Develop Reference

How can I send a message from one activity to another in real time

I have two activities, when I open Activity2, the Activity1 won't be closed. In Activity1 I have a handle that post a code (handler.postDelayed()), when this code run I need my Activity2 be notified in order to execute a other code too.
My question is: How can I send this message to Activity2 without reopening it.
I tried use an Intent with a specific action and catch it in onNewIntent() in Activity2; it works but the problem is that this reopen my Activity2. And I can't save the data in SharedPrefs cause my postDelayed() have no fix time, then I'd have to be checking all the time.
Does anyone know how I can send this message when my postDelayed() runs and how I catch it in Activity2 without reopening it? Please if possible post a example or a link to one.
Really thanks...

It was a simple solutions, like said #njzk2, was only add
<activity ..
android:launchMode= "singleInstance" />
or
<activity ..
android:launchMode= "singleTask" />
(both works).
Thanks

You shouldn't be using an Activity to handle long-running code, you should probably look into creating an IntentService to handle your background code. The IntentService can broadcast a new Intent when it is finished running the code. Have your first Activity start the Service, then instantiate a BroadcastReceiver in your second Activity to listen for updates from the Service.
Sending an broadcast Intent doesn't start or resume an Activity.
The BroadcastReceiver for an Activity receives and processes
Intent objects even when your app is in the background, but doesn't
force your app to the foreground.

How to recreate recent-apps activity when app is launched from notification

My app and activity is in my list of recent apps when I receive a notification. When I click on the notification, I want the intent of the notification to be honored. In my case I want to restart the activity (brute force) and pass in the new intent: so, finish then re-create. I am reading about such tags as FLAG_ACTIVITY_NEW_TASK and FLAG_ACTIVITY_SINGLE_TOP but I don't understand them enough to know how to force a "finish then re-create` of my activity. And, oh, the activity in question is MainActivity.
The snippet inside GcmListenerService uses
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
for sending the notification intent
Alternatively
If I go with onNewIntent things get complicated because there maybe DialogFragments being displayed, etc. And I would have to clear everything. That is why finish then re-create seem like the simplest solution to me.

Intent flag FLAG_ACTIVITY_CLEAR_TOP should produce the desired behavior. The documentation for Tasks and Back Stack says this in the section for Using Intent Flags:
If the launch mode of the designated activity is "standard", it too is
removed from the stack and a new instance is launched in its place to
handle the incoming intent. That's because a new instance is always
created for a new intent when the launch mode is "standard".
The documentation for FLAG_ACTIVITY_CLEAR_TOP describes the same behavior in more detail.

Create new intent in background

I am looking for a way to launch another app from within my app but so that the focus is not changed from my app to the app launched.
I.e currently I have the new app launched via a intent, however when this is carried out the new app is launched and becomes the app in view, I need it to be kept in the background with my app still in view.
The reason for this?
I am developing an application for internal use that will act like a lock-screen to the device so although things must happen in the background the 'lock-screen' must always be on top.
I have done some research into intents and launching other apps but can not find anything about what I need.
Hope you can help thank you!
Currently the terminal is called like this:
Intent intent = new Intent(Intent.ACTION_MAIN);
intent.setComponent(new ComponentName("jackpal.androidterm", "jackpal.androidterm.RemoteInterface"));
intent.setAction("jackpal.androidterm.RUN_SCRIPT");
intent.putExtra("jackpal.androidterm.iInitialCommand", cmdString);
The reason it needs to be running in the background is so that the app can run commands in terminal without the user having access, but then they 'unlock' the screen they need to then be able to view the terminal and what commands are being run etc

You can not startActivity in Background.Instead start the activity and minimise the activity(in your case this activity is of different application) using moveTaskToBack(true);
In your case, put a condition based on your intent and its params and use moveTaskToBack(true); so that activity will be minimised only when your application launches.

This won't be possible, you will have to start a background Service that does the actual work and only launch the Activity you want to navigate to once your foreground Activity is finished. Depending on your architecture, you can store the Activity to call when your foreground Activity is finished and change it from the service. That way you will have your desire behaviour without having to actually call the Activity.

In addition to the answer from #Meher, in the intent for your current starting activity, you can add the flag FLAG_FROM_BACKGROUND.
With this you get rid of the "blinking" effect (the one where your activity shows for one fraction of second while it discovers wether to go to background)

Multiple Instances of an Activity

I am trying to show the user information on incoming-call screen, whenever there is an incoming-call. So I have a broadcast receiver listening to incoming calls, which starts the intent service, which subsequently starts an activity (with Theme Dialog).
Now, whenever there is an incoming-call, my activity dialog pops up and shows as intended.
Problem: When the activity dialog is already on the screen and incoming-call happens, there is no new activity dialog with new information. I guess that whenever there is an instance, Android does not creates the new one. So it seems like my problem is "creating multiple instances of an activity".
Please note that I am starting an activity from an intent service using FLAG_NEW_TASK.

Google Doc says :
FLAG_ACTIVITY_NEW_TASK
"When using this flag, if a task is already running for the activity
you are now starting, then a new activity will not be started;
instead, the current task will simply be brought to the front of the
screen with the state it was last in."
So, if you want to start a new fresh activity then simply not use this flag only, you should use it with FLAG_ACTIVITY_CLEAR_TASK for the desired result.
For Example:
// Sets the Activity to start in a new, empty task
notifyIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK |
Intent.FLAG_ACTIVITY_CLEAR_TASK);
If the above solution is not what you needed, then have a look at
android:launchMode attribute, declare this attribute with the desired options (i.e. as per your need) in activity tag of manifest file.
Hope this will solve the problem.

Use flag FLAG_ACTIVITY_MULTIPLE_TASK which according to the documentation :
Used in conjunction with FLAG_ACTIVITY_NEW_TASK to disable the behavior of bringing an existing task to the foreground. When set, a new task is always started to host the Activity for the Intent, regardless of whether there is already an existing task running the same thing.
Using this flag along with FLAG_ACTIVITY_NEW_TASK will cause each activity instance to be created as a separate task and thus you can have different dialog pop ups.

Simply add following flags to your Intent .
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK
| Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS
| Intent.FLAG_ACTIVITY_MULTIPLE_TASK);

Starting multiple instances of the same Activity from Service

I want to start multiple instance of the same Activity class from a Service. The reason I'm doing this, is because I have a Service that runs a "scan" daily, and if it finds any malfunctions it should display a popup for each malfunction.
The Activity that I'm starting is more like a Dialog, has a Dialog theme to display info about the malfunction.
Manfiest:
<activity
android:name=".ui.dialogs.MalfunctionActivity"
android:theme="#style/MyDialog"
android:launchMode="standard">
Intent to start the activity from Service:
Intent displayMalf=new Intent(this, MalfunctionActivity.class);
displayMalf.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(displayMalf);
PROBLEM: to start the Activity from a Service I need the FLAG_ACTIVITY_NEW_TASK which somehow cancels the launchMode="standard" from the manifest, and gives me just one Activity even if I try to start multiple diffrent instances.
Is there anyway in which I can achieve this?

It was so simple. There is the flag FLAG_ACTIVITY_MULTIPLE_TASK which according to the documentation :
Used in conjunction with FLAG_ACTIVITY_NEW_TASK to disable the behavior of bringing an existing task to the foreground. When set, a new task is always started to host the Activity for the Intent, regardless of whether there is already an existing task running the same thing.
Was exactly what I need. Thanks and sorry for answering on my question. It is not a habit. :)

Service will take the flag FLAG_ACTIVITY_NEW_TASK to start the activity but here you can try like this:
Set the instance of the handler of the activity of which you want multiple instances, in the service.
When you want the new instance of the activity use handler.sendMessage(msg) and on receiving this msg in your activity, start this activity again.

I guess your app works in the background and will display the popups even if the app is not in the foreground at the moment, right?
Otherwise I would use normal popup's (AlertViews) instead of starting new activities all the time.
If the app works in the background, you could tell the user with the first popup that your app has found one or more malfunctions and that he should activate the app for more details