接下來我們再看看應用程式的配置檔案AndroidManifest.xml：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="shy.luo.counter"
android:versionCode="1"
android:versionName="1.0">
<application android:icon="@drawable/icon" android:label="@string/app_name">
<activity android:name=".Counter"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
這個配置檔案很簡單，我們就不介紹了。
再來看應用程式的界面檔案，它定義在res/layout/main.xml檔案中：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns: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>
android:id="@+id/textview_counter"
android:text="0">
</LinearLayout>
<Button
android:id="@+id/button_start"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/start">
</Button>
android:id="@+id/button_stop"
android:text="@string/stop" >
</LinearLayout>
</LinearLayout>
這個界面配置檔案也很簡單，等一下我們在模拟器把這個應用程式啟動起來後，就可以看到它的截圖了。應用程式用到的字元串資源檔案位于res/values/strings.xml檔案中：
<resources>
<string name="app_name">Counter</string>
<string name="counter">Counter: </string>
<string name="start">Start Counter</string>
<string name="stop">Stop Counter</string>
</resources>
最後，我們還要在工程目錄下放置一個編譯腳本檔案Android.mk：
LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE_TAGS := optional
LOCAL_SRC_FILES := $(call all-subdir-java-files)
LOCAL_PACKAGE_NAME := Counter
include $(BUILD_PACKAGE)
執行以下指令進行編譯和打包：
USER-NAME@MACHINE-NAME:~/Android$ mmm packages/experimental/Counter
USER-NAME@MACHINE-NAME:~/Android$ make snod
這樣，打包好的Android系統鏡像檔案system.img就包含我們前面建立的Counter應用程式了。
執行以下指令啟動模拟器：
USER-NAME@MACHINE-NAME:~/Android$ emulator
這樣，使用AsyncTask的例子就介紹完了，下面，我們就要根據上面對AsyncTask的使用情況來重點分析它的實作了。
AsyncTask類定義在frameworks/base/core/java/android/os/AsyncTask.java檔案中：
public abstract class AsyncTask<Params, Progress, Result> {
......
private static final BlockingQueue<Runnable> sWorkQueue =
new LinkedBlockingQueue<Runnable>(10);
private static final ThreadFactory sThreadFactory = new ThreadFactory() {
private final AtomicInteger mCount = new AtomicInteger(1);
public Thread newThread(Runnable r) {
return new Thread(r, "AsyncTask #" + mCount.getAndIncrement());
}
};
private static final ThreadPoolExecutor sExecutor = new ThreadPoolExecutor(CORE_POOL_SIZE,
MAXIMUM_POOL_SIZE, KEEP_ALIVE, TimeUnit.SECONDS, sWorkQueue, sThreadFactory);
private static final int MESSAGE_POST_RESULT = 0x1;
private static final int MESSAGE_POST_PROGRESS = 0x2;
private static final int MESSAGE_POST_CANCEL = 0x3;
private static final InternalHandler sHandler = new InternalHandler();
private final WorkerRunnable<Params, Result> mWorker;
private final FutureTask<Result> mFuture;
public AsyncTask() {
mWorker = new WorkerRunnable<Params, Result>() {
public Result call() throws Exception {
......
return doInBackground(mParams);
}
};
mFuture = new FutureTask<Result>(mWorker) {
@Override
protected void done() {
Message message;
Result result = null;
try {
result = get();
} catch (InterruptedException e) {
android.util.Log.w(LOG_TAG, e);
} catch (ExecutionException e) {
throw new RuntimeException("An error occured while executing doInBackground()",
e.getCause());
} catch (CancellationException e) {
message = sHandler.obtainMessage(MESSAGE_POST_CANCEL,
new AsyncTaskResult<Result>(AsyncTask.this, (Result[]) null));
message.sendToTarget();
return;
} catch (Throwable t) {
throw new RuntimeException("An error occured while executing "
+ "doInBackground()", t);
}
message = sHandler.obtainMessage(MESSAGE_POST_RESULT,
new AsyncTaskResult<Result>(AsyncTask.this, result));
message.sendToTarget();
}
public final Result get() throws InterruptedException, ExecutionException {
return mFuture.get();
public final AsyncTask<Params, Progress, Result> execute(Params... params) {
......
mWorker.mParams = params;
sExecutor.execute(mFuture);
return this;
protected final void publishProgress(Progress... values) {
sHandler.obtainMessage(MESSAGE_POST_PROGRESS,
new AsyncTaskResult<Progress>(this, values)).sendToTarget();
private void finish(Result result) {
onPostExecute(result);
private static class InternalHandler extends Handler {
@SuppressWarnings({"unchecked", "RawUseOfParameterizedType"})
@Override
public void handleMessage(Message msg) {
AsyncTaskResult result = (AsyncTaskResult) msg.obj;
switch (msg.what) {
case MESSAGE_POST_RESULT:
// There is only one result
result.mTask.finish(result.mData[0]);
break;
case MESSAGE_POST_PROGRESS:
result.mTask.onProgressUpdate(result.mData);
case MESSAGE_POST_CANCEL:
result.mTask.onCancelled();
private static abstract class WorkerRunnable<Params, Result> implements Callable<Result> {
Params[] mParams;
private static class AsyncTaskResult<Data> {
final AsyncTask mTask;
final Data[] mData;
AsyncTaskResult(AsyncTask task, Data... data) {
mTask = task;
mData = data;
}
本文轉自 Luoshengyang 51CTO部落格，原文連結：http://blog.51cto.com/shyluo/966885，如需轉載請自行聯系原作者
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