Develop Reference

How to go back from new activity to main navigation drawer activity

First I create app of Navigation Drawer Activity and travel from fragment to new activity, Now I want to set Home Button on New activity which navigates to main activity of navigation drawer.
but when i run it from app it gives me this when Home button is click
but i want to go direct on MainActivity
Here
NewActivity.java
package com.shubham.navi_demo;
import android.content.Intent;
import android.support.v4.app.FragmentActivity;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;
public class NewActivity extends FragmentActivity {
private static Button Button;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_new);
onclickbutton();
}
public void onclickbutton(){
Button = (Button)findViewById(R.id.button);
Button.setOnClickListener(
new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent("android.intent.action.MAIN");
startActivity(intent);
}
}
);
}
}
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<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"
android:label="#string/app_name"
android:theme="#style/AppTheme.NoActionBar">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".NewActivity">
<intent-filter>
<action android:name="com.shubham.navi_demo.NewActivity" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
</manifest>

You don't have to start activity with Intent. Just call finish() in NewActivity, it will show you the Main Navigation drawer activity.
hope this helps.

Intent intent = new Intent(this,MainActivity.class);

Change
Intent intent = new Intent("android.intent.action.MAIN");
to
Intent intent = new Intent(this,MainActivity.class);
or call finish(); to finish() current Activity

Simple solution that you can provide users to navigate back to home screen is explained here.
developer.android.com/training/implementing-navigation/ancestral.html
Add this line to your 'AndroidManifest' under relevant activity declaration.
android:parentActivityName="com.example.your_main_activity"

ActivityNotFoundException: Unable to find explicit activity class {co.edu.unimagdalena.projecto/co.edu.unimagdalena.projecto.informacion2}

i have one package with two class
MainActivity:
package co.edu.unimagdalena.projecto;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
public class MainActivity extends Activity implements OnClickListener {
String[] info;
private EditText nombre;
private EditText apellido;
private EditText email;
private EditText telefono;
private Button enviar;
final static String INFO = "co.edu.unimagdalena.projecto.informacion2";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
nombre=(EditText)findViewById(R.id.EditTextNombre);
apellido=(EditText)findViewById(R.id.EditTextApellidos);
email=(EditText)findViewById(R.id.EditTextCorreo);
telefono=(EditText)findViewById(R.id.EditTextTelefono);
enviar = (Button)findViewById(R.id.BtnEnviar);
enviar.setOnClickListener(this);
info=new String[4];
}
public void onClick (View v){
Intent intent = new Intent (this, informacion2.class);
intent.setClassName("co.edu.unimagdalena.projecto","co.edu.unimagdalena.projecto.informacion2");
startActivity(intent);
}
public void pasarActidadInfo (View v){
info [0] = nombre.getText().toString();
info [1] = apellido.getText().toString();
info [2] = email.getText().toString();
info [3] = telefono.getText().toString();
Intent act = new Intent (this, informacion2.class);
act.putExtra(INFO, info);
startActivity(act);
}
and other class call it informacion2:
package co.edu.unimagdalena.projecto;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.os.Parcel;
import android.os.Parcelable;
import android.widget.TextView;
import co.edu.unimagdalena.projecto.MainActivity;
public class informacion2 extends Activity {
String [] info;
TextView nombre,apellido,email,telefono;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.informacion2);
nombre = (TextView) findViewById(R.id.mostrarNombre);
apellido= (TextView) findViewById(R.id.mostrarApellido);
email = (TextView) findViewById(R.id.mostrarEmail);
telefono = (TextView) findViewById(R.id.mostrarTelefono);
Intent men = getIntent();
info = men.getStringArrayExtra(MainActivity.INFO);
nombre.setText(info[0]);
apellido.setText(info[1]);
email.setText(info[2]);
telefono.setText(info[3]);
}
}
and this is the AndroidManifest.xml file:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="co.edu.unimagdalena.projecto">
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name=".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>
</application>
<activity
android:name=".informacion2"
android:label="#string/app_name">
</activity>
</manifest>
**I already trying everything and the error is not corrected, i am new in android studio
I can fix the error but now android studio give me this error
java.lang.RuntimeException: Unable to start activity ComponentInfo{co.edu.unimagdalena.projecto/co.edu.unimagdalena.projecto.informacion2}: java.lang.NullPointerException: Attempt to read from null array**

Try including other activity inside application in manifest file like this
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name=".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=".informacion2"
android:label="#string/app_name">
</activity>
</application>

setClassName takes a Package Context as first param setClassName(Context packageContext, String className):
In Android manifest
<activity android:name="co.edu.unimagdalena.projecto.informacion2">
And while starting the activity from your main activity
intent.setClassName("co.edu.unimagdalena.projecto","co.edu.unimagdalena.projecto.informacion2");

You are getting NullPointerException inside second activity, when you try to get values of Array. And you are filling array inside pasarActidadInfo method of first activity. The problem is that you are not calling pasarActidadInfo from anywhere after filling array in your first activity. So,your array would be null.
Try calling pasarActidadInfo method when you want to start new activity.
May be in onClick of button.

Always declare all android components (activities, service, receivers) inside the application tag / block and other configurations will be defined outside of application tag/block and inside manifest tag / block in Androidmanifest.xml.
Copy and paste this code in your manifest.xml
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="co.edu.unimagdalena.projecto">
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name=".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=".informacion2"
android:label="#string/app_name">
</activity>
</application>
</manifest>

Android app suddenly stops

I am learning the basics of android programming. Now I have made a Life Cycle test. The list activity works fine, but when I attempt to open the Life Cycle test, the app stops and closes. I have got the same problem on several devices. These are my codes:
(Manifest)
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.badlogic.androidgames"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="21" />
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name=".AndroidBasicsStarter"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.WAKE_LOCK"/>
</manifest>
(AndroidBasicsStarter.java)
package com.badlogic.androidgames;
import android.app.ListActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
public class AndroidBasicsStarter extends ListActivity {
String tests[] = { "LifeCycleTest", "SingleTouchTest", "MultiTouchTest", "KeyTest",
"AccelerometerTest", "AssetsTest", "ExternalStorageTest", "SoundPoolTest",
"MediaPlayerTest", "FullScreenTest", "RenderViewTest", "ShapeTest", "BitmapTest",
"FontTest", "SurfaceViewTest"
};
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setListAdapter(new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, tests));
}
#Override
protected void onListItemClick(ListView list, View view, int position, long id) {
super.onListItemClick(list, view, position, id);
String testName = tests[position];
try {
Class clazz = Class
.forName("com.badlogic.androidgames." + testName);
Intent intent = new Intent(this, clazz);
startActivity(intent);
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
}
(LifeCycleTest.java)
package com.badlogic.androidgames;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;
public class LifeCycleTest extends Activity {
StringBuilder builder = new StringBuilder();
TextView textView;
private void log(String text) {
Log.d("LifeCycleTest", text);
builder.append(text);
builder.append('\n');
textView.setText(builder.toString());
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
textView = new TextView(this);
textView.setText(builder.toString());
setContentView(textView);
log("created");
}
#Override
protected void onResume() {
super.onResume();
log("resumed");
}
#Override
protected void onPause() {
super.onPause();
log("paused");
if (isFinishing()) {
log("finishing");
}
}
}
I use Eclipse on Windows 7. Thank you in advance!

Add your LifeCycleTest activity in AndroidManifest.xml
<activity
android:name=".LifeCycleTest"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
</intent-filter>
</activity>

Include both your activities inside your Manifest file. It should look something like this.
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name=".AndroidBasicsStarter"
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=".LifeCycleTest"
android:label="#string/app_name" >
</activity>
</application>

Program runs with no errors but button wont open

I have been following the mybringback tutorials on youtube and I tried implementing what I learned. Trying to get a button on my main page to open another page. Finally got the program to run without errors but now when I press the button nothing opens.
Main .xml file where my button is
<Button
android:id="#+id/btnChpt3"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="10dp"
android:text="Appearance and Grooming Policies"
android:textSize="18sp"
android:textStyle="bold|italic"
android:gravity="center"
/>
Name of .xml file im trying to get to is chapter3.xml
Menu.java
package com.th3ramr0d.learnar670_1;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class Menu extends Activity{
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button chapterThree = (Button) findViewById(R.id.btnChpt3);
chapterThree.setOnClickListener(new View.OnClickListener() {
// #Override
public void onClick(View v) {
// TODO Auto-generated method stub
startActivity(new Intent("com.th3ramr0d.learnar670_1.CHAPTER3"));
}
});
}
#Override
protected void onPause() {
// TODO Auto-generated method stub
super.onPause();
}
}
And my manifest.
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.th3ramr0d.learnar670_1"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="14"
android:targetSdkVersion="21" />
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name=".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=".Menu"
android:label="#string/app_name" >
<intent-filter>
<action android:name="com.th3ramr0d.learnar670_1.MENU" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name=".Chapter3"
android:label="#string/app_name" >
<intent-filter>
<action android:name="com.th3ramr0d.learnar670_1.CHAPTER3" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
</manifest>
So button ided as btnChpt3 wont open up my .xml file named chapter3.xml. Thanks for the help.
Here is my Chapter3.java
package com.th3ramr0d.learnar670_1;
import android.app.Activity;
import android.os.Bundle;
public class Chapter3 extends Activity{
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.chapter3);
}
}
Here is my MainActivity.java
package com.th3ramr0d.learnar670_1;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
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;
}
#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);
}
}

Copy this and paste in your AndroidManifest and try,
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.th3ramr0d.learnar670_1"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="14"
android:targetSdkVersion="21" />
<application
android:allowBackup="true"
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name=".Menu"
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=".Chapter3"
android:label="#string/app_name" >
<intent-filter>
<action android:name="com.th3ramr0d.learnar670_1.CHAPTER3" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
</manifest>
To help you understand the problem,
<category android:name="android.intent.category.LAUNCHER" />
The code above in the AndroidManifest defines the activity to be launced when the App Icon is pressed. As per your earlier manifest, it launches the activity MainActivity which also sets it setContentView(R.layout.activity_main); by default as the IDE creates a Hello World program.
So when you launch you app, its MainActivity (that looks the same layout you have designed) which is loading and not Menu activity which you want to load. Hence making few changes in the manifest where we declare the Menu activity as the launcher now launches Menu activity which has the piece of code to process your button click.
I hope this helped!

Actually you can try a more convenient way of starting activities inside your application:
startActivity(new Intent(Menu.this, Chapter3.class))
Also you can read more how it works here:
http://developer.android.com/training/basics/firstapp/starting-activity.html

Good day.
Try replacing the line :
startActivity(new Intent("com.th3ramr0d.learnar670_1.CHAPTER3"));
with the code below :
Intent intent = new Intent(Menu.this, Chapter3.class);
startActivity(intent);
Try reverting your code to the original code, copy your layout activity_main.xml and rename it menu.xml.
now in the layout menu.xml change this line:
android:text="Appearance and Grooming Policies"
to:
android:text="Go to menu"
and the line:
android:id="#+id/btnChpt3"
with:
android:id="#+id/btnMenu"
and replace the line:
setContentView(R.layout.activity_main);
in Menu.java with:
setContentView(R.layout.menu.xml);
finally in MainActivity.java add the following to your oncreate method:
Button btnGoToMenu = (Button) findViewById(R.id.btnMenu);
btnGoToMenu.setOnClickListener(new View.OnClickListener() {
// #Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, Menu.class);
startActivity(intent);
}
});
and re-run the application.

Unable to instantiate activity ComponentInfo… java.lang.NullPointerException

OK, so the problem I'm having occurs when the startGame button is pressed. The app crashes when the button is pressed. The activity is instantiated in the manifest so I'm not sure where the error is. The code for the intent is a copy of the other one (which works) so I have no clue where I went wrong.
Error Log:
02-25 14:46:51.064: E/AndroidRuntime(1261): FATAL EXCEPTION: main
02-25 14:46:51.064: E/AndroidRuntime(1261): Process: com.example.hegemony, PID: 1261
02-25 14:46:51.064: E/AndroidRuntime(1261): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.hegemony/com.example.hegemony.PlayerTurn}: java.lang.NullPointerException
Manifest:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.hegemony"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="11"
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.hegemony.SplashScreen"
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.hegemony.StartScreen" >
<intent-filter>
<action android:name="com.example.hegemony.STARTSCREEN" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="com.example.hegemony.SetupHomeScreen" >
<intent-filter>
<action android:name="com.example.hegemony.SETUPHOMESCREEN" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="com.example.hegemony.SetupPlayer"
android:label="#string/app_name" >
<intent-filter>
<action android:name="com.example.hegemony.SETUPPLAYER" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="com.example.hegemony.PlayerTurn"
android:label="#string/app_name" >
<intent-filter>
<action android:name="com.example.hegemony.PLAYERTURN" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
Java Code of sending activity:
public class SetupHomeScreen extends Activity{
private ArrayList<Player> p = GameMaster.players;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_setup_home_screen);
getActionBar().hide();
updatePlayers();
Button gotoInput = (Button) findViewById(R.id.btnSetupPlayer);
gotoInput.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent toInput = new Intent("com.example.hegemony.SETUPPLAYER");
startActivity(toInput);
}
});
Button startGame = (Button) findViewById(R.id.btnStartGame);
startGame.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent toStart = new Intent("com.example.hegemony.PLAYERTURN");
startActivity(toStart);
}
});
}
public void updatePlayers(){
TextView playerList = (TextView) findViewById(R.id.playerList);
String msg = "";
for(int i=0;i < p.size();i++)
msg = msg + "\n - "+p.get(i).getName();
playerList.setText(msg);
if(p.size() >=2){
Button enable = (Button) findViewById(R.id.btnStartGame);
enable.setEnabled(true);
}
}
}
Java code of receiving activity:
public class PlayerTurn extends Activity {
final ActionBar actionBar = getActionBar();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_player_turn);
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
ActionBar.TabListener tabListener = new ActionBar.TabListener() {
#Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
}
#Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
}
#Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
}
};
}
}

Button startGame = (Button) findViewById(R.id.btnStartGame);
startGame.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent toStart = new Intent(SendingActivity.this, NewActivity.class);
startActivity(toStart);
}
});
I think this is how you should start an intent. Maybe its missing a context or the "activityname" is not the right way to do it. I tried to start an activity the way you are trying and it gave me an error as well, not the same one, but it didn't work.
I'm sorry if the solution I'm trying to provide doesn't work. This is really the first time I'm trying to help someone. I hope it works.

As per the logcat error message, your activity class is failing to instantiate. Instantiation involves the allocation and assignment of any class member variables. In the case of PlayerTurn, the only one is this:
final ActionBar actionBar = getActionBar();
The call to getActionBar() throws a NullPointerException because the activity's window has not been built yet - you should call getActionBar() after setContentView() has been called in onCreate(). You can resolve this by simply moving that line of code into onCreate().
If you still want to retain this as a class member variable, declare it but don't assign it:
ActionBar actionBar;
...and then do the assignment in onCreate():
actionBar = getActionBar();