Develop Reference

Android App opens second instance when "launched" after back button pressed

Short Version:
An application I have been developing opens a second instance when it is "launched" after the back button has been pressed.
Long Version:
When the application is launched from the "home screen" it works fine- if the application is sent to the background by pressing the back arrow button, by pressing the circle button, or the square button to change to a different app - and then the application is resumed through the multi-tasking menu it works perfectly - resuming exactly where it left off - not showing the splash screen again and most importantly not opening a second instance. However if the application is sent to the background and then launched again from the home screen a second instance of the application is created! The splash screen displays again and the main activity is displayed on the screen rather than the last activity that was on the users screen! This is obviously not the desired behavior and many solutions I have attempted do not work.
Manifest:
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:supportsRtl="true"
android:theme="#style/AppTheme"
android:launchMode="singleInstance">
<activity
android:name=".MainActivity"
android:screenOrientation="portrait"
android:launchMode="singleInstance">
</activity>
<activity
android:name=".Settings_area"
android:screenOrientation="portrait" />
<meta-data
android:name="com.google.android.geo.API_KEY"
android:value="AIzaSyDieXTCaFoIL0kJ_IM4UMBSQL3sNn92AWM" />
<activity
android:name=".MapsActivity"
android:label="#string/title_activity_maps" />
<activity android:name=".Splash"
android:launchMode="singleInstance">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".aboutPageActivity" />
<activity android:name=".turnOffFromNotification"
android:noHistory="true"></activity>
</application>
Edit:
I have also attempted to replace launchMode in the application tag with singleTask and singleInstance.

However if the application is sent to the background and then launched again from the home screen a second instance of the application is created! The splash screen displays again and the main activity is displayed on the screen rather than the last activity that was on the users screen!
This is an expected behavior of Android. The back button (its default implementation) is intended for a user to notify the system that he/she is done with the current Activity letting Android to destroy the Activity's instance.
Note, such a behavior has nothing in common with the android:launchMode attribute.
This is obviously not the desired behavior and many solutions I have attempted do not work.
You can't change it. It's a matter of a user who decided to leave the Activity and OS destroying the Activity's instance no more needed.

The situation was resolved by removing android:launchMode="singleInstance"> from everywhere except the <application> tag. Apparently launch mode is best used when the goal is to create another task - which was not the desired behavior. Stock Android masked this behavior while the modified version of Android with Touchwiz did not.

It saves the current Instance...(it will not destroy it).
when you open app again that time it will reopen the same Instance.
import android.view.KeyEvent;
public boolean onKeyDown(int keyCode, KeyEvent event)
{
if (keyCode == KeyEvent.KEYCODE_BACK)
{
moveTaskToBack(true);
return true; // return
}
return false;
}

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'

Android application doesn't appear on recent apps list

i'm deploying an android application (Android 4.0.3) and when I press the home screen the application doesn't stay on the recent apps list. I've noticed that when I restart the application, it starts on the last screen i've navigated before press the home button. Anyone can help? Here is me Manifest:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.test"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk android:minSdkVersion="15" />
<uses-permission android:name="android.permission.INTERNET" />
<application android:icon="#drawable/logo_home"
android:allowBackup="true">
<activity
android:name="com.test.activity.CommunicatorActivity"
android:launchMode="singleTop"
android:label="" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name="com.test.activity.InputActivity"
android:windowSoftInputMode="adjustPan|stateHidden">
</activity>
<activity android:name="com.test.activity.SettingsActivity"
android:windowSoftInputMode="adjustPan|stateHidden">
</activity>
<activity android:name="com.test.activity.OutputActivity"
android:windowSoftInputMode="adjustPan|stateHidden">
</activity>
</application>
</manifest>

I'm going to go out on a limb and suggest that this is your problem:
android:label=""
In your root activity CommunicatorActivity you've set the label to be an empty string. This label is used to identify your app in the list of available apps and because it is empty, this may be causing it not to show up in the list of recent apps.

Remove android:excludeFromRecents="true" from your manifest

You should use
android:label="your app_name"

2 things
Ok, there isn't something obvious in your manifest that should prevent it from appearing in your recents list.
1. Wrong identification
It's not always straight forward to tell which task contains your activity, using the GUI.
One of the possibilities is that an activity from some other app is on top of your task making you believe that your activity isn't there. Since, clearly it resumes to the last screen.
I suggest you to remove the single top temporarily and check the same.
2. Launcher modification
Has the launcher you use the standard launcher? Has the launcher or some other app modified the presentation or behavior of the recents screen (unlikely but worth a check)
For this, I suggest using a stock launcher or try the same app on a different phone or an emulator.
What would help is steps you followed and some screen shots of recents
screen and also of your app

I had the same problem.
The reason is that I had set android:label="" in manifest.xml.
I hadn't set android:launchMode="singleTop".
I declared on purpose android:label="" because I didn't find any better way to remove the title of the action bar from my main activity.
I turned android:label="app_name" again and everything now is OK; the app appears again in recent app list when pressing the home screen and doesn't start on the last navigated screen when restarting it.

Android, how to not destroy the activity when I rotate the device?

I have an app that works only in portrait mode, and I have made the changes in my manifest file for every activity the orientation to be portrait. But when I rotate the device, the activity recreates again.
How to not destroy the activity?

For API 12 and below: add
android:configChanges="orientation"
Add "screenSize" if you are targeting API 13 or above because whenever your orientation changes so does your screen size, otherwise new devices will continue to destroy your activity. See Egg's answer below for more information on using "screenSize"
android:configChanges="orientation|screenSize"
to your Activity in AndroidManifest.xml. This way your Activity wont be restarted automatically. See the documentation for more infos

From the official document flurin said,
Note: If your application targets API level 13 or higher (as declared
by the minSdkVersion and targetSdkVersion attributes), then you should
also declare the "screenSize" configuration, because it also changes
when a device switches between portrait and landscape orientations.
So if your app targets API level 13 or higher, you should set this config instead:
android:configChanges="orientation|screenSize"

The right solution is
android:configChanges="orientation|screenSize"
Android documentation:
The current available screen size has changed. This represents a change in the currently available size, relative to the current aspect ratio, so will change when the user switches between landscape and portrait. However, if your application targets API level 12 or lower, then your activity always handles this configuration change itself (this configuration change does not restart your activity, even when running on an Android 3.2 or higher device).*

I was messing this up for a little bit and then relized that inside the Manifest file I was putting the configChanges on the Application level and not on the Activity Level. Here is what the code looks like when it is correctly working for me.
<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=".MainActivity"
android:configChanges="orientation|screenSize|keyboardHidden">
<intent-filter>
<action android:name="android.intent.action.MAIN"/>
<category android:name="android.intent.category.LAUNCHER"/>
</intent-filter>
</activity>
</application>

Now that Android supports split screen ("multi-window" in Android parlance), you'll probably want to add screenSize|smallestScreenSize|screenLayout|orientation as well. So to handle rotation and split screen you'll want something like this in android:configChanges
<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=".MainActivity"
android:configChanges="orientation|screenSize|keyboardHidden|smallestScreenSize|screenLayout">
<intent-filter>
<action android:name="android.intent.action.MAIN"/>
<category android:name="android.intent.category.LAUNCHER"/>
</intent-filter>
</activity>
</application>

Look at this code in Floating Image. It has the most interesting way of handling screen rotation ever. http://code.google.com/p/floatingimage/source/browse/#svn/trunk/floatingimage/src/dk/nindroid/rss/orientation

write in manifest:
android:configChanges="orientation|screenSize|keyboardHidden"
and override this in activity that solved your problem:
#Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
}

How to have onSearchRequested not open a web browser

I have a button in my app. When it is pressed I call the onSearchRequested() method. When this is called the stock search box comes up so the user can type some junk in there. When they press "Go" I need the results returned back to my application but instead the stock browser is opened and a google search is performed. How can I tell it to return the results to my application instead.
I've tried these items in my manifest.xml file:
<meta-data android:name="android.app.default_searchable"
android:value=".MainActivity" />
<activity android:name=".MainActivity"
android:launchMode="singleTop"
<intent-filter>
<action android:name="android.intent.action.SEARCH" />
</intent-filter>
I've also tried to capture the result in my onCreate with this:
Intent intent = getIntent();
if (Intent.ACTION_SEARCH.equals(intent.getAction()))

This is covered fairly well in the documentation. In particular, you are missing the searchable <meta-data> element (and, presumably, the corresponding XML file). Here is a sample project showing the use of search within an application.