Android Spinner: Application cannot compile when using setVisibility on spinner

Android Spinner: Application cannot compile when using setVisibility on spinner - android

I've been having issues when trying to setVisibility to a spinner. Basically there are two spinners. The first spinner has the options yes and no. When the program starts the default option will be yes and the second spinner should be invisible. When the user selects no on the first spinner then the second spinner becomes visible. When I comment out the code for visibility the program compiles on the emulator.
I don't know why the app keeps crashing as soon as i try to make the spinner visible or invisible. Any help would be much appreciated. I thank you in advance for your time and effort.
This is my 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:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin" tools:context=".MainActivity">
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal" >
<TextView android:text="#string/CO" android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/co" />
<Spinner
android:id="#+id/attendance"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:entries="#array/Attendance"
android:prompt="#string/present" />
<Spinner
android:id="#+id/status"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:entries="#array/Status"
android:prompt="#string/status" />
</LinearLayout>
This is strings.xml
<resources>
<string name="app_name">Parade State Gen</string>
<string name="CO">CO</string>
<string name="present">Present?</string>
<string name="status">Status</string>
<string name="action_settings">Settings</string>
<string-array name="Attendance">
<item>Yes</item>
<item>No</item>
</string-array>
<string-array name="Status">
<item>LL</item>
<item>OL</item>
<item>PCL</item>
<item>CCL</item>
<item>O/S</item>
<item>CNB</item>
<item>TNB</item>
<item>MC</item>
<item>RSO</item>
<item>RS</item>
<item>OC</item>
<item>AS</item>
<item>AO</item>
</string-array>
This is the main class
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import java.util.ArrayList;
import java.util.List;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.Toast;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
public class MainActivity extends ActionBarActivity {
Spinner attendance, status;
private Button btnSubmit;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
addItemsOnAttendance();
//addListenerOnButton();
}
public void addItemsOnAttendance() {
attendance = (Spinner) findViewById(R.id.attendance);
final ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
this, R.array.Attendance, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
attendance.setAdapter(adapter);
attendance.setOnItemSelectedListener(new OnItemSelectedListener() {
#Override
public void onItemSelected(AdapterView<?> parentView, View selectedItemView, int position, long id) {
String myData = attendance.getSelectedItem().toString();
int pos = adapter.getPosition(myData);
if (pos == 1) {
status.setVisibility(View.INVISIBLE);
//Toast.makeText(getBaseContext(), myData + " already in Spinner", Toast.LENGTH_LONG).show();
// addListenerOnSpinnerItemSelection();
} else {
}
}
#Override
public void onNothingSelected(AdapterView<?> parentView) {
// your code here
}
});
}
public void addListenerOnSpinnerItemSelection () {
status = (Spinner) findViewById(R.id.status);
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
this, R.array.Status, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
status.setAdapter(adapter);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.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();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}

You initialize spinner variable after call setVisiblity, that's why you receiving NullPointerException. It should be something like that:
addListenerOnSpinnerItemSelection();
status.setVisibility(View.INVISIBLE);
Btw, read something about logcat - it impossible to do android apps without it.

Related

How to get the same MenuItem Behaviour in a customView

I want to have an Icon on a custom view (not on the toolbar) that when clicked have the same dropdown list as the menuItem click.
Any thoughts how to do this ?

Create One xml File Inside res->menu say popup.xml or any name what you want
Like below
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item
android:id="#+id/menu1"
android:icon="#android:drawable/ic_menu_search"
android:title="menuItem1"
/>
<item
android:id="#+id/menu2"
android:icon="#android:drawable/ic_menu_search"
android:title="menuItem2"/>
</menu>
then in your activty, on Click of you action bar object call this code below
PopupMenu popup = new PopupMenu(this, view);
popup.getMenuInflater().inflate(R.menu.popup, popup.getMenu());
popup.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
public boolean onMenuItemClick(MenuItem item) {
if (item.getTitle().equals("menuItem1")) {
// handle MenuItem1
} else if (item.getTitle().equals("menuItem2")) {
// handle MenuItem2
}
//......
return true;
}
});
popup.show();

you can try using dropdown spinners. you can use that in any where.
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:padding="10dip"
android:layout_width="fill_parent"
android:layout_height="wrap_content">
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginTop="10dip"
android:text="Category:"
android:layout_marginBottom="5dp"/>
<Spinner
android:id="#+id/spinner"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:prompt="#string/spinner_title"/>
</LinearLayout>
MainActivity.class
package com.example.spinner;
import java.util.ArrayList;
import java.util.List;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.Toast;
import android.widget.AdapterView.OnItemSelectedListener;
class MainActivity extends Activity implements OnItemSelectedListener{
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// Spinner element
Spinner spinner = (Spinner) findViewById(R.id.spinner);
// Spinner click listener
spinner.setOnItemSelectedListener(this);
// Spinner Drop down elements
List<String> categories = new ArrayList<String>();
categories.add("Automobile");
categories.add("Business Services");
categories.add("Computers");
categories.add("Education");
categories.add("Personal");
categories.add("Travel");
// Creating adapter for spinner
ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, categories);
// Drop down layout style - list view with radio button
dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
// attaching data adapter to spinner
spinner.setAdapter(dataAdapter);
}
#Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
// On selecting a spinner item
String item = parent.getItemAtPosition(position).toString();
// Showing selected spinner item
Toast.makeText(parent.getContext(), "Selected: " + item, Toast.LENGTH_LONG).show();
}
public void onNothingSelected(AdapterView<?> arg0) {
// TODO Auto-generated method stub
}
}
If this answer helped you please do not forget to accept :)
Thanks

link adapter to a list view in another activity

I'm working on a posting system in an app.
What I want to do is when I press on the post icon I'll go to another Activity where I have an EditText and a Button.
When I press the button I want to get the text from the EditText and post it in the ListView of the main page or the "feed" page.
I don't seem to know how to link the array adapter to the feed so that the text appears on the ListView.
This is the code:
Main where I need to know what to do:
package com.example.ali.test1;
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.ListView;
import java.util.ArrayList;
public class MainActivity extends ActionBarActivity {
EditText input;
ListView list1;
ArrayAdapter<String> adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.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();
int id2 = item.getItemId();
if (id == R.id.action_settings) {
return true;
} else if (id2 == R.id.action_cart) {
startActivity(new Intent(MainActivity.this, Post.class));
}
return super.onOptionsItemSelected(item);
}
}
This is the post activity :
package com.example.ali.test1;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.ListView;
import java.util.ArrayList;
public class Post extends ActionBarActivity {
ArrayAdapter<String> adapter1;
EditText input;
ListView list;
ArrayAdapter<String> adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_post);
// android:id="#+id/input"
input = (EditText) findViewById(R.id.input);
// android:id="#+id/list"
adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, new ArrayList<String>());
}
// android:onClick="addToList"
public void addToList(View view) {
adapter.add(input.getText().toString());
adapter.notifyDataSetChanged();
// Clear the input
input.setText("");
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_post, 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();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
These are 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:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin"
tools:context="com.example.ali.test1.MainActivity">
<ListView
android:id="#+id/list1"
android:layout_width="match_parent"
android:layout_height="200dp"
android:layout_weight="1" />
</RelativeLayout>
post:
<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:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin"
tools:context="com.example.ali.test1.Post">
<EditText
android:id="#+id/input"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="#id/list" />
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Add to list"
android:onClick="addToList"
android:layout_below="#id/input"/>
</RelativeLayout>
Thank you!

You need to use the method startActivityForResult(new Intent(MainActivity.this, Post.class),1);
in the post activity
public void finish (View v){
String text = input.getText();
Intent intent = new Intent();
intent.putExtra("result",text);
setResult(Activity.RESULT_OK,intent);
finish();
}
and in the main activity you need to define a list for arrayAdapter and add the result to the arrayList
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (requestCode == 1) {
if(resultCode == Activity.RESULT_OK){
String result=data.getStringExtra("result");
list.add(result);
adapter.notifyDataSetChanged();
}
}
}

If the post activity is opened from the main activity - then the sensible way to do this here is to use "startActivityForResult". Your main activity should start your post activity and receive the result in
it's all here in the documentation : http://developer.android.com/training/basics/intents/result.html
You can pass the text value from the post activity back to the main activity in the extras bundle passed to onActivityResult.

Nothing is showing

I'm working on an app where I have the option of "posting", when you press the post button you go to another activity where we have an EditText and a Button, once the Button is pressed the text should be taken and "posted" in the feed page in a ListView.
Now when I press the Button everything is working fine but nothing appears in the listview.
Here's the code:
Post:
package com.example.ali.test1;
import android.app.Activity;
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.text.Editable;
import android.view.View;
import android.widget.EditText;
public class Post extends ActionBarActivity {
EditText input;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_post);
// android:id="#+id/input"
input = (EditText) findViewById(R.id.input);
}
public void addToList(View v) {
Editable text = input.getText();
Intent intent = new Intent();
intent.putExtra("result", text);
setResult(Activity.RESULT_OK, intent);
finish();
}
}
The class where the message should be seen:
package com.example.ali.test1;
import android.app.Activity;
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import java.util.ArrayList;
public class MainActivity extends ActionBarActivity {
ListView list;
ArrayAdapter<String> adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
list= (ListView) findViewById(R.id.list);
adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, new ArrayList<String>());
list.setAdapter(adapter);
}
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (requestCode == 1) {
if (resultCode == Activity.RESULT_OK) {
String result = data.getStringExtra("result");
adapter.add(result);
adapter.notifyDataSetChanged();
}
}
}
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.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();
int id2 = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
else if (id2 == R.id.action_cart) {
startActivityForResult(new Intent(MainActivity.this , Post.class), 1);
}
return super.onOptionsItemSelected(item);
}
}
The xml files:
Post:
<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:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin"
tools:context="com.example.ali.test1.Post">
<EditText
android:id="#+id/input"
android:layout_width="match_parent"
android:layout_height="wrap_content"
/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Add to list"
android:onClick="addToList"
android:layout_below="#id/input"/>
</RelativeLayout>
Main:
<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:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin"
tools:context="com.example.ali.test1.MainActivity">
<ListView
android:id="#+id/list"
android:layout_width="match_parent"
android:layout_height="200dp"
android:layout_weight="1" />
</RelativeLayout>
The problem is that nothing is showing in the listview
any help?

Your not sending your intent.
startActivity(intent);
Then you are not receiving your intent on the other end properly.
You are using the startActivityForResult(); strategy.
In your second activity call the getIntent() method to retrieve your intent and data.

editText.getText() returns null

I have tried searching for answers but i haven't found the fix for my problem yet. I have 2 activities -apple and Bacon. I am trying to learn intents and data passing between activities. The apple activity is supposed to pass the value entered in the EditText field on a button click to the bacon activity which just displays the value.
I am getting the following exception on the stack
Caused by: java.lang.NullPointerException: Attempt to invoke
virtual method 'android.text.Editable android.widget.EditText.getText()'
on a null object reference
The code snippets are as follows:-
apples.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:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin" tools:context=".Apple"
android:background="#009900">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="Apples"
android:id="#+id/applesText"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Go to Bacon"
android:id="#+id/applesButton"
android:layout_below="#+id/applesText"
android:layout_centerHorizontal="true"
android:layout_marginTop="104dp"
android:onClick="onClickApples"/>
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="textPersonName"
android:ems="10"
android:id="#+id/personName"
android:layout_below="#+id/applesText"
android:layout_centerHorizontal="true" />
Apples.java
package com.example.karan.intentexample;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.content.Intent;
import android.widget.EditText;
public class Apple extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_apple);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_apple, 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();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void onClickApples(View view){
final EditText applesInput = (EditText)view.findViewById(R.id.personName);
String userMessage = applesInput.getText().toString();
Intent i = new Intent(this, Bacon.class);
//putExtra takes data in the form of a key-value pair
i.putExtra("appleMessage", userMessage);
startActivity(i);
}
}
Bacon.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:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin"
tools:context="com.example.karan.intentexample.Bacon"
android:background="#72231F">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="Bacon"
android:id="#+id/baconText"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="39dp" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="New Button"
android:id="#+id/baconButton"
android:layout_below="#+id/baconText"
android:layout_centerHorizontal="true"
android:layout_marginTop="99dp" />
Bacon.java
package com.example.karan.intentexample;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
public class Bacon extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_bacon);
Bundle applesData;
applesData = getIntent().getExtras();
//if there is no data in the intent
if(applesData==null)
return;
//get value by using the key in the getString method
String appleMessage = applesData.getString("appleMessage");
final TextView baconText = (TextView)findViewById(R.id.baconText);
baconText.setText(appleMessage);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_bacon, 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();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}

Here:
final EditText applesInput = (EditText)view.findViewById(R.id.personName);
view.findViewById causing issue.change it to:
final EditText applesInput = (EditText)Apple.this.findViewById(R.id.personName);
Because EditText with personName id is in Activity layout instead of inside Button layout(view parameter of onClickApples)

public class Apple extends AppCompatActivity {
private EditText applesInput;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_apple);
applesInput = (EditText)findViewByID(R.id.personName);
}
public void onClickApples(View view){
String userMessage = applesInput.getText().toString();
Intent i = new Intent(this, Bacon.class);
//putExtra takes data in the form of a key-value pair
i.putExtra("appleMessage", userMessage);
startActivity(i);
}
}

App is crashing before opening

I'm working on an app and I've been working on a "post" service where you can write a post and display it on a feed screen made of listview.
Now everything seem to be fine but I don't know why it's crashing before even starting.
Here is the code:
Post class:
package com.example.ali.test1;
import android.app.Activity;
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.text.Editable;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.ListView;
import java.util.ArrayList;
public class Post extends ActionBarActivity {
EditText input;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_post);
// android:id="#+id/input"
input = (EditText) findViewById(R.id.input);
// android:id="#+id/list"
startActivityForResult(new Intent(Post.this , MainActivity.class), 1);
}
public void addToList(View v) {
Editable text = input.getText();
Intent intent = new Intent();
intent.putExtra("result", text);
setResult(Activity.RESULT_OK, intent);
finish();
}
}
in this class I have an edit text and abutton once the button is pressed I'm supposed to get the text in edit text and post in the listView of the other class
Main:
package com.example.ali.test1;
import android.app.Activity;
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import java.util.ArrayList;
public class MainActivity extends ActionBarActivity {
ListView list;
ArrayAdapter<String> adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, new ArrayList<String>());
list.setAdapter(adapter);
}
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (requestCode == 1) if (resultCode == Activity.RESULT_OK) {
String result = data.getStringExtra("result");
adapter.add(result);
adapter.notifyDataSetChanged();
}
}
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.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();
int id2 = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
else if (id2 == R.id.action_cart) {
startActivity(new Intent(MainActivity.this, Post.class));
}
return super.onOptionsItemSelected(item);
}
}
And the xml files are:
Post:
<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:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin"
tools:context="com.example.ali.test1.Post">
<EditText
android:id="#+id/input"
android:layout_width="match_parent"
android:layout_height="wrap_content"
/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Add to list"
android:onClick="addToList"
android:layout_below="#id/input"/>
</RelativeLayout>
Main:
<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:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
android:paddingBottom="#dimen/activity_vertical_margin"
tools:context="com.example.ali.test1.MainActivity">
<ListView
android:id="#+id/list1"
android:layout_width="match_parent"
android:layout_height="200dp"
android:layout_weight="1" />
</RelativeLayout>
any help would be appreciated I've been stuck here for too long.
Thank You.

You are trying to add adapter to a listview which is null, that's why you must be getting NullPointerException. You need to initialize it before you can use it.
You need to add
list= (ListView) findViewById(R.id.mylistview); // replace R.id.mylistview with the id of your listview in layout activity_main
after
setContentView(R.layout.activity_main);
in onCreate method of MainActivity

Change your MainActivity .Because you not initialize Listview properly.
ListView list;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
list= (ListView) findViewById(R.id.list1);
adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, new ArrayList<String>());
list.setAdapter(adapter);
}

First, sorry for my english.
There is problem with android app going to background, where OS release memory for other functions on OS or other application, when it need's memory. There release your object and you have NullPointerException on resume.
How fix this? OnResume event check object value and if it is null, create object.
How test this? Kill process in Android Device Monitor

Develop Reference

The Android operating system is a mobile operating system that was developed by Google (GOOGL?) to be primarily used for touchscreen devices, cell phones, and tablets.

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You initialize spinner variable after call setVisiblity, that's why you receiving NullPointerException. It should be something like that: addListenerOnSpinnerItemSelection(); status.setVisibility(View.INVISIBLE); Btw, read something about logcat - it impossible to do android apps without it.

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