Develop Reference

can not resolve getActivity() and getApplicationContext()

I am learning android from Android Tutorial for Beginners 8 # wrap_content, fill_parent, Password Field and Toast in Android
using android studio 2.2.2.
I have done the same as mentioned in tutorial but unable to understand why getApplicationContext() and getActivity methods are not resolvable.
I have tried getActivity(), getActivity().getApplicationContext(), MainActivity.this.... etc. But Toast.makeText method unable to recognize Context.
Can anyone please tell me what is the exact issue? and how can I resolve it?
Below is my code:
package com.example.programingknowledge.myfirstapp;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
private EditText pass_word;
private Button btn_sbm;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
addListenerOnButton();
}
public void addListenerOnButton() {
pass_word = (EditText) findViewById(R.id.editText);
btn_sbm = (Button) findViewById(R.id.button);
final CharSequence passText = pass_word.getText().toString();
btn_sbm.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Toast.makeText(getApplicationContext(), passText, Toast.LENGTH_SHORT).show();
}
});
}
}
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.programingknowledge.myfirstapp">
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context="com.example.programingknowledge.myfirstapp.MainActivity"
android:background="#android:color/black">
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:inputType="textPassword"
android:ems="10"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:id="#+id/editText" />
<Button
android:text="Button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="23dp"
android:id="#+id/button"
android:layout_below="#+id/editText"
android:layout_centerHorizontal="true" />
</RelativeLayout>

Just change getApplicationContext() or getContext() to YourActivity.this
For example
Toast.makeText(MainActivity.this, passText, Toast.LENGTH_SHORT).show();
Please do not store context as a field. You are able to get in from any point, without storing.

When you are in Activity that means you have the Context i.e. the Activity. You can achieve this by calling this or MainActivity.this. As you are using the Toast inside the OnClickListener object this will not work here because here this means it will take OnClickLister as its object. So here you must use your class.this i.e MainActivity.this.
In case of Fragment you can achieve context by Calling getActivity() because Fragment must have at least a Activity which is the Context.
And the getApplicationContext() means your whole Application Context.
btn_sbm.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Toast.makeText(MainActivity.this, passText, Toast.LENGTH_SHORT).show();
}
});

In your case, you're trying to show a toast from a callback. You should pass the MainActivity.this as context in the makeToast method:
Toast.makeText(MainActivity.this, passText, Toast.LENGTH_SHORT).show();

btn_sbm.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Toast.makeText(getApplicationContext(), passText, Toast.LENGTH_SHORT).show();
}
});
Try this

Please, post your AndroidManifest.xml and activity_main.xml files.
Upd.: The problem is that in your app's build.gradle file was compileSdkVersion 25, but you don't download it. Also you should always download android-sdk sources according to your targetSdkversion. So, just keep your Android Studio files current and that problems should go away.

Toast.makeText(MainActivity.this, passText, Toast.LENGTH_SHORT).show();
The above should work. If not, post your Logcat for the crash.

assign button press to evoke a new page from sliding menu

I've implemented a sliding menu android framework by following a tutorial video, the menu works well but I can't figure out how to make the buttons generate new "fresh", i.e. distinct, pages wherein I can place subsequent components/"activities".
Right now all the buttons do is "toggle" back and forth between having the menu exposed, and hiding the menu, making visible the complete "landing page".
This is how it looks:
In my layout file, I think this is responsible for assigning functionality to the buttons:
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:onClick="toggleMenu"
android:text="Button 1" />
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:onClick="toggleMenu"
android:text="Button 2"/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:onClick="toggleMenu"
android:text="Button 3" />
So as you can see the buttons evoke the method toggleMenu which looks like this:
public void toggleMenu() {
switch (this.menuCurrentState){
case CLOSED:
this.menuCurrentState = MenuState.OPENING;
this.menu.setVisibility(View.VISIBLE);
this.menuAnimatonScroller.startScroll(0, 0, this.getMenuWidth(),
0, menuAnimationDuration);
break;
case OPEN:
this.menuCurrentState = MenuState.CLOSING;
this.menuAnimatonScroller.startScroll(this.currentContentOffset,
0, -this.currentContentOffset, 0, menuAnimationDuration);
break;
default:
return;
}
this.menuAnimationHandler.postDelayed(this.menuAnimationRunnable, menuAnimationPollingInterval);
this.invalidate();
}
I guess I need to make a new method for generating fresh pages and then assign that to the button push rather than toggle menu, I've tried this a few times using intent but I've not been able to quite figure it out.
What do I need to account for in such an operation?
How should such a function look?
The complete code can be found on my github page.
Thank you for your consideration.

dig this tutorial, it's one of the only helpful ones, in my opinion:
http://www.mkyong.com/android/android-activity-from-one-screen-to-another-screen/
or check the pertinent info below"
XML Layouts
Create following two XML layout files in “res/layout/” folder :
res/layout/main.xml – Represent screen 1
res/layout/main2.xml – Represent screen 2
File : res/layout/main.xml
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="I&apos;m screen 1 (main.xml)"
android:textAppearance="?android:attr/textAppearanceLarge" />
<Button
android:id="#+id/button1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Click me to another screen" />
File : res/layout/main2.xml
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="I&apos;m screen 2 (main2.xml)"
android:textAppearance="?android:attr/textAppearanceLarge" />
2. Activities
Create two activity classes :
AppActivity.java –> main.xml
App2Activity.java –> main2.xml
To navigate from one screen to another screen, use following code :
Intent intent = new Intent(context, anotherActivity.class);
startActivity(intent);
File : AppActivity.java
package com.mkyong.android;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.widget.Button;
import android.view.View;
import android.view.View.OnClickListener;
public class AppActivity extends Activity {
Button button;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
addListenerOnButton();
}
public void addListenerOnButton() {
final Context context = this;
button = (Button) findViewById(R.id.button1);
button.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View arg0) {
Intent intent = new Intent(context, App2Activity.class);
startActivity(intent);
}
});
}
}
File : App2Activity.java
package com.mkyong.android;
import android.app.Activity;
import android.os.Bundle;
import android.widget.Button;
public class App2Activity extends Activity {
Button button;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main2);
}
}
3. AndroidManifest.xml
Declares above two activity classes in AndroidManifest.xml.
File : AndroidManifest.xml
<uses-sdk android:minSdkVersion="10" />
<application
android:icon="#drawable/ic_launcher"
android:label="#string/app_name" >
<activity
android:label="#string/app_name"
android:name=".AppActivity" >
<intent-filter >
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:label="#string/app_name"
android:name=".App2Activity" >
</activity>
</application>

<Activity name> cannot be resolved or not a field

I'm trying to perform a simple navigation action using Intent.
I'm using the complete ADT bundle which includes eclipse, SDK and ADT plugins, so no need to configure ADT separately in eclipse.
1.) I started by creating two layouts named activity_main.xml and test2.xml.
2.) Corresponding java files are mainActivity.java and test2.java.
3.) Now activity_main.xml contains a button with id = "click" . Clicking this button should navigate to next activity i.e test2.xml.
4.) The code in mainActivity.java is as below
package com.example.test;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.content.Intent;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.os.Build;
public class MainActivity extends ActionBarActivity
{
Button btn;
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_main);
if (savedInstanceState == null)
{
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}
btn = (Button)findViewById(R.id.click);
//Listening to button event
btn.setOnClickListener(new View.OnClickListener()
{
public void onClick(View arg0) {
//Starting a new Intent
Intent nextScreen = new Intent(getApplicationContext(), test2.class);
startActivity(nextScreen);
}
});
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container,
false);
return rootView;
}
}
}
5.) But when i did so the findViewById(R.id.click) showed error saying "click cannot be resolved or is not a field"
6.) Eclipse suggested me to create a field click in id which i did. It modified the R.java file but it did not help. Though the errors were gone but the emulator threw error saying "the application has stopped"
7.) My manifest.xml file is as below
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.test"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="19" />
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name="com.example.test.MainActivity"
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=".test2"
android:label="#string/app_name" >
<intent-filter>
<action android:name="com.example.test.test2" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
</manifest>
8.) Now my test2.java code is
package com.example.test;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.TextView;
import com.example.test.R;
public class test2 extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.test2);
TextView txtName = (TextView) findViewById(R.id.textView1);
txtName.setText("This is test2 activity");
}
}
Even here at setContentView(R.layout.test2) it shows the similar error as "test2 cannot be resolved or not a field" where as setContentView(R.layout.activity_main) did not show this error
9.) My fragment_main.xml code is as below
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context="com.example.test.MainActivity$PlaceholderFragment" >
<Button
android:id="#+id/click"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:layout_centerInParent="true"
android:layout_marginLeft="14dp"
android:layout_marginTop="65dp"
android:text="#string/button" />
</RelativeLayout>
10.) My test2.xml code is as below
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:id="#+id/textView1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="second page"
android:layout_gravity="center"
/>
</LinearLayout>
The error displayed on running the application is as below
a.) [2014-04-15 18:39:03 - test] W/ResourceType( 8160): ResXMLTree_node header size 0 is too small.
b.) [2014-04-15 18:39:03 - test] C:\Users\KC\Desktop\Android-budle\test\res\menu\main.xml:6: error: Error: No resource found that matches the given name (at 'title' with value '#string/action_settings').
I'm not able to understand what am I missing. Please provide me a solution for this issue, Thanks in advance.

Firstly Check your layout xml. I there is any error then correct it.After that press alt+p then select clean after that it will be build again.

In your activity_main.xml>Button you need to put the android:onClick="methodName". The in your main_activity you schould implement methodName. There you can handle the activities once the Button is clicked.
Another way is to implement the onClickListener to sepertate the XML and the Java files.
Can you add your layout XML files?

Write the onClickListener for your button in your MainActivity onCreate() method and inside it redirect to test2 activity as below:
btn = (Button)findViewById(R.id.click);
btn.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
Intent intent=new Intent(MainActivity.this,test2.class);
startActivity(intent);
}
});
EDITED:
You need to set your view as fragment_main.xml besides activity_main as your Button is inside fragment_main layout.
Just change the
setContentView(R.layout.activity_main);
to
setContentView(R.layout.fragment_main);

There is something wrong syntax wise with your xml files (test2 or activity_main) due to which the auto generated R file will no longer generate the id for the button view.
The main problem seems to be with activity_main as the button contained in it is no longer converted to its corresponding value in R file.
Check those files and if not able to figure out than put the code in order to get help.
Last but not the least check if you have the import statement like import android.R.
You don't need this to be there as it causes such errors if present.
UPDATE:
You are using -
1) setContentView(R.layout.activity_main);
2) btn = (Button)findViewById(R.id.click);
But your layout where you defined your button is setContentView(R.layout.fragment_main);
So btn is trying to find the view in activity_main which is not available.
Solution -
Set the content view to setContentView(R.layout.fragment_main).

How to get the SeekBar work to adjust brightness

First of all, I am new to Android Developing so don't be so harsh on me.
I have tried to get the SeekBar to adjust the brightness level of either the application or the entire system. Although, I have not been able to get this to work.
My XML-file looks like this:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context=".SettingsPage" >
<SeekBar
android:id="#+id/seekBar2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignLeft="#+id/seekBar"
android:layout_below="#+id/seekBar"
android:layout_marginTop="30dp" />
<SeekBar
android:id="#+id/seekBar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="21dp"
android:max="100"
android:progress="50" />
</RelativeLayout>
XML code for MainActivity
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<Button
android:id="#+id/buttonSettings"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:text="Button"
android:onClick="settingsPage"/>
</RelativeLayout>
XML code, the manifest
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.testsetup"
android:versionCode="1"
android:versionName="1.0" >
<uses-permission android:name="android.permission.WRITE_SETTINGS"/>
<uses-sdk
android:minSdkVersion="14"
android:targetSdkVersion="18" />
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name="com.example.testsetup.MainActivity"
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="com.example.testsetup.SettingsPage"
android:label="#string/title_activity_settings_page" >
</activity>
<activity
android:name="com.example.testsetup.BrightnessAdjuster"
android:label="#string/title_activity_brightness_adjuster" >
</activity>
<activity
android:name="com.example.testsetup.BrightnessActivity"
android:label="#string/title_activity_brightness" >
</activity>
</application>
</manifest>
My Java-code that I have looks like this:
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.view.WindowManager;
import android.widget.SeekBar;
import android.widget.SeekBar.OnSeekBarChangeListener;
import android.widget.TextView;
public class SettingsPage extends Activity {
float BackLightValue = 0.5f; // dummy default value
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_settings_page);
SeekBar BackLightControl = (SeekBar) findViewById(R.id.action_settings);
BackLightControl
.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener());
}
public void onClick(View arg0) {
int SysBackLightValue = (int) (BackLightValue * 255);
android.provider.Settings.System.putInt(getContentResolver(),
android.provider.Settings.System.SCREEN_BRIGHTNESS,
SysBackLightValue);
}
public void onProgressChanged(SeekBar arg0, int arg1, boolean arg2) {
BackLightValue = (float) arg1 / 100;
WindowManager.LayoutParams layoutParams = getWindow().getAttributes();
layoutParams.screenBrightness = BackLightValue;
getWindow().setAttributes(layoutParams);
}
public void onStartTrackingTouch(SeekBar arg0) {
}
public void onStopTrackingTouch(SeekBar arg0) {
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.settings_page, menu);
return true;
}
}
Java code for MainActivity
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
public void settingsPage(View view){
Intent intent = new Intent(this, SettingsPage.class);
startActivity(intent);
}
}
The problem is that I do not know if this is the right way, even though I have tried to follow several guides on the matter.
Also, I get one error in the above code, and it is the following line
BackLightControl
.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener());
I get the error that "cannot instantiate type SeekBar.OnSeekBarChangeListener()".
I thought it was due to the fact that OnSeekBarChangeListener was an interface, so I tried to create a random class that implemented OnSeekBarChangeListener and instantiate that class, but that did not work either.
So, now is my question; how to proceed from here?
Regards and thanks in advance
Erik
EDIT
Added my other classes and XML files. Plus, I no longer get the error on the line with instantiating the OnSeekBarChangeListener thing.
Regards
Erik

You cannot in instantiate OnSeekBarChangeListener because it's an interface. If you create a class which implements this interface, and use an instance of that class as the parameter of setOnSeekBarChangeListener, that should definitely work. The easiest way is letting your Activity implement OnSeekBarChangeListener, and pass this to the setter method.
public class SettingsPage extends Activity implements SeekBar.OnSeekBarChangeListener {
// ...
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_settings_page);
SeekBar BackLightControl = (SeekBar) findViewById(R.id.action_settings);
BackLightControl.setOnSeekBarChangeListener(this);
}
#Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
// ...
}
#Override
public void onStartTrackingTouch(SeekBar seekBar) {
// ...
}
#Override
public void onStopTrackingTouch(SeekBar seekBar) {
// ...
}
// ...
}
Side note: you should use standard Java naming conventions, variable names start with lowercase characters.

Android application restarts when opened by clicking the application icon

I am new to the Android development world and I've built a simple "Hello World" app. First, activity requests a text. When the "Go" button is clicked, the app launches the second activity displaying the input text.
If I click the HOME button and then click the application icon, the app launches the first activity again but if I press-hold the home button and click the icon from the "Recent apps" bar, it resumes the app where I left.
How do I avoid this?
I need my app to resume even if the launcher icon is clicked.
MainActivity.java,
package com.example.myfirstandroidapp;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.EditText;
public class MainActivity extends Activity {
public final static String EXTRA_MESSAGE = "com.example.myfirstapp.MESSAGE";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
/** Called when the user clicks the Send button */
public void sendMessage(View view){
// Do something in response to button
Intent intent = new Intent(this, DisplayMessageActivity.class);
EditText editText = (EditText) findViewById(R.id.txtName);
String message = editText.getText().toString();
intent.putExtra(EXTRA_MESSAGE, message);
startActivity(intent);
}
}
DisplayActivity.java,
package com.example.myfirstandroidapp;
import android.annotation.TargetApi;
import android.app.Activity;
import android.content.Intent;
import android.os.Build;
import android.os.Bundle;
import android.support.v4.app.NavUtils;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
public class DisplayMessageActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Get the message from the intent
Intent intent = getIntent();
String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);
// Create the text view
TextView textView = new TextView(this);
textView.setTextSize(40);
textView.setText(message);
// Set the text view as the activity layout
setContentView(textView);
// Show the Up button in the action bar.
setupActionBar();
}
/**
* Set up the {#link android.app.ActionBar}, if the API is available.
*/
#TargetApi(Build.VERSION_CODES.HONEYCOMB)
private void setupActionBar() {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
getActionBar().setDisplayHomeAsUpEnabled(true);
}
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.display_message, menu);
return true;
}
#Override
public void onDestroy(){
super.onDestroy();
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
// This ID represents the Home or Up button. In the case of this
// activity, the Up button is shown. Use NavUtils to allow users
// to navigate up one level in the application structure. For
// more details, see the Navigation pattern on Android Design:
//
// http://developer.android.com/design/patterns/navigation.html#up-vs-back
//
NavUtils.navigateUpFromSameTask(this);
return true;
}
return super.onOptionsItemSelected(item);
}
}
activity_main.xml,
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<EditText
android:id="#+id/txtName"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="70dp"
android:ems="10" >
<requestFocus />
</EditText>
<Button
android:id="#+id/btnGo"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBottom="#+id/txtName"
android:layout_alignParentRight="true"
android:onClick="sendMessage"
android:text="Go!" />
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="#+id/txtName"
android:layout_alignParentTop="true"
android:layout_marginTop="18dp"
android:text="Please input your name:"
android:textAppearance="?android:attr/textAppearanceMedium" />
</RelativeLayout>
activity_display_message.xml,
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context=".DisplayMessageActivity" >
<TextView
android:id="#+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/hello_world" />
</RelativeLayout>
AndroidManifest.xml,
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.myfirstandroidapp"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="9"
android:targetSdkVersion="10" />
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name="com.example.myfirstandroidapp.MainActivity"
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="com.example.myfirstandroidapp.DisplayMessageActivity"
android:label="#string/title_activity_display_message"
android:parentActivityName="com.example.myfirstandroidapp.MainActivity" >
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="com.example.myfirstandroidapp.MainActivity" />
</activity>
</application>
</manifest>

Problem:
I'm not qualified to say this a bug, but there is a behaviour with release builds when starting the application from the launcher. It seems that instead of resuming the previous Activity, it adds a new Activity on top. There is a related bug report on this topic here.
Solution:
I'm working around this this by closing the Launcher Activity if it's not the root of the task, as a result the previous Activity in that task will be resumed.
if (!isTaskRoot()) {
finish();
return;
}

Issue for me was whenever app in installed by an apk with the click on 'Open' option it used to relaunch every time when we minimize it.
resolved it by
SplashActivity.java:
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
if (!isTaskRoot
&& intent.hasCategory(Intent.CATEGORY_LAUNCHER)
&& intent.action != null
&& intent.action.equals(Intent.ACTION_MAIN)) {
finish()
return
}
}