Android : Save application state on screen orientation change - android

I have seen the following links before posting this question
http://www.devx.com/wireless/Article/40792/1954
Saving Android Activity state using Save Instance State
http://www.gitshah.com/2011/03/how-to-handle-screen-orientation_28.html
How to save state during orientation change in Android if the state is made of my classes?
I am not getting how should i override the following function :
#Override
public Object onRetainNonConfigurationInstance() {
return someExpensiveObject;
}
In my application i have layout with one editext visible and other editext get visible when the data of first editext validates to true.I have set the visbility of all other editextes and textviews to false and make them visible after validating.
So in my activity if the screen orientation is changed then all the items having android:visibility="false" get invisible.
I have also came to know that when our activities screen orientation changes it calls onStop() followed by onDestroy() and then again starts a fresh activity by calling onCreate()
This is the cause .. But i am not getting how to resolve it ..
Here You can see the screenshots of my application :
in this image all fields are loaded
and in another image when the screen orientation is changed to landscape they are all gone
Any link to tutorial or piece of code will be highly appreciable.
And also my application crashes when a progress dialog is shown up and i try to change screen orientation.How to handle this ??
Thanks

Well if you have the same layout for both screens then there is no need to do so just add below line in your manifest in Activity node
android:configChanges="keyboardHidden|orientation"
for Android 3.2 (API level 13) and newer:
android:configChanges="keyboardHidden|orientation|screenSize"
because the "screen size" also changes when the device switches between portrait and landscape orientation.
From documentation here: http://developer.android.com/guide/topics/manifest/activity-element.html

There is another possibility using which you can keep the state as it is even on Orientation change using the onConfigurationChanged(Configuration newConfig).
Called by the system when the device configuration changes while your activity is running. Note that this will only be called if you have selected configurations you would like to handle with the configChanges attribute in your manifest. If any configuration change occurs that is not selected to be reported by that attribute, then instead of reporting it the system will stop and restart the activity (to have it launched with the new configuration).
At the time that this function has been called, your Resources object will have been updated to return resource values matching the new configuration.

There are 2 ways of doing this, the first one is in the AndroidManifest.xml file. You can add this to your activity's tag. This documentation will give you an in depth explanation, but put simply it uses these values and tells the activity not to restart when one of these values changes.
android:configChanges="keyboardHidden|orientation|screenSize|screenLayout"
And the second one is: overriding onSaveInstanceState and onRestoreInstanceState. This method requires some more effort, but arguably is better. onSaveInstanceState saves the values set (manually by the developer) from the activity before it's killed, and onRestoreInstanceState restores that information after onStart() Refer to the official documentation for a more in depth look. You don't have to implement onRestoreInstanceState, but that would involve sticking that code in onCreate().
In my sample code below, I am saving 2 int values, the current position of the spinner as well as a radio button.
#Override
public void onSaveInstanceState(#NonNull Bundle savedInstanceState) {
spinPosition = options.getSelectedItemPosition();
savedInstanceState.putInt(Constants.KEY, spinPosition);
savedInstanceState.putInt(Constants.KEY_RADIO, radioPosition);
super.onSaveInstanceState(savedInstanceState);
}
// And we restore those values with `getInt`, then we can pass those stored values into the spinner and radio button group, for example, to select the same values that we saved earlier.
#Override
public void onRestoreInstanceState(#NotNull Bundle savedInstanceState) {
spinPosition = savedInstanceState.getInt(Constants.KEY);
radioPosition = savedInstanceState.getInt(Constants.KEY_RADIO);
options.setSelection(spinPosition, true);
type.check(radioPosition);
super.onRestoreInstanceState(savedInstanceState);
}

Related

Device Orientation Destroy Activity

I've got my app working for the most part, but I've got buttons and text views with text that change based on some state variables. When I change the device's orientation it destroys and recreates the activity in the new orientation. I've tried adding
android:configChanges="orientation"
to the manifest file. I've also tried overriding the onConfigurationChanges method to "do nothing" but the text still reverts to default.
I know I can lock the user in to one orientation, but I would rather have the app usable in either orientation.
Alternatively, is there a way to determine which orientation the user opened the app in and lock them in that orientation until they restart the app?
Edit:
Thank you Kabir,
android:configChanges="orientation|screenSize"
works perfectly
For API 12 and below:
android:configChanges="orientation"
if you are targeting API 13 or above
android:configChanges="orientation|screenSize"
Actually orientation changing works by destroying and recreating an activity. Some views are able to save theirs states, others no. TextView doesn't save its state (in this case text) as it tends to show static text. If you want to save TextView's state during the configuration changes, you can do as following:
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
/*
1st argument is key, 2nd is value to save
*/
outState.putString("savedText", myTextView.getText().toString());
}
#Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
/*
The argument is key to get saved string
*/
myTextView.setText(savedInstanceState.getString("savedText"));
}
These onSaveInstanceState() and onRestoreInstanceState() are Activiy's methods.

Android save state on orientation change

I've got an Android application which maintains state regarding distance traveled, time elapsed, etc. This state I can conveniently store in an object and store a reference to that object in the Bundle when Android calls onDestroy() when the user changes the screen orientation, then restore the state in onCreate(Bundle savedBundle). However, I also have some state in the Buttons and EditText objects on the screen that I want to persist through screen orientations. For example, in onStart(Bundle savedBundle) I call:
_timerButton.setBackgroundColor(Color.GREEN);
_pauseButton.setBackgroundColor(Color.YELLOW);
_pauseButton.setEnabled(false);
Then throughout the operation of my app, the colors/enabled status of these buttons will be changed. Is there a more convenient way to persist the state of user interface items (EditText, Button objects, etc) without having to manually save/restore each attribute for each button? It feels really clumsy to have to manually manage this type of state in between screen orientations.
Thanks for any help.
Add android:configChanges in the Manifest file
<activity name= ".MainActivity"
android:configChanges="orientation|screenSize"/>
By default, this does not work because changing the orientation causes the onCreate method to be called again and redraws the view.
However, if this parameter is included, the framework will handle preserving the state of the screen or layout if the orientation is changed.
Refer following official documentation for more info:
Activity Lifecycle
Handling configuration changes
To save your variable or values you should use onSaveInstanceState(Bundle); and when orientation changes then should recover values should use onRestoreInstanceState() as well, but not very common. (onRestoreInstanceState() is called after onStart(), whereas onCreate() is called before onStart().
Use the put methods to store values in onSaveInstanceState()
protected void onSaveInstanceState(Bundle icicle) {
super.onSaveInstanceState(icicle);
icicle.putLong("param", value);
}
And restore the values in onCreate():
public void onCreate(Bundle icicle) {
if (icicle != null){
value = icicle.getLong("param");
}
}

Maintaining Progress Bar Visibility with Orientation Change

I have a progress bar (swirly waiting style) defined in xml as:
<ProgressBar
android:layout_width="wrap_content"
android:layout_height="wrap_content"
style="#android:style/Widget.Holo.ProgressBar.Large"
android:layout_centerVertical="true"
android:layout_centerHorizontal="true"
android:id="#+id/progress"
/>
I hide it's visibility in the activity's onCreate method using,
progressBar.setVisibility(View.GONE);
and start it on a button's onClick event using
progressBar.setVisibility(View.VISIBLE);
Now if I change the screen oreintation the progress bar disappears. I understand that the activity is destroyed and recreated on an orientation change, and the state of the activity is recreated in the new orientation from the saved Bundle savedInstanceState. So am I right in thinking that the default Bundle saved by android does not include any changes made to to a ProgressBar View object?
If this is the case, is it correct to say that the only way to reinstate the correct visibility of the ProgressBar after an orientation change is to save a flag (e.g. boolean pbState = false/true) by overriding the method onSaveInstanceState and inspecting this flag in onRestoreInstanceState and setting the visibility accordingly? Or, am I missing something really obvious about saving the state of view objects.
Thanks
UPDATE:
Both the solutions provided below work. I decided to opt for putting android:configChanges="orientation|screenSize" in the manifest xml file. However, the documentation states that this method should only be used as a last resort. My activity is fairly simple, and so the manifest xml method reduces the amount of code required in the main activity, i.e., no onRestoreInstanceState method. I presume if you're activity is more complex, you'll probably want to explicitly define any state changes using the latter method.
So am I right in thinking that the default Bundle saved by android
does not include any changes made to to a ProgressBar View object?
You are right. Android will not save the state of progressBar, or any other widget for that matter.
[Is] it correct to say that the only way to reinstate the correct
visibility of the ProgressBar after an orientation change is to save a
flag (e.g. boolean pbState = false/true) by overriding the method
onSaveInstanceState and inspecting this flag in onRestoreInstanceState
and setting the visibility accordingly?
Absolutely. About onRestoreInstanceState(Bundle): You can do without overriding this method. To confirm orientation change, check for savedInstanceState ==> Bundle passed to onCreate(Bundle) against null. If an orientation change has occurred, savedInstanceState will not be null. On start of an activity, savedInstanceState will be null. Following code (which is basically what you proposed) should do the job:
Declare a global boolean variable:
boolean progressBarIsShowing;
In your onCreate(Bundle):
// savedInstanceState != null ===>>> possible orientation change
if (savedInstanceState != null && savedInstanceState.contains("progressbarIsShowing")) {
// If `progressBarIsShowing` was stored in bundle, `progressBar` was showing
progressBar.setVisibility(View.VISIBLE);
} else {
// Either the activity was just created (not recreated), or `progressBar` wasn't showing
progressBar.setVisibility(View.GONE);
}
Whenever you show progressBar, set progressBarIsShowing to true. And toggle it when you dismiss progressBar.
Override onSaveInstanceState(Bundle):
if (progressBarIsShowing) {
outState.putBoolean("progressBarIsShowing", progressBarIsShowing);
}
Caution: Check for when user browses away from your activity(via home button press etc). You might get a BadTokenException if progressBar is showing when the user does so.
You use the following line inside your activity tag in manifest.
<activity android:name="your activity"
android:configChanges="keyboard|keyboardHidden|orientation|screenLayout|uiMode|screenSize|smallestScreenSize"/>
In the above android:configChanges="orientation" will maintain the state of your application while configuration change.
Using android:configChanges is bad practice, because it might get you in much worse trouble.
Also saving a variable at onSaveInstanceState didn't work for me, since you won't get updates while the Activity is destroyed.
I ended up using a ResultReceiver inside a Fragment that doesn't get destroyed by using setRetainInstance(true).
A good article concerning this problem can be found here:
https://www.androiddesignpatterns.com/2013/04/retaining-objects-across-config-changes.html
Also see my answer here: https://stackoverflow.com/a/54334864/6747171

App resets values when I turn device to side

I have an app that adds to a total variable when a button is clicked.
However if I turn my phone so the layout gets turned into the horizontal layout the values all get reset, and idea why this is and how to stop it?
Thanks!
When you move your device, your device's Orientation State changes from Portrait to Landscape of from Lanscape to Portrait.
In this Orientation change, your Activity's onCreate Method is called every time.
Therefore the values in your Activity are being reset.
There are 2 ways of solving this problem:
1) Let You Activity manage it for you.
2) Managing the changes yourself by saving and restoring states.
Using 1st way of solving this problem:
Just add this line in your Activity Node in your Manifest.xml file.
android:configChanges="orientation|keyboardHidden|screenSize"
For example:
<activity
android:name=".MyMainActivity"
android:configChanges="orientation|keyboardHidden|screenSize"
android:label="#string/app_name" >
Using the second Way:
You can override these two Methods:
public void onSaveInstanceState(Bundle bundle) {
super.onSaveInstanceState(bundle);
//Manage your Data Explicitly here.
}
public void onRestoreInstanceState(Bundle bundle) {
super.onRestoreInstanceState(bundle);
//Manage your Data Explicitly here.
}
EDITAccording to Android Dev Guide:
Using android:configChanges="orientation|keyboardHidden|screenSize" is not a good practice.
Quote from this page
Note: Using this attribute should be avoided and used only as a last resort. Please read Handling Runtime Changes for more information about how to properly handle a restart due to a configuration change.
I recommend you to follow the Android Dev Guide for Handling Run-time Changes and follow the good Practices.
you need to save the variable in OnSaveInstanceState and restore it in onRestoreInstnace state
For example;
#Override
public void onSaveInstanceState(Bundle bundle) {
bundle.putParcelableArrayList(PEOPLE, people);
super.onSaveInstanceState(bundle);
}
#Override
public void onRestoreInstanceState(Bundle bundle) {
super.onRestoreInstanceState(bundle);
people = bundle.getParcelableArrayList(PEOPLE);
}
This happens because the normal way Android handles an activity during any configuration change (including screen reorientations) is to destroy the activity and recreate it. As described in the guide topic Handling Runtime Changes, you can handle it a couple of ways. The "Android way" is to save your activity's state information by overriding onSaveInstanceState and onRestoreInstanceState methods. The details about how to use these methods can be found in the guide topic Recreating an Activity.
The other way to prevent this problem is to tell Android that your activity will handle configuration changes internally. You do this by adding android:configChanges="orientation" to the <activity> tag in the manifest for the activity and overriding the onConfigurationChanged method of the activity to actually handle the changes.

how to retain the state of activity in android

How do I retain the state of an activity in android? I have two layouts for portrait and landscape in layout and layout-land. I am loading the value from service at the time I am showing progress dialog. If loaded user rotates the device to landscape at the time also loading. How do I avoid that? user typed content in webview that also refreshed. How do I avoid that, can anybody provide an example?
Thanks
When orientation changes, the Activity is reloaded by default. If you do not want this behavior then add this to the Activity definition in your manifest:
android:configChanges="orientation|keyboardHidden"
For more detail, see Handling Runtime Changes
You can use the onRetainNonConfigurationChange() callback to store arbitrary data. It is called just before your application is about to be recreated.
Then, in onCreate() just check if some data were put aside by calling getLastNonConfigurationInstance() that returns the Object you put aside or null.
See this article on android developers.
Here's a sample borrowed from the link above:
#Override
public Object onRetainNonConfigurationInstance() {
//this is called by the framework when needed
//Just return what you want to save here.
return MyBigObjectThatContainsEverythingIWantToSave;
}
Automagic restore of previously saved state:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
final MyDataObject MyBigObjectThatContainsEverythingIWantToSave = (MyDataObject) getLastNonConfigurationInstance();
if (MyBigObjectThatContainsEverythingIWantToSave == null) {
//No saved state
MyBigObjectThatContainsEverythingIWantToSave = loadMyData();
} else {
//State was restored, no need to download again.
}
...
}
When orientation changes, the Activity is reloaded by default. If you do not want this behavior then add this to the Activity definition in your android manifest file :
android:configChanges="orientation|screenSize|keyboardHidden"

Categories

Resources