAGE_POST_PROGRESS:
            result.mTask.onProgressUpdate(result.mData);
            break;
            caseMESSAGE_POST_CANCEL:
            result.mTask.onCancelled();
            break;
            }
            }
            }
            
            privatestaticabstractclassWorkerRunnable<Params,Result>implementsCallable<Result>{
            Params[]mParams;
            }
            
            privatestaticclassAsyncTaskResult<Data>{
            finalAsyncTaskmTask;
            finalData[]mData;
            
            AsyncTaskResult(AsyncTasktask,Data...data){
            mTask=task;
            mData=data;
            }
            }
            }

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