Develop Reference

How to run a certain activity in Android Studio?

For instance, I have a few activities within one app, and in order to see a certain activity's UI or whatever, I need to run a certain activity that is not the launcher of the app.
One stupid way is to build a "door" for that activity in the launcher and go inside the activity from the door. However, Is there any better way to run a certain activity alone?

Very easy. Start by exporting the activity you need to run:
Add android:exported="true" in the Activity declaration in the Manifest. This is because am is an external application, and you need to export Activities to allow external application to start them.
Go to "Edit Configurations..." in the "Run" menu.
In the left pane, select your application. In the right pane, in the "General" tab, in the "Launch Options" section, there is a "Launch:" dropdown.
Select "Specified Activity", and enter the name of your activity as it appears in your Manifest.
You can create as many Configurations as you like, and name them according however you like, for example to indicate which activity is being started.

I am using Android Studio stable version 2.1.2 and there is one shortcut to do so. Just open the activity class you wish to run and right click on coding area, There is options to run and debug the particular activity as shown in below screen shot.
For windows use shortcut ctrl+shift+F10 and for mac use ctrl+shift+R. I have tested this in emulator and its working fine, didn't test in actual device.Works only for activity class and don't forget to put cursor in coding area by clicking on it. Also I am not aware whether this option available in older Android studio versions less than 2.1.2.

As mentioned in this answer, you can easily achieve that by giving the activity an action name in the manifest.xml of the app:
<activity android:name="Activity3" ... >
<intent-filter>
<action android:name="com.company.package.FOO"/>
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
then create the following intent from anywhere in order to run this activity specifically:
startActivity(new Intent("com.company.package.FOO"));
After your clarification that the activity has to be run firstly when running the app instead of the launcher, you can achieve that by not setting the content of the launcher activity and instead create an intent that runs the wanted activity:
MainActivity:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//setContentView(R.layout.activity_layout); // remove this line
Intent intent = new Intent(ThisActivity.this, WantedActivity.class);
intent.putExtra("EXIT", false);
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);
}

Add exported true Manifest declaration of that activity.
Go to that activity, right click anywhere, go will get certain option with a 'Run XYZ Activity' option too. just run it

<activity android:name=".phoneVideo">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>

First you need to have two or more activities in your app to start with. Let's say you want to go to a certain activity in your app to display first. May be for testing purposes or any other. Let's see how it can be done,
First you need to find the AndroidManifest.xml file. Its there under the manifests folder.
According to this first dispaly activity is MainActivity
Lets's say I want to make the home activity display first. So what I have to do is simply cut the intent-filter.../intent-filter and paste it within home activity. Like this
First Displaying Acivity is MainActivity according to this,
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:roundIcon="#mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<activity android:name=".home">
</activity>
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
When we want to make the home acivity display first simplay change it as this,
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:roundIcon="#mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<activity android:name=".home">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".MainActivity">
</activity>
</application>
This should work. Hope this will help

For my example, the specific activity was called Activity2 and the project was called ScreenSizes
1- Open the Android Manifest: app>manifests>AndroidManifest.xml
2- Change the activity section for the specific activity to include android:exported="true" like this:
<activity android:name=".Activity2"
android:exported="true">
</activity>
3- Open the java class of the specific activity: app>java>com.example.(your app name)>(specific activity)
in my case it was: app>java>com.example.screensizes>Activity2
4- Right click anywhere in the blank/white area of the Java file and select the option Run '(activity name)'
in my case it was: Run 'Activity2'

Restoring Unity3d Android application with another activity on top

I need the following problem to be resolved:
From the UnityPlayerNativeActivity I am starting a standard Android activity (may be mine, may be with an ad from the ad network - nevermind). When the game is being hidden with this activity on top (not the Unity one) by pressing the home button, as a user I have two ways of restoring it:
from the Recently used apps screen - the app is being restored to the same state, when it was minimized (that is what I expect to happen);
from the launcher, what causes the game's UnityPlayerNativeActivity is being restored with losing all other activities, that have been opened on top of it.
These activities are lost somehow (in a way I don't exactly know, what has happened with them). My game's logic depends on the result of the processes happening there, ie. I need to know, that this particular activity has been exited in any specific way (give a callback for example).
Do you know how I can bring this Unity activity back from launcher with all activities above it, as it was while minimizing it?
I want to understand the difference between the ways of restoring the app from Recently used screen and the launcher. I guess it is related to the intent-filter section within AndroidManifest.xml file, which is included within UnityPlayerNativeActivity entry.

The solution turned out to be quite simple, but not so obvious.
It has turned out, that the AndroidManifest.xml configuration that is being produced by Unity by default is causing this problem. For the main activity that is being started from launcher the following parameters are defined (taken from decompiled app):
<activity
android:alwaysRetainTaskState="true"
android:clearTaskOnLaunch="true"
android:configChanges="locale|fontScale|keyboard|keyboardHidden|mcc|mnc|navigation|orientation|screenLayout|screenSize|smallestScreenSize|touchscreen|uiMode"
android:label="#string/app_name"
android:launchMode="singleTask"
android:name="com.unity3d.player.UnityPlayerNativeActivity"
android:screenOrientation="fullSensor"
launchMode="singleTask">
<meta-data android:name="unityplayer.ForwardNativeEventsToDalvik" android:value="true"/>
<intent-filter>
<action android:name="android.intent.action.MAIN"/>
<category android:name="android.intent.category.LAUNCHER"/>
<category android:name="android.intent.category.LEANBACK_LAUNCHER"/>
</intent-filter>
</activity>
The problematic behaviour is being caused by these 2 parameters:
android:clearTaskOnLaunch="true"
android:launchMode="singleTask"
When the I change them to:
android:clearTaskOnLaunch="false"
android:launchMode="standard"
Then the app is resuming fine from the launcher.
The correct parameters should be set as follows:
<activity
android:alwaysRetainTaskState="true"
android:clearTaskOnLaunch="false"
android:configChanges="locale|fontScale|keyboard|keyboardHidden|mcc|mnc|navigation|orientation|screenLayout|screenSize|smallestScreenSize|touchscreen|uiMode"
android:label="#string/app_name"
android:launchMode="standard"
android:name="com.unity3d.player.UnityPlayerNativeActivity"
android:screenOrientation="fullSensor"
launchMode="standard">
<meta-data android:name="unityplayer.ForwardNativeEventsToDalvik" android:value="true"/>
<intent-filter>
<action android:name="android.intent.action.MAIN"/>
<category android:name="android.intent.category.LAUNCHER"/>
<category android:name="android.intent.category.LEANBACK_LAUNCHER"/>
</intent-filter>
</activity>
Note: While I am able to set the value android:clearTaskOnLaunch="false" for this activity explicitly, the launchMode parameter will be forced by Unity3d and set to "singleTask". I managed to change and check it by decompiling the app and rebuilding from these changed resources. I wonder if there is any elegant way to set this value.

You may find this blog post useful:
http://inthecheesefactory.com/blog/understand-android-activity-launchmode/en

Android - Launcher Activity showing for one second

so, I have a little problem, while opening my app.
I have an "ugly" popup opening for 1-2 sec and then my app goes in.
How exactly can I open my app directly without that 2 sec empty page?
btw - I changed the string of the android:name of my launcher activity to verify that it is this exact activity that is opening empty, and the name changed in the actionbar so it is this activity.
the picture of the first and "ugly" screen
<---
here's my manifest code :
<application
android:name=".BaseApplication"
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#android:style/Theme.Holo.Light.NoActionBar" >
<activity
android:name=".UI.activity.HomeActivity"
android:label="#string/app_name"
android:screenOrientation="portrait"
android:windowSoftInputMode="adjustResize"
android:launchMode='singleTask'
android:theme="#style/Theme.MyAppTheme">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
anyone had this kind of problem before?
thanks a lot.

if anyone ever experience this kind of issue like me,
the solution for me was changing the theme of the app to
android:theme="#android:style/Theme.Holo.Light.NoActionBar"
thank you Kesh for relating that question!

android application not closing

I am in trouble, I want to start my application from starting every time but it's not being.
When I exit from my application & come again. I found same activity which I have left before exit.
Now If I **shut down or switch off** my Android Device direct when my application is in foreground & then I **switch on device again**. I get same activity which I have left earlier. But I want to fresh application from login page. Because my setter & getter is null after switch on device, and I found all value null in my application.
My Manifest file is below:
<activity
android:name=".Main"
android:launchMode="singleTop"
android:screenOrientation="portrait"
android:theme="#android:style/Theme.Dialog" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".screens.ScreenSplash"
android:screenOrientation="portrait" />
<activity android:name=".screens.LoginActivity" />
<activity
android:name=".screens.LoginActivity"
android:configChanges="orientation|keyboardHidden" />
<activity
android:name=".screens.MainMenu"
android:configChanges="orientation|keyboardHidden" />
Kindly help me which is the problem & what should I do. Any help would be appreciated.

Add to your activity manifest
android:clearTaskOnLaunch="true"

According to your Manifest .Main is the launcher activity. so when your application is launched from icon tap then this is the first activity to display and rather if your application is not having any other activity on top of the stack.
so if you want to see the fresh login activity then make the login activity as launcher activity.

Maybe you want to try setting launchMode to standard?
http://developer.android.com/guide/topics/manifest/activity-element.html

How to avoid force close on mobile phone orientation change?

my android application crashes and shows force close when i tilt the mobile phone. is there any suggestions that i can remove such problem? By the way i am developing a LBS application which uses the google maps (MapView).
I have a splash screen and then shown a ListActivity as below :
<activity android:name=".Splash" android:label="#string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".Home" android:label="#string/app_name" android:configChanges="orientation" android:windowSoftInputMode="stateHidden">
<intent-filter>
<action android:name="com.nepways.HOME" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
what is wrong with my declaration, the splash screen loads and list activity is also whown correctly but when i change the orientation the application is closed. Please help me.

When you change your orientation the activity is restarted
look at the logcat to see what exception causes your application to FC
You can change your manifest to disable activity restarting by customizing configChanges, if you stil have the problem override onConfigurationChanged() to fix what is generating this exception (like initialize something that may cause a nullpointer)

First of all as it is said the app is restarting (or as it is said in reference redrawing) each time when you change orientation.
To block it in your manifest file in activity you have to put this line which describes the activity orientation:
<activity android:name=".Splash"
android:label="#string/app_name"
android:screenOrientation="portrait">...
And about this buttons, or keymaps. Telling the truth Ive got thise warnings sometimes but it doesnt change anything in my app. So first change the orientation settings and then it should work correct.
If you want use other screen orientation remember to check here:
http://developer.android.com/guide/topics/manifest/activity-element.html

If you want to avoid restarting your activity on orientation change, you can put this in the activity in the manifest file:
android:configChanges="orientation"
Otherwise, we will need to see more code, and a stacktrace.