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best place to add an action when application starts up or returns to the forground

I need my application to do 2 network calls when ever the app is started for the 1st time, when it has been killed and started again as well as when it has been placed in the background then returned.
I know I can put it in my "MainActivity" onCreate/onResume. I have a class that extends Application which is where I am initialising logging and crash reporting, but I noticed there is no onResume method, which from my understand is the method that is called when the application comes from the background.
Where would be the best place to do these 2 network calls to update certain aspects in my app when the app is started for the 1st time, started when killed and resumed when it comes back from the background.
FYI. The reason I don't want it to go in my "MainActivity" is that I don't want these network calls to be called when ever i return to the MainActivity from another screen in the app, only when the user returns to the app?
Thanks

The use case of calling whenever the app returns from background is by implementing Activity Life Cycle methods in your Application class:
public class myApp extends Application implements Application.ActivityLifecycleCallbacks {
...
}
In this case you make sure that whenever an onPause() is called a corresponding onResume() should also be called (i.e. normal screen switching). If not, then you know that your app is now in background. The next callback to onResume() should mean that it has come to foreground again and you can make your network call.

Distinguish activity calling cases: from other activity/other package/by system

I'm making a simple e-book reader app, and an activity can be called by many cases.
I'd like to distinguish callee activity to know its origin action in case of
From my another activity: this can be easily solved by
StartActivityForResult from calling activity.
Called by back button click from other package app after share action ("whoops, I missed to click share button, and then back.").
Switched by user's multitasking choice.
Called by user click at the start screen: this might be known by MAIN entry point at the android manifest.
How to know above cases?

I have no idea why you would need to do this but...
1.From my another activity: this can be easily solved by StartActivityForResult from calling activity.
Yes, as long as the calling Activity is your own as you can't guarantee any 3rd-party code will use startActivityForResult(...). You can, however, use getCallingPackage() and getCallingActivity() in other cases.
2.Called by back button click from other package app after share action ("whoops, I missed to click share button, and then back.").
When the user presses the BACK button your Activity isn't being "called" - it's simply being resumed or re-started. The original calling app/Activity/method will still hold true - there is no way to ascertain that this has happened as the normal Activity life-cycle methods (onStart() and onResume()) are always called even when an Activity is first created.
3.Switched by user's multitasking choice.
If you mean using the "Recent" apps view, the same applies for my answer to 2. above.
4.Called by user click at the start screen: this might be known by MAIN entry point at the android manifest.
In this case onCreate() will be called although if your Activity is simply stopped for whatever reason, it may simply be restarted depending on the launch mode you use.
In short, I can't see you being able to gather much in the way of any accurate information as to how your Activity becomes active.

I am not too sure about the actual way for the above question as I am too a new guy in android.
But to the best of my knowledge... called by back button and switched by user's multitasking leads the activity to enter pause state.
So you can access it from "onPause" method in your activity.

Activity in Android

As I am new to android, trying to learn the basics in detail. Basically I am an iOS programmer. I would like to know how the "Activity in android" is compared with iOS. That means, what is Activity in android when comparing with iOS.
Thanks in advance.

Check out the Documentation for Activity All of these are in there, and many of them contain more detail than what I've listed here.
1.This hook is called whenever the content view of the screen changes (due to a call to Window.setContentView or Window.addContentView).
2.Called when activity start-up is complete (after onStart() and onRestoreInstanceState(Bundle) have been called).
3.Called when activity resume is complete (after onResume() has been called).
4.This hook is called whenever the window focus changes.
5.Called as part of the activity lifecycle when an activity is about to go into the background as the result of user choice. For example, when the user presses the Home key, onUserLeaveHint() will be called, but when an incoming phone call causes the in-call Activity to be automatically brought to the foreground, onUserLeaveHint() will not be called on the activity being interrupted. In cases when it is invoked, this method is called right before the activity's onPause() callback. This callback and onUserInteraction() are intended to help activities manage status bar notifications intelligently; specifically, for helping activities determine the proper time to cancel a notfication.
6.Called whenever a key, touch, or trackball event is dispatched to the activity.
7.Called when the window has been attached to the window manager.

Although there is no 1:1 match for an Activity in iOS SDK, UIViewController is the closest match.
Beginning Android for iOS Developers can help you to cover some ground in writing your first Android app.

The Activity in Android is like the controller in iOS. It receives UI events, interacts with the data model, and updates the UI.

better to read this :
http://developer.android.com/reference/android/app/Activity.html

Run code when Android app starts and exists

In my app I need to call code whenever the app closes (pauses) and then run code again whenever the app starts again (resumes). For example, I call a web service that syncs the data whenever the app starts or exits. This is easy in iOS because of the central app resume and suspend methods.
I understand the OnPause and OnResume in the Activity, however, is there a central way to handle this? The user could leave the app on Activity3 and come back later, or be in another screen, etc. I'd hate to have to have the same code in every Activity's OnPause and OnResume to handle the "app" startup and shutdown code routines.
Any suggestions?
Thank you.

You could make a common Activity which just handles onResume() and onPause() in a certain way and then make every Activity extend from that one instead of Activity directly.

I would consider subclassing Activty, have each of your activities extend that and just do what you need to when any of them pause or resume.
You could use some static members in an Application class that your new activity base uses to track state or store whatever you need.
Also, Application class has an onCreate() method which will run each time the application is started. There is no pause or resume for Application, however.

Creating a main Activity that is extended by all your other activities and override the onPause and onResume.
But the problem you will face if you want to extend another Activity class such as a ListActivity.
Another approach is to create a new class that extends application and override its onCreate and create a static method that acts as onPause and manually call it by each of your activities

Stopping and starting a Service based on application state

I have a Service which tracks the location of the user. Currently, the Service boots when the application starts and stops when the application terminates. Unfortunately, if users keep the application in the background, the Service never stops and drains battery.
I would like the Service to stop when my application is not in the foreground. I was hoping the Application class would let me Override onPause and onResume handlers, but it does not have them. Is there another way I can accomplish this?

I haven't tested this yet, but it looks like if you use Context#bindService() (instead of Context#startService()), the service should stop when no more activities are bound to it. (see Service lifecycle).
Then use onPause()/onResume() in each activity to bind/unbind from the service.
Alternatively, you could add a pair of methods on your service which tell it to start/stop listening for location updates and call it from each activity's onResume()/onPause(). The service would still be running, but the location updates wouldn't be draining the battery.

Reading all the above answers I would suggest Simply add a boolean global flag for each activity & put it in your onResume & onPause & also while launching an Activity Something like this
public void onPause()
{
super.onPause();
activity1IsResumed = true;
}
&same for onResume
& similarly when launching a new Activity
startActivityForResult(myintent ,0);
activity2IsResumed = true;
activity1IsResumed = false;
then in your Service simply check
if(activity1IsResumed || activity2IsResumed || activity3IsResumed)
{
//your logic
}
else
{
//another logic
//or dont run location tracker
}
& you are done!

You should override the onPause and onResume methods on your Activity. If you have multiple activities you may want to have a common base class for them and put the start/stop logic into the base class.

I have not tried this approach but I think you can override the home key of android device by using KeyEvent.KEYCODE_HOME and you can use stopService(Intent) to stop your service and when again application resumes, you can write startService(Intent) in the onResume() method of your Activity.
This way I think your service will only stop when user explicitly presses home button to take application in the background and not when he switches from one activity to another.

What I would suggest is overriding the onPause/onReume methods as others have said. Without knowing more about the flow of your application and interactions between Activities, I can't give much more information beyond guesswork.
If your Activities are persistent, however, my recommendation would be to utilize the Intents better when switching between Activities.
For instance, each Activity should have a boolean "transition" flag. So, when you move from one Activity to the next, you set up an Intent extra:
intent.putExtra("transition",true);
Followed in the receiving Activity by: (in onCreate)
intent.getBooleanExtra("transition",false);
This way, for each Activity that launches, you can know whether it has come from another Activity, or if it has been launched from a home screen launcher. Thus, if it gets a true transition, then onPause should NOT stop the service--that means you will be returning to the previous Activity after it returns. If it receives no "transition" extra, or a false transition, then you can safely assume there is no Activity underneath it waiting to take over for the current one.
On the first Activity, you will simply need to stop the service if you are switching to another Activity, which you should be able to figure out programmatically if one Activity is started from another.

It sounds like the real problem is how to only stop the service when you go to an activity that isn't one of your own? One way would be to in your onPause method to stop the activity. Do this for all your activities. Then override your startActivity method. And in here do a conditional test to confirm that you are purposefully navigating to one of your own. If your are set a flag to true.
Now go back to your on pause overridden method. And only stop your service if the flag is not equal to true. Set the flag to false.
All events that navigate away will close your service. Navigating to your own will leave it intact.
Do the overriding in a base class that all your activities extend.
Writeen in my andolroid. Will post ezaple later.

Try using the Bound Services technique to accomplish this.
Bound Services | Android Developers
You can use bound services in a way such that the service will stop when no activities are bound to it. This way, when the app is not in the foreground, the service will not be running. When the user brings the app back to the foreground, the Activity will bind to the service and the service will resume.

Create methods registerActivity() and unRegisterActivity() in your Application object and implement first method in all you acts onResume() and second in acts onPause().
First method add activity to List<Activity> instance in your app object, unRegisterActivity() checks size of list in every call if==0 stopService();.