I have a form activity every Edittext open another activity when I change data and I get it in my activity I lose the others that I have changed them before . this is initial state and this is what I get by changing any data.
You need a consistent data model in which to store those values. If it's size isn't larger than 2MB you can make this model Parcelable and seriali. After that you must cache those values either in savedInstanceState, SharedPrefs, singleton (I do not recommend it), or local DB (i.e. sqlite). After doing so, whenever your activity is displayed you should check if you already have a saved value for that field and fill it with that.
you can fix this by letting it open another fragment instead of activity and make sure that you dont destroy the activity.
so overall view you gonna have 1 main activity and each edit text will replace fragment view
Bonjour Flora
An activity is not supposed to be persisted if not displayed. That means it could stay as you left in when returning from another activity but it also may not.
If the system needs to free memory it will destroy the activity and recreate it when the user gets back to it. This is the expected behaviour on Android.
So what you should do is store your data when the activity goes out (in onPause() method) and fill your edittexts when the activity goes back in (in onResume() method)
Pay also attention that you need to handle what they call configuration change (such as screen rotation) using onConfigurationChanged() that allows you to pass some information between the former configuration and the latter for reuse.
Finally you should build your layout according to Android's guidelines (material design) for your UI to look a bit more conventional ;)
Related
Problem: Sometimes / on some devices the activity calling startActivityForResult (activity A) to launch activity B is being destroyed after calling startActivityForResult & before entering onActivityResult. We get a newly created instance of activity A to return to in onActivityResult - this causes our ViewModel (along with all other member variables) to be lost.
The standard thing to do would then be to restore the ui state using SavedInstanceState. This can't be done in this case due to the size of the object we need to restore - attempting this results in a TransactionTooLargeException. The ViewModel is too large for a Serializable or Parcelable.
Question: Is it possible to force our Activity to be kept intact during this workflow? Or is there another design that would let us avoid this problem? Saving any of the ViewModel's data to disk is not an option.
Context: This is a project where we store a list of images (as byte arrays) taken from the camera one at a time, and some related info about those images in a ViewModel. These are staged in a RecyclerView, where they can be uploaded when the user is done adding images. We add items to this ViewModel by calling startActivityForResult to launch a camera activity and return the resulting image.
We may only be seeing the problem of activity A getting destroyed due to the "Do not keep activities" setting in Developer Options being turned on, and this may not accurately represent how Android would reclaim resources (e.g. the conversation at the bottom of this thread - https://stackoverflow.com/questions/21227623/whats-the-main-advantage-and-disadvantage-of-do-not-keep-activities-in-android#:~:text=Android%20OS%20has%20this%20property,replicate%20the%20same%20scenario%20easily). Still, ideally we want everything to work with this setting on. Right now if activity A is destroyed, we lose our member variables and the ViewModel that we were in the process of building, and don't have a way to recover it.
Storing the ViewModel's data in a fragment (as discussed here: Fragment, save large list of data on onSaveInstanceState (how to prevent TransactionTooLargeException)) won't work since our activity is being destroyed, causing any associated fragments are as well. We actually have a fragment we're using in this way, which loads & holds a list of objects from the server to be selected from and associated with each image - this fragment ends up getting recreated along with the activity when its destroyed and then performs this load again.
No, what you want is not possible. If you launch another Activity using startActivityForResult() and that Activity requires resources, the launching Activity will be killed. There is nothing you can do to prevent this. It is standard Android behaviour and will happen, especially on low-end devices.
If your ViewModel is too large to save as the instance state, you will need to put the data somewhere else: SQLite database or a local file. Then store the name of the file or some key to the database as part of the saved instance state, and when the Activity is relaunched, restore the data from the file or data base.
Note: you shouldn't keep that much data in memory anyway, as you are wasting valuable resources. Only keep the data you really need in memory.
I have a fragment, which contains many EditTexts.
And when I rotate the device the EditText goes blank. The fragment is not saving its state/value. But at the same time if I use that fragment layout for activity it stores the EditText's state.
And yes I've given the IDs to each EditText, even to each view if that matters.
I know I can use saveInstanceState to save those values but is there any other way to do it? Cause there are almost 20 EdiText in that fragment, so should I use saveInstanceState, will it be okay to save these many variables/values in saveInstanceState?
Update:
I was recreating the fragment in activity on orientation change, so that was the reason, EditText was unable to save its state.
Such a silly mistake!
So now I just used saveInstanceState like following:
if (savedInstanceState == null) {
initialiseNewTaskFragment();
}
And that's it. EditText is saving its state now.
Thank you JorgeGil for saving my time!
Well this is a fairly loaded question lol.
So let's start with a few points.
First, you can of course handle your own lifecycle change if you choose to NOT allow Android to reset your lifecycle on device rotate.
android:configChanges="orientation"
Use that flag in your manifest if you want to retain everything and handle your own rotation changes. However, if you have a layout-land folder with different XML files, you will not want to do this.
Yes of course you can do fragment.retainInstance when nested in Activities to get it to retain values. However, retaining populated Elements with values is not something you can just natively expect it to do as the UI elements were completely redrawn, so something has to tell it to redraw it again.
So if you are going old school and you are actually still doing findViewById and myText.setText('some Stuff'). Then you may find some time savings in using a library like icepick.
https://github.com/frankiesardo/icepick
However, the BEST option by a mile is to modernize your coding practice to use DataBinding. This allows you to not care about the UI interactions anymore as the values are bound to your Fragment or Activity or Model values by default and can be done with 2-way binding. This ensures databinding always populates with the value that was last updated.
Imagine you have an object of
public class Student implements BaseObservable{
String firstName;
}
Then in your xml you have
editText
android:text="#={student.firstName}"
Obviously there is a little more, like you need to set your student object in the onCreate to ensure it is in the XML for using. But when the user modifies the student firstname it is retained in the model, and redrawn automatically into the Edit Text.
This is your best solution, but depends on how invested you are in the future binding techniques of Android development or if you just prefer to go status quo to get across a finish line.
Hope that helps.
Add this in your Activity tag on your AndroidManifest.xml to avoid the recreation of the Activity and you won't lose the data.
android:configChanges="orientation|screenSize"
Before I begin, I have read this, this and some more articles online. I am still unable to find a right way to do it.
So I have just one activity in my App, and 6 fragments. First one is a ListFragment which loads a list from a SQLite table. When user taps on a row in this list, I do 2 things:
1) Get an int from that row through a listener, and pass it back to the parent activity which stores it as a class variable using a simple setter method.
2) Replace this ListFragment with another simple Fragment. This new Fragment uses a simple getter() on that class variable to retrieve some information from a different table, and show all the details to the user.
So far so good. Now if I am on this details Fragment, and I change the screen orientation, the activity state is not reloaded (as I am checking if savedInstanceState is null in the onCreate()), but however, the class variables lose their value, and my app crashes.
Basically I am trying to pass data from the ListFragment to the details Fragment. I am doing it through the activity, which is causing a problem. As per Android Documentation:
All Fragment-to-Fragment communication is done through the associated
Activity. Two Fragments should never communicate directly.
There is no specific code which is giving me trouble, so didn't post any.
The onSaveInstanceState and onRestoreInstanceState is only used to save and restore per-instance state of an activity in case your activity is destroyed by OS (for example, to free the memory or in order to recreate it when the device orientation was changed). So you can save your variable in onSaveInstanceState and get them back using onRestoreInstanceState.
For your next question, I think this article will help you. Also answer by Gene for this question will help you.
I have a tabhost in my first activity and Im calling another activity sometimes; to handle some details. I need to remember the last tab selected in my first activity when the second one returns. Problem is the first activity is getting destroyed and created again and onSaveInstanceState is not getting called. The only option which I can think of is to write the last tab selected to external memory and read it back, which seems a little extreme considering this is just one tag. Is there any other option? I cant avoid the second activity (I had tried to change that to another fragment--fragment calling another fragment-- but that didn't work so well for me)
Cheers
If you want to save small amounts of data in Android, you can always use SharedPreferences. Here is a good example on how to use it.
And there are some other storage options for Android listed here
Is it possible to add a textView on Activity B without showing it?
What I mean is, when i press a button (on DiallerActivity), then a textView will be added on HistoryActivity without leaving DiallerActivity.
How can I do this?
is it possible to a add textView on Activity B without show it ?
No, not directly.
An Activity is a special case Android class and shouldn't be treated as a normal Java class. Effectively the purpose of an Activity is to act as a framework for a UI so, if an Activity isn't visible then there basically is no UI. In other words, how can something be a user-interface if the user isn't able to see or interact with it?
As logical Chimp suggests, the changes should be with respect to some form of data history (a database or SharedPreferences) and it is the responsibility of your HistoryActivity to update its visual elements (TextViews) next time it is started.
One Activity shouldn't try to modify the look, feel or behaviour of another Activity except indirectly by changing some form of global data or state or by passing data to it if the first Activity is responsible for starting the second.
hmmm - not sure I fully understand your question. Are you wanting to append the dialled number to the 'HistoryActivity' without showing it?
If so, I suggest you separate your data (list of dialled numbers) from the view (HistoryActivity). Then, you only have to add the dialled number to the data record used to hold them (suggest a list). When the user opens the HistoryActivity, then you can just draw as many text fields as required to display the data.