Develop Reference

startActivity() doesn't work when app is in background (In this special case)

I'm trying to bring my app from background to foreground. In onHandleIntent() of my custom IntentService class, I have:
Intent intent = new Intent();
intent.setClass(getApplicationContext(), MainActivity.class); // Also tried with "this" instead of getApplicationContext()
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
intent.setAction(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_LAUNCHER);
startActivity(intent);
Now this code works at first sight but I found a scenario where it doesn't work. If you have the app opened and you put it to background via home button and execute startActivity() within ~5 second, there will be a delay before your app will come to foreground. This is a known implementation and you can find the topic discussed on stackoverflow. In this scenario, the app succeeded in coming from background to foreground.
If you repeat the same experiment above, but instead of waiting for the app to come to foreground, go browse (scroll, swipe, etc) around your phone (I was browsing around the google playstore). The result is that startActivity() will get called but the app will not come to the foreground.
I'm not asking for a solution but more of an explanation on why this is happening. Is this intended behavior?

Use the context of your class.
For instance :
Intent intent= new Intent(context, other.class)
Instead of getapplicationContext()

Use the code :
private void startMenuActivity() {
Intent i = new Intent(this, MainActivity.class);
i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP
| Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(i);
finish();
}

the below code works for me,
val login = Intent(applicationContext, SignInActivity::class.java)
login.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK)
login.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
applicationContext.startActivity(login)

Which is the correct way to start an Activity?

Let's say the Activity I want to start is named "OccupyThePieShop"
I was previously using this methodology to start an Activity:
Intent oTPS = new Intent();
timeIntervalConfigIntent.setClassName("com.aXX3AndSpace.KeepInTouch",
"com.aXX3AndSpace.KeepInTouch.OccupyThePieShop");
startActivity(oTPS);
...but was told that this is more the norm:
Intent oTPS = new
Intent(KeepInTouchActivity.this, OccupyThePieShop.class);
KeepInTouchActivity.this.startActivity(oTPS);
...and so I replaced my calls to startActivity() with that usage.
Now, I've come across a couple more ways which seem quite "elegant," namely:
startActivity(new Intent(getApplicationContext(), OccupyThePieShop.class));
...and:
Intent intent = new Intent(this, OccupyThePieShop.class);
startActivity(intent);
Is one way preferred over the others, and if so, why?

I think this is probably an issue of personal preference. I like startActivity(new Intent(this, OccupyThePieShop.class)); because, as you said, it is elegant.

Starting another application from broadcast receiver

I am trying to start an activity from a Receiver after the device boot:
Intent intent = new Intent(Intent.ACTION_MAIN);
intent.setComponent(ComponentName.unflattenFromString("other.apps.package.name/.ActivityName"));
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
intent.addCategory(Intent.CATEGORY_LAUNCHER);
context.startActivity(intent);
This code just works fine when I call it from my activity however it fails when my BroadcastReceiver executes it after bootup. My Logcat shows:
ActivityNotFoundException: Have you declared the activity in your AndroidManifest.xml?
Any pointers will be greatly appreciated. Thanks in advance.

Intent intent = new Intent(context, activity.class);
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
context.startActivity(intent);
i think this 3 lines only needed and the context will be the context u receive in broadcast receiver.

You probably spelled or made a error when you declared your Activity in your manifest. Make sure you put it in there and spelled everything correctly

I think the problem is in the following Line.what is the name of your Activity?is it "ActivityName"?Also Check package name.
intent.setComponent(ComponentName.unflattenFromString("other.apps.package.name/.ActivityName"))

Send application to back & bring to front

I want to develop an application where it will start on particular time & close on particular time. Similar like Alarm but not alarm application.
As per my thinking I will start an service when application first started service will check current time & particular timing to match the condition & when condition is to close application it will simply send application to background so that service will be running & when condition for wake up occurs service will bring application front.
Is this possible? If yes please give an example links or anything helpful.
Also I am trying to understand the service but it's little bit complex for me so if you have link which will help me to understand the service it will be very helpful. Thank You.
Problem Solved:
/*To close the activity/
Intent intent = new Intent(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_HOME);
intent.addCategory(Intent.CATEGORY_DEFAULT);
startActivity(intent);
MainActivity.this.finish();
OR Just finish activity;
MainActivity.this.finish();
/** To start the activity*/
Intent i = new Intent();
i.setAction(Intent.ACTION_MAIN);
i.addCategory(Intent.CATEGORY_LAUNCHER);
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
ComponentName cn = new ComponentName(this, MainActivity.class);
i.setComponent(cn);
startActivity(i);
It worked for me still I if any one have better solution please post below.
Thank You

You can create a BroadcastReceiver to listen for time changes, and at your specified times, create an Intent to launch or to close your main Activity.

Cannot always launch DevicePolicyManager activity from another activity

I have some strange problem. When I try to launch DevicePolicyManager activity from my main activity, it loads properly. However, when I make a notification, call QuestionActivity (if user clicks the notification), and then try to call DevicePolicyManager activity from QuestionActivity, I get (logcat):
INFO/ActivityManager(104): Starting activity: Intent {
act=android.app.action.ADD_DEVICE_ADMIN
cmp=com.android.settings/.DeviceAdminAdd
(has extras) }
WARN/InputManagerService(104): Window already focused, ignoring focus
gain of:
com.android.internal.view.IInputMethodClient$Stub$Proxy#4514a2d0
And nothing appears. This is strange for me, cause I'm able to launch different Android OS activity from QuestionActivity:
//This works
Intent intent = new Intent(Settings.ACTION_BLUETOOTH_SETTINGS);
startActivity(intent);
But I cannot launch the DevicePolicyManager with:
//This works from main activity, but not from QuestionActivity
MyDeviceAdmin admin = new MyDeviceAdmin(this);
Intent intent = new Intent(DevicePolicyManager.ACTION_ADD_DEVICE_ADMIN);
intent.putExtra(DevicePolicyManager.EXTRA_DEVICE_ADMIN,
admin.getDeviceAdminComponent());
intent.putExtra(DevicePolicyManager.EXTRA_ADD_EXPLANATION,
"Additional text explaining why this needs to be added.");
startActivityForResult(intent, 234234234);
I would be very grateful for any help, cause I'm completely stuck.