Android：后台处理/异步配置更改
要在后台进程中保持异步状态，您可以使用片段帮助。
请参阅以下步骤：
步骤1：创建一个无标题的片段，让它说是后台任务，并在其中添加一个私有的异步任务类。
第2步（可选步骤）：如果要将加载光标置于活动顶部，请使用以下代码：
步骤3：在主要的Activity中，实现步骤1中定义的BackgroundTaskCallbacks接口
class BackgroundTask extends Fragment {
public BackgroundTask() {
}
static interface BackgroundTaskCallbacks {
void onPreExecute();
void onCancelled();
void onPostExecute();
void doInBackground();
}
private BackgroundTaskCallbacks callbacks;
private PerformAsyncOpeation asyncOperation;
private boolean isRunning;
private final String TAG = BackgroundTask.class.getSimpleName();
public void start() {
Log.d(TAG, "********* BACKGROUND TASK START OPERATION ENTER *********");
if (!isRunning) {
asyncOperation = new PerformAsyncOpeation();
asyncOperation.execute();
isRunning = true;
}
Log.d(TAG, "********* BACKGROUND TASK START OPERATION EXIT *********");
}
public void cancel() {
Log.d(TAG, "********* BACKGROUND TASK CANCEL OPERATION ENTER *********");
if (isRunning) {
asyncOperation.cancel(false);
asyncOperation = null;
isRunning = false;
}
Log.d(TAG, "********* BACKGROUND TASK CANCEL OPERATION EXIT *********");
}
public boolean isRunning() {
return isRunning;
}
public void onAttach(Activity activity) {
Log.d(TAG, "********* BACKGROUND TASK ON ATTACH ENTER *********");
super.onAttach(activity);
if (!(activity instanceof BackgroundTaskCallbacks)) {
throw new IllegalStateException(
"Activity must implement the LoginCallbacks interface.");
}
callbacks = (BackgroundTaskCallbacks) activity;
Log.d(TAG, "********* BACKGROUND TASK ON ATTACH EXIT *********");
}
public void onCreate(Bundle savedInstanceState) {
Log.d(TAG, "********* BACKGROUND TASK ON CREATE ENTER *********");
super.onCreate(savedInstanceState);
setRetainInstance(true);
Log.d(TAG, "********* BACKGROUND TASK ON CREATE EXIT *********");
}
public void onDetach() {
super.onDetach();
callbacks = null;
}
private class PerformAsyncOpeation extends AsyncTask<Void, Void, Void> {
protected void onPreExecute() {
Log.d(TAG,
"********* BACKGROUND TASK :-> ASYNC OPERATION :- > ON PRE EXECUTE ENTER *********");
if (callbacks != null) {
callbacks.onPreExecute();
}
isRunning = true;
Log.d(TAG,
"********* BACKGROUND TASK :-> ASYNC OPERATION :- > ON PRE EXECUTE EXIT *********");
}
protected Void doInBackground(Void... params) {
Log.d(TAG,
"********* BACKGROUND TASK :-> ASYNC OPERATION :- > DO IN BACKGROUND ENTER *********");
if (callbacks != null) {
callbacks.doInBackground();
}
Log.d(TAG,
"********* BACKGROUND TASK :-> ASYNC OPERATION :- > DO IN BACKGROUND EXIT *********");
return null;
}
protected void onCancelled() {
Log.d(TAG,
"********* BACKGROUND TASK :-> ASYNC OPERATION :- > ON CANCEL ENTER *********");
if (callbacks != null) {
callbacks.onCancelled();
}
isRunning = false;
Log.d(TAG,
"********* BACKGROUND TASK :-> ASYNC OPERATION :- > ON CANCEL EXIT *********");
}
protected void onPostExecute(Void ignore) {
Log.d(TAG,
"********* BACKGROUND TASK :-> ASYNC OPERATION :- > ON POST EXECUTE ENTER *********");
if (callbacks != null) {
callbacks.onPostExecute();
}
isRunning = false;
Log.d(TAG,
"********* BACKGROUND TASK :-> ASYNC OPERATION :- > ON POST EXECUTE EXIT *********");
}
}
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
setRetainInstance(true);
}
public void onStart() {
super.onStart();
}
public void onResume() {
super.onResume();
}
public void onPause() {
super.onPause();
}
public void onStop() {
super.onStop();
}
public class ProgressIndicator extends Dialog {
public ProgressIndicator(Context context, int theme) {
super(context, theme);
}
private ProgressBar progressBar;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.progress_indicator);
this.setCancelable(false);
progressBar = (ProgressBar) findViewById(R.id.progressBar);
progressBar.getIndeterminateDrawable().setColorFilter(R.color.DarkBlue, android.graphics.PorterDuff.Mode.SCREEN);
}
@Override
public void show() {
super.show();
}
@Override
public void dismiss() {
super.dismiss();
}
@Override
public void cancel() {
super.cancel();
}
public class MyActivity extends FragmentActivity implements BackgroundTaskCallbacks,{
private static final String KEY_CURRENT_PROGRESS = "current_progress";
ProgressIndicator progressIndicator = null;
private final static String TAG = MyActivity.class.getSimpleName();
private BackgroundTask task = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(
initialize your views and widget here .............
FragmentManager fm = getSupportFragmentManager();
task = (BackgroundTask) fm.findFragmentByTag("login");
if (task == null) {
task = new BackgroundTask();
fm.beginTransaction().add(task, "login").commit();
}
if (savedInstanceState != null) {
Log.i(TAG, "KEY_CURRENT_PROGRESS_VALUE ON CREATE :: "
+ task.isRunning());
if (task.isRunning()) {
progressIndicator = new ProgressIndicator(this,
R.style.TransparentDialog);
if (progressIndicator != null) {
progressIndicator.show();
}
}
}
}
@Override
protected void onPause() {
super.onPause();
}
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
Log.i(TAG, "KEY_CURRENT_PROGRESS_VALUE ON SAVE INSTANCE :: "
+ task.isRunning());
outState.putBoolean(KEY_CURRENT_PROGRESS, task.isRunning());
if (progressIndicator != null) {
progressIndicator.dismiss();
progressIndicator.cancel();
}
progressIndicator = null;
}
private void performOperation() {
if (!task.isRunning() && progressIndicator == null) {
progressIndicator = new ProgressIndicator(this,
R.style.TransparentDialog);
progressIndicator.show();
}
if (task.isRunning()) {
task.cancel();
} else {
task.start();
}
}
@Override
protected void onDestroy() {
super.onDestroy();
if (progressIndicator != null) {
progressIndicator.dismiss();
progressIndicator.cancel();
}
progressIndicator = null;
}
@Override
public void onPreExecute() {
Log.i(TAG, "CALLING ON PRE EXECUTE");
}
@Override
public void onCancelled() {
Log.i(TAG, "CALLING ON CANCELLED");
if (progressIndicator != null) {
progressIndicator.dismiss();
progressIndicator.cancel();
}
public void onPostExecute() {
Log.i(TAG, "CALLING ON POST EXECUTE");
if (progressIndicator != null) {
progressIndicator.dismiss();
progressIndicator.cancel();
progressIndicator = null;
}
}
@Override
public void doInBackground() {
}
}
setRetainInstance(true)实际上有帮助的信息。