How to handle screen orientation change when progress dialog and background thread active?
My program does some network activity in a background thread. Before starting, it pops up a progress dialog. The dialog is dismissed on the handler. This all works fine, except when screen orientation changes while the dialog is up (and the background thread is going). At this point the app either crashes, or deadlocks, or gets into a weird stage where the app does not work at all until all the threads have been killed.
How can I handle the screen orientation change gracefully?
The sample code below matches roughly what my real program does:
public class MyAct extends Activity implements Runnable {
public ProgressDialog mProgress;
// UI has a button that when pressed calls send
public void send() {
mProgress = ProgressDialog.show(this, "Please wait",
"Please wait",
true, true);
Thread thread = new Thread(this);
thread.start();
}
public void run() {
Thread.sleep(10000);
Message msg = new Message();
mHandler.sendMessage(msg);
}
private final Handler mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
mProgress.dismiss();
}
};
}
Stack:
E/WindowManager( 244): Activity MyAct has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@433b7150 that was originally added here
E/WindowManager( 244): android.view.WindowLeaked: Activity MyAct has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@433b7150 that was originally added here
E/WindowManager( 244): at android.view.ViewRoot.<init>(ViewRoot.java:178)
E/WindowManager( 244): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:147)
E/WindowManager( 244): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:90)
E/WindowManager( 244): at android.view.Window$LocalWindowManager.addView(Window.java:393)
E/WindowManager( 244): at android.app.Dialog.show(Dialog.java:212)
E/WindowManager( 244): at android.app.ProgressDialog.show(ProgressDialog.java:103)
E/WindowManager( 244): at android.app.ProgressDialog.show(ProgressDialog.java:91)
E/WindowManager( 244): at MyAct.send(MyAct.java:294)
E/WindowManager( 244): at MyAct$4.onClick(MyAct.java:174)
E/WindowManager( 244): at android.view.View.performClick(View.java:2129)
E/WindowManager( 244): at android.view.View.onTouchEvent(View.java:3543)
E/WindowManager( 244): at android.widget.TextView.onTouchEvent(TextView.java:4664)
E/WindowManager( 244): at android.view.View.dispatchTouchEvent(View.java:3198)
I have tried to dismiss the progress dialog in onSaveInstanceState, but that just prevents an immediate crash. The background thread is still going, and the UI is in partially drawn state. Need to kill the whole app before it starts working again.
When you switch orientations, Android will create a new View. You're probably getting crashes because your background thread is trying to change the state on the old one. (It may also be having trouble because your background thread isn't on the UI thread)
I'd suggest making that mHandler volatile and updating it when the orientation changes.
Edit: Google engineers do not recommend this approach, as described by Dianne Hackborn (aka hackbod) in this StackOverflow post . Check out this blog post for more information.
You have to add this to the activity declaration in the manifest:
android:configChanges="orientation|screenSize"
so it looks like
<activity android:label="@string/app_name"
android:configChanges="orientation|screenSize|keyboardHidden"
android:name=".your.package">
The matter is that the system destroys the activity when a change in the configuration occurs. See ConfigurationChanges.
So putting that in the configuration file avoids the system to destroy your activity. Instead it invokes the onConfigurationChanged(Configuration) method.
I came up with a rock-solid solution for these issues that conforms with the 'Android Way' of things. I have all my long-running operations using the IntentService pattern.
That is my activities broadcast intents, the IntentService does the work, saves the data in the DB and then broadcasts STICKY intents.
The sticky part is important, such that even if the Activity was paused during during the time after the user initiated the work and misses the real time broadcast from the ItentService we can still respond and pick up the data from the calling Activity.
ProgressDialogs can work into this pattern quite nicely with onSaveInstanceSate() .
Basically, you need to save a flag that you have a progress dialog running in the saved instance bundle. DO NOT save the progress dialog object because this will leak the entire Activity.
To have a persistent handle to the progress dialog, I store it as a Weak-reference in the application object.
On orientation change or any thing else that causes the Activity to pause (phone call, user hits home etc) and then resume, I dismiss the old dialog and recreate a new dialog in the newly created Activity.
For indefinite progress dialogs this is easy. For progress bar style, you have to put the last known progress in the bundle and whatever information you're using locally in the activity to keep track of the progress.
On restore the progress, you'll use this information to re-spawn the progress bar in the same state as before and then update based on the current state of things.
So to summarize, putting long-running tasks into an IntentService coupled with juidcious use of onSaveInstanceState() allows you to efficiently keep track of dialogs and restore then across the Activity life-cycle events. Relevant bits of Activity code are below. You'll also need logic in your BroadcastReceiver to handle Sticky intents appropriately, but that is beyond the scope of this.
public void doSignIn(View view) {
waiting=true;
AppClass app=(AppClass) getApplication();
String logingon=getString(R.string.signon);
app.Dialog=new WeakReference<ProgressDialog>(ProgressDialog.show(AddAccount.this, "", logingon, true));
..}
@Override
protected void onSaveInstanceState(Bundle saveState) {
super.onSaveInstanceState(saveState);
saveState.putBoolean("waiting",waiting);
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if(savedInstanceState!=null) {
restoreProgress(savedInstanceState);
}
...}
private void restoreProgress(Bundle savedInstanceState) {
waiting=savedInstanceState.getBoolean("waiting");
if (waiting) {
AppClass app=(AppClass) getApplication();
ProgressDialog refresher=(ProgressDialog) app.Dialog.get();
refresher.dismiss();
String logingon=getString(R.string.signon);
app.Dialog=new WeakReference<ProgressDialog>(ProgressDialog.show(AddAccount.this, "", logingon, true));
}
}
上一篇: 使用排球时，活动已经泄露了窗口