Develop Reference

Have Activity A and B in activity

I Have Activity A and B. In activity A , I load data then when click on the list it move me to activity B. When go back to activity A the data load again. How to prevent this ?

When you move from one activity to another, say from activity A to activity B, then the data which you have loaded gets lost. To prevent the data reloading, you need to override onSaveInstanceState(Bundle savedInstance).
#Override
public void onSaveInstanceState(Bundle savedInstanceState) {
super.onSaveInstanceState(savedInstanceState);
// Save UI state changes to the savedInstanceState.
// This bundle will be passed to onCreate if the process is
// killed and restarted.
savedInstanceState.putBoolean("MyBoolean", true);
savedInstanceState.putDouble("myDouble", 1.9);
savedInstanceState.putInt("MyInt", 1);
savedInstanceState.putString("MyString", "Welcome back to Android");
// etc.
}
And you can extract those values by overriding onRestoreInstanceState(Bundle savedInstance).
#Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
// Restore UI state from the savedInstanceState.
// This bundle has also been passed to onCreate.
boolean myBoolean = savedInstanceState.getBoolean("MyBoolean");
double myDouble = savedInstanceState.getDouble("myDouble");
int myInt = savedInstanceState.getInt("MyInt");
String myString = savedInstanceState.getString("MyString");
}
Also you can store and retrieve the arraylist.

After long pause, dynamically added items are not there

I have an Android App, where I have a ListView with a custom adapter and some items are static and some are dynamic (loading them from url).
It works perfect, there's no error, but when I pause my App and play with other apps (like surfing in chrome), then when I return to App, the static items are there, but the dynamic items are gone.
EDIT: I'm using volley StringRequest and Gson to load the items from url.

you have to store your fetched data and you can achieve this in 2 different ways
You can save that data and restore it when you came back to your app using onSaveInstanceState and onRestoreInstanceState methods
#Override
public void onSaveInstanceState(Bundle savedInstanceState) {
super.onSaveInstanceState(savedInstanceState);
// save your date like this
savedInstanceState.putBoolean("MyBoolean", true);
savedInstanceState.putDouble("myDouble", 1.9);
savedInstanceState.putInt("MyInt", 1);
savedInstanceState.putString("MyString", "Welcome back to Android");
// etc.
}
#Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
// Restore your date like this and assign it to your list or where ever you need
// This bundle has also been passed to onCreate.
boolean myBoolean = savedInstanceState.getBoolean("MyBoolean");
double myDouble = savedInstanceState.getDouble("myDouble");
int myInt = savedInstanceState.getInt("MyInt");
String myString = savedInstanceState.getString("MyString");
}
You can store it in your database and restore it back whenever you move to onRestoreSaveInstance
#Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
// fetch data from database and assign it back to your UI
}

Saving the activity to a static variable in order to avoid garbage collection

Will saving the activity to a static variable guarantee that its existing elements will not be garbage collected and that the variables in the activity will still be accessible?

No, Static variables maynot persist forever.
Use SharedPreferences to persist variable values and activity state.
You can also try onSaveInstanceState() and onRestoreInstanceState() methods as explained below.
#Override
public void onSaveInstanceState(Bundle savedInstanceState) {
super.onSaveInstanceState(savedInstanceState);
// Save UI state changes to the savedInstanceState.
// This bundle will be passed to onCreate if the process is
// killed and restarted.
savedInstanceState.putBoolean("MyBoolean", true);
savedInstanceState.putDouble("myDouble", 1.9);
savedInstanceState.putInt("MyInt", 1);
savedInstanceState.putString("MyString", "Welcome back to Android");
}
#Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
// Restore UI state from the savedInstanceState.
// This bundle has also been passed to onCreate.
boolean myBoolean = savedInstanceState.getBoolean("MyBoolean");
double myDouble = savedInstanceState.getDouble("myDouble");
int myInt = savedInstanceState.getInt("MyInt");
String myString = savedInstanceState.getString("MyString");
}
You can read more from here

Android Save Instance State

I have created two activities A and B. In the Activity A, using onSaveInstanceState method I am saving bundle value ex(outState.putString("selectSaveDate", this.CalSelectedDate)) and going to the Activity B. When I hit back button to the Activity A , In the oncreate method the bundle value is null. I am unable to get my saved value in the oncreate method.
#Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.clear();
Log.i("bundleSave", "tester1" + this.CalSelectedDate);
outState.putString("selectSaveDate", this.CalSelectedDate);
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if(savedInstanceState != null){
Log.i("todolist", "dsa" + savedInstanceState.getString("selectSaveDate"));
}
}

You only store data in a bundle in the OnSaveInstanceState method to persist data when your activity is destroyed and re-created (such as when rotating the screen or when the android os may decide to kill your activity if it is low on resources). When you launch activity B on top of your currently executing activity A, A is put in to a stopped state (therefore, your A activity is not destroyed). Also, when you come back from onStop, the next method that is called is onStart() (technically onRestart() is called be before onStart() but I find that callback is rarely ever implemented.
In conclusion, if your trying to keep persist data between launching an activity on top of your currently executing activity, you can just store that data in instance variables for that activity. If your trying to persist data between app launches then your going to want to look into storing data in Android's built in sqllite database or Android's SharedPreferences.
You should also obtain a real good understanding of the Activity lifecycle (its tricky but needed to code successfully in android):
http://developer.android.com/training/basics/activity-lifecycle/index.html

please try to Override onSaveInstanceState(Bundle savedInstanceState) and write the application state values you want to change to the Bundle parameter like this:
#Override
public void onSaveInstanceState(Bundle savedInstanceState) {
super.onSaveInstanceState(savedInstanceState);
// Save UI state changes to the savedInstanceState.
// This bundle will be passed to onCreate if the process is
// killed and restarted.
savedInstanceState.putDouble("myDouble", 1.9);
savedInstanceState.putInt("MyInt", 1);
savedInstanceState.putString("MyString", "How are you");
// etc.
}
it will get passed in to onCreate and also onRestoreInstanceState where you'd extract the values like this:
#Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
// Restore UI state from the savedInstanceState.
// This bundle has also been passed to onCreate.
double myDouble = savedInstanceState.getDouble("myDouble");
int myInt = savedInstanceState.getInt("MyInt");
String myString = savedInstanceState.getString("MyString");
}
or follow activity life cycle for better understanding.

Saving view values while switching between activities in android

I'm working on a tabbed application in android. In the first tab I've a search engine with textviews, spinners.. and if I filled these params and switch to other tab or to the search results activity, and I return back to this tab (search engine tab) I found that all the fields are reinitialized. But I want to keep their value in order to remember what I searched for..
Is there a way to keep my data when I switch between activities ?
Thanks for your help.

You can override onSaveInstanceState (which will be called before you transition to a new activity) and onRestoreInstanceState (which will be called before your activity is resumed) e.g. :
#Override
public void onSaveInstanceState(Bundle savedInstanceState) {
// Save UI state changes to the savedInstanceState.
// This bundle will be passed to onCreate if the process is
// killed and restarted.
savedInstanceState.putBoolean("MyBoolean", true);
savedInstanceState.putDouble("myDouble", 1.9);
savedInstanceState.putInt("MyInt", 1);
savedInstanceState.putString("MyString", "Welcome back to Android");
// etc.
super.onSaveInstanceState(savedInstanceState);
}
#Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
// Restore UI state from the savedInstanceState.
// This bundle has also been passed to onCreate.
boolean myBoolean = savedInstanceState.getBoolean("MyBoolean");
double myDouble = savedInstanceState.getDouble("myDouble");
int myInt = savedInstanceState.getInt("MyInt");
String myString = savedInstanceState.getString("MyString");
}

I guess you are creating intent object to initiate your tab's activity with addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP). Just remove this function if you have done something like this. For example , create intent object like below,
Intent intent = new Intent(this, tabActivity.class);
Not like this,
Intent intent = new Intent(this, tabActivity.class).addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
If you do so , your will get the exact state of a tab as u left it before switching to another tab.