Develop Reference

How do I save the current state of an Android App?

I am new in Android Development. I am trying my hands on developing an alarm app. When I set the alarm, I use a TextView to show the time for which the alarm in set up(initially empty). But when I close or minimize the app and start it again the TextView is again empty. How to get rid of this?
I looked for its solution in android app development manual, but still couldn't find my way out.

Particularly visiting developer.android.com will help you to get started with android development. Anyways you can either use any of the following to save your data:
SharedPreferences
Sqlite Database
File (Pertaining to your app's location)
And when you are reopening your application you can retrieve the information from this methods.

Saving data can be done easily with the SharedPreferences.
private final String SAVED_ALARM_TIME_KEY = "SavedAlarmTime"
private final String ALARM_PREFERENCES = "AlarmPreferences"
private void saveAlarmTime(Context context, long alarmTimestamp) {
SharedPreferences sharedPref = context.getSharedPreferences(ALARM_PREFERENCES, Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPref.edit();
editor.putLong(SAVED_ALARM_TIME, alarmTimestamp);
editor.commit();
}
private long getAlarmTime(Context context) {
SharedPreferences sharedPref = context.getSharedPreferences(ALARM_PREFERENCES, Context.MODE_PRIVATE);
return sharedPref.getLong(SAVED_ALARM_TIME, 0);
}
This is great for something like user settings in the application. But I imagine you will later want to add multiple alarms to your application. In this case it would be better if you used a database. It will provide you with more options to scale the implementation. For instance you wish to add a functionality for repeating alarms at certain days the database will come in very handy.
You can refer to the documentation: https://developer.android.com/reference/android/database/sqlite/SQLiteOpenHelper.html

Android application remember settings

I am coding using Xamarin and have a question about application settings.
Is it possible to have application wide settings? I will give you an example:
I have a map application. I have a ListView where the user can select if the map is using the Street View, Satellite View or default view.
Depending on the item that is selected in the ListView depends of the map view that is shown.
Where and how can I save this selection such that this value is visible throughout the application and when the user exits the application, this setting can be remembered for when the user starts the application up again?
Thanks in advance

Yes, it's possible and also very easy. Usually you save simple application settings using SharedPreferences. They can be read from anywhere in the app.
For writing.
SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(context);
Editor editor = sp.edit();
editor.putBoolean("someBoolean", true);
editor.putString("someString", "string");
editor.commit();
For reading
SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(context);
boolean someBoolean = sp.getBoolean("someBoolean", false);
boolean someString = sp.getString("someString", null);

I suppose you are familiar to Java I/O and android basic concepts. So here I go:
For data persistance in Android, you have two main solutions:
SQLite database
File system
I recommend you to use file system, as you don't really need to organize your data with relational constraints and you will probably not have to make a lot of data persist.
Android documentation is very clear on how to save files:
http://developer.android.com/training/basics/data-storage/files.html
I recommend you to create a Setting class that contains a HashMap attribute:
public class Settings implements Parcelable{
public static HashMap<String,String> settings;
public static void readSettings(){
//Here you read your settings file and you fill your hashmap
}
public static void writeSettings(){
//Here you iterate through your hashmap and you write your setting files
}
}
Every activities will have access to the settings, as the attribute/methods are static. Settings will also be synchronized through every activities (if you change a setting in one activity, every other activities will notice).
If you need some clarifications, leave a comment below.

Saving data between activities using external class

I'm developing an app that has to share strings between activities. I'm trying to get the seperate activities to call a public class with set and get methods. The calling the methods part works and I manage to get a response although the set value has to be rememberd by the set and get class. Here's a link to my set and get class, it's pretty basic: http://pastebin.com/0WabNKz3
Now my question is this: How do I make the set and get class to remember my values between sessions? Feel free ask questions if there's anything you didn't understand.
Thanks!

You need to use SharedPreferences. That's the way to save data even after the app is closed and you can access it from anywhere:
public void savePrefrences(String key, String value)
{
SharedPreferences prefs = context.getSharedPreferences(context.getPackageName(), 0);
prefs.edit().putString(key, value).commit();
}
public String getPrefrences(String key)
{
SharedPreferences prefs = context.getSharedPreferences(context.getPackageName(), 0);
return prefs.getString(key, "");
}
Save the prefrence when and whereever you want and get it whenever and from wherver you want.
The value will not delete when you close the app.

I ended up creating invisible EditTextPreference that now hold the data that I want to keep because they can be shared easily.

When you say saving between sessions, do you mean between the app being paused, or closed completely?
A good resource for lifecycle and storing data across sessions is:
//developer.android.com/training/basics/activity-lifecycle/index.html

How to keep the project always be open using login page on android/eclipse

I have one log in page for the project 'x'.My need is if at first i entered into the project by providing proper values in to the log in page of the project.The project always want to be signed-in, whenever i try to open the project.How to achieve this concept?
Thanks for your precious time!..

Many applications may provide a way to capture user preferences on the settings of a specific application or an activity. For supporting this, Android provides a simple set of APIs.
Preferences are typically name value pairs. They can be stored as “Shared Preferences” across various activities in an application (note currently it cannot be shared across processes). Or it can be something that needs to be stored specific to an activity.
Shared Preferences: The shared preferences can be used by all the components (activities, services etc) off the applications.
Activity handled preferences: These preferences can only be used with in the activity and can not be used by other components of the application.
Shared Preferences:
The shared preferences are managed with the help of the getSharedPreferences method of the Context class. The preferences are stored in a default file(1) or you can specify a file name(2) to be used to refer to the preferences.
(1) Here is how you get the instance when you specify the file name
public static final String PREF_FILE_NAME = "PrefFile";
SharedPreferences preferences = getSharedPreferences(PREF_FILE_NAME, MODE_PRIVATE);
MODE_PRIVATE is the operating mode for the preferences. It is the default mode and means the created file will be accessed by only the calling application. Other two mode supported are MODE_WORLD_READABLE and MODE_WORLD_WRITEABLE. In MODE_WORLD_READABLE other application can read the created file but can not modify it. In case of MODE_WORLD_WRITEABLE other applications also have write permissions for the created file.
(2) The recommended way is to use by the default mode, without specifying the file name:
SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(context);
Finally, once you have the preferences instance, here is how you can retrieve the stored values from the preferences:
int storedPreference = preferences.getInt("storedInt", 0);
To store values in the preference file SharedPreference.Editor object has to be used. Editor is the nested interface of the SharedPreference class.
SharedPreferences.Editor editor = preferences.edit();
editor.putInt("storedInt", storedPreference); // value to store
editor.commit();
Editor also support methods like remove() and clear() to delete the preference value from the file.
Activity Preferences:
The shared preferences can be used by other application components. But if you do not need to share the preferences with other components and want to have activities private preferences. You can do that with the help of getPreferences() method of the activity. The getPreference method uses the getSharedPreferences() method with the name of the activity class for the preference file name.
Following is the code to get preferences:
SharedPreferences preferences = getPreferences(MODE_PRIVATE);
int storedPreference = preferences.getInt("storedInt", 0);
The code to store values is also same as in case of shared preferences.
SharedPreferences preferences = getPreference(MODE_PRIVATE);
SharedPreferences.Editor editor = preferences.edit();
editor.putInt("storedInt", storedPreference); // value to store
editor.commit();
You can also use other methods like storing the activity state in database. Note Android also contains a package called android.preference. The package defines classes to implement application preferences UI.
To see some more examples check Android's Data Storage post on developers site.
For more info, check this link:
Making data persistent in android

Whenever you login set the user inside the preference file. Then in your main activity give a check whether you have value for this preference or not. If present, goto the landing page. Otherwise show the login page.
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
getLandingPage();
}
private void getLandingPage() {
if (isLoggedIn()) {
//goto login page
} else {
//goto landing page
}
}
/**
* Checks whether preference contains any value
*
* #return
*/
private boolean isLoggedIn() {
return ProjectPreferences.getUserName() == ProjectPreferences.NULL_STRING
? true
: false;
}
}
Also don't forget to set username while you login.

How to access a variable present in a service

I want to access a variable present in a service from another service/an activity....
Can anyone give an idea?

To communicate between two service or activity, you need to use AIDL
It is not really difficult to do, and there is a lot of tutorial like this.

You can make a public getter for that variable in your Service class, bind to that service, and access the getter to give you that variable.

If what you mean is that you want to access the variable after you close and open the app, then you're probably looking for SharedPreferences. Note that this requires a context (an activity or service).
To store:
int data = 5;
SharedPreferences storage = getSharedPreferences("storage", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = storage.edit();
editor.putInt("myInt", data);
editor.commit();
To get:
SharedPreferences storage = getSharedPreferences("storage", Context.MODE_PRIVATE);
int data = storage.getInt("myInt", 0);