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Cannot output the contents of an EditText element inside onClick method

I'm relatively new at developing applications in Android Studio or Java and recently ran into a problem I just can't figure out. For now, all I'm trying to achieve is to output the content of the EditText field after a Button is been clicked.
Since I will most likely add more buttons to the Activity later on, I thought that it would be more handy to use a generic onClick where you can separate different button actions inside the switch statement.
Here's a working example in which the onClickListener which does not use a generic onClick method:
package com.example.user.myapp;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
public class MainActivity extends Activity {
private EditText testText;
private Button testButton;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// initialize UI elements
final EditText testText = (EditText) findViewById(R.id.testText);
testButton = (Button) findViewById(R.id.testButton);
// set onClick listener
testButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// it will print the content of testText as long as the "testText" variable is declared as final
System.out.println(testText.getText().toString().trim());
}
});
}
}
Now, if I try to use a generic onClick method, I will suddenly receive a following error:
java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
Here's the code that that causes the error referred above:
package com.example.user.myapp;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
public class MainActivity extends Activity implements View.OnClickListener {
private EditText testText;
private Button testButton;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// initialize the UI elements
EditText testText = (EditText) findViewById(R.id.testText);
Button testButton = (Button) findViewById(R.id.testButton);
// set onClick Listener
testButton.setOnClickListener(this);
}
#Override
public void onClick(View v) {
switch(v.getId()) {
case R.id.testButton:
// this will result in an error
System.out.println(testText.getText().toString().trim());
break;
default:
break;
}
}
Am I missing something here?

on your second code you have defined testText twice
that will work
package com.example.user.myapp;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
public class MainActivity extends Activity implements View.OnClickListener {
private EditText testText;
private Button testButton;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// initialize the UI elements
testText = (EditText) findViewById(R.id.testText);
testButton = (Button) findViewById(R.id.testButton);
// set onClick Listener
testButton.setOnClickListener(this);
}
#Override
public void onClick(View v) {
switch(v.getId()) {
case R.id.testButton:
// this will result in an error
System.out.println(testText.getText().toString().trim());
break;
default:
break;
}
}

Decalre editText globally:
private EditText testText;
Get the view in onCreate():
testText = (EditText) findViewById(R.id.testText);
Use it in the onClick:
System.out.println(testText.getText().toString().trim());

You never initialize the private EditText testText; because you use a local variable instead of referencing the class field in the following call:
final EditText testText = (EditText) findViewById(R.id.testText);
The onClick(View v) is a method of anonymous class implementing the OnClickListener interface and this method references the uninitialized field variable testText.
To fix this, remove the type declaration of a variable before calling findViewById():
this.testText = (EditText) findViewById(R.id.testText)

You have declare EditText 2 time, one is globally and another one is inside the onCreate method, and when you are using Edittext outside the onCreate, you are getting global variable which is not initialize, thats why you are getting this error. use this,
public class MainActivity extends Activity implements View.OnClickListener {
private EditText testText;
private Button testButton;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// initialize the UI elements
testText = (EditText) findViewById(R.id.testText);
testButton = (Button) findViewById(R.id.testButton);
// set onClick Listener
testButton.setOnClickListener(this);
}
#Override
public void onClick(View v) {
switch(v.getId()) {
case R.id.testButton:
// this will result in an error
System.out.println(testText.getText().toString().trim());
break;
default:
break;
}
}

implementing onclicklistener is not working?

I'm trying to implement onclicklistener but it isn't working on my phone or emulator.
here is the code:
package com.slaps.guess;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends Activity implements OnClickListener {
TextView tv;
Button one;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
one = (Button) findViewById(R.id.button1);
tv = (TextView) findViewById(R.id.tvd);
}
public void onClick(View v) {
switch (v.getId()) {
case R.id.button1:
tv.setText("Anything");
break;
}
}
}
the text view is not changing to anything it is still.
note: button1 exists, and their is nothing wrong with my xml.
i want to implement because i have alot of button.

You are missing one.setOnClickListener(this) in your code.
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
one = (Button) findViewById(R.id.button1);
one.setOnClickListener(this);
tv = (TextView) findViewById(R.id.tvd);
}

Before using listener you will have to add it in the object for which you want it.
I guess you want for the Button one here.
Use one.setOnClickListener(this) after one = (Button) findViewById(R.id.button1);

It looks like you're missing the required XML attribute in res/layout/activity_main.xml. Ensure it looks like:
<Button
android:id="#+id/button1"
onClick="onClick"
/>
The key being you have supplied the onClick attribute with the name of your method to invoke.
But if you want to set the click listener programmatically than you will need to use the Button.setOnClickListener method. If you do this your method signature will need to change to:
one.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// Perform action on click
}
});

setOnClickListener Error: No Idea Why?

I am new to Android Development, and I can't for the life of me, figure out why this is giving me an error. The error is occurring on this line: 'bu.setOnClickListener(new OnClickListener() {'
I am following the Android Development Fundamental tutorials on Lynda.com; and my code is identical to that of the teachers; or so I think.
package com.lynda.lyndaproject;
import android.os.Bundle;
import android.app.Activity;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
public class Main extends Activity {
Button bu = (Button) findViewById(R.id.button1);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
bu.setOnClickListener(new OnClickListener() {
public void onClick(View v){
}
});
}
}
By the way, Eclipse doesn't seem to be allowing me to import anything; and I do believe importing 'android.view.View' should have imported everything necessary.

First, you need to fix your import. You are using the wrong OnClickListener. Change the line
import android.content.DialogInterface.OnClickListener;
to
import android.view.View.OnClickListener;
Next, You need to move the line
Button bu = (Button) findViewById(R.id.button1);
To after the call to setContentView(...). So your onCreate method would look like:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button bu = (Button) findViewById(R.id.button1);
bu.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v){
}
});
}
This is because findViewById(...) looks for a View in the current layout. Since this has not been set by setContentView, it will always return null.

need some tips on my code, my code doesn't change text on Android

This code to change text when the user presses a button doesn't work. i tried to change it in some ways but i can't figure out why won't it change... please give me a bit help
package com.cookbook.simple_activity;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class activity extends Activity {
private TextView txt = (TextView) findViewById(R.id.hello_text);
Button startButton = (Button) findViewById(R.id.trigger);
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_simple);
startButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
txt.setText(R.string.pressthisbutton);
}
});
}
}

Change it to
public class activity extends Activity {
private TextView txt;
Button startButton;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_simple);
txt = (TextView) findViewById(R.id.hello_text);
startButton = (Button) findViewById(R.id.trigger);
You need to initialize your Views after inflating your layout with setContentView(). Since your Views exist in your layout, they will return null if you haven't inflated your layout first. You can declare them before your setContentView() but you can't initialize them until after.
Also, since you are trying to access txt inside your listener it must either be final or declared as a member variable as above.
This was a rather easy one to spot but they aren't always. When you post a question try to describe what isn't working and how. Here it would be a NPE I'm guessing when you try to set the listener on your Button so it crashes. When it does crash, please provide the logcat so it is easier for us to spot the problem.

package com.cookbook.simple_activity;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class activity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_simple);
final TextView txt = (TextView) findViewById(R.id.hello_text);
Button startButton = (Button) findViewById(R.id.trigger);
startButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
txt.setText("your text");
}
});
}
}
try this, I moved your button and textview declaring to the body of the activity.

android life cycle always starts with onCreate() method assign the id inside the onCreate
don't use private modifer for the TextView
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class activity extends Activity {
TextView txt;
Button startButton;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_simple);
txt = (TextView) findViewById(R.id.hello_text);
startButton = (Button) findViewById(R.id.trigger);
startButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
txt.setText(R.string.pressthisbutton);
}
});
}
}

Always initialize your textview and other widgets in oncreate method other wise youll get NullPointerException
Try this way
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_simple);
txt = (TextView) findViewById(R.id.hello_text);
startButton = (Button) findViewById(R.id.trigger);
txt.setText("It Working Now!!");

java android handler calling

I am new in the android programming. I see many ways to do the event handling, but when I try to do it by calling the handler class it give error on handling class name:
package com.example.test;
import android.app.Activity;
import android.content.DialogInterface.OnClickListener;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//attach an instance of HandleClick to the Button
findViewById(R.id.button1).setOnClickListener(new HandleClick());
}
private class HandleClick implements OnClickListener{
public void onClick(View arg0) {
Button btn = (Button)arg0; //cast view to a button
// get a reference to the TextView
TextView tv = (TextView) findViewById(R.id.textview1);
// update the TextView text
tv.setText("You pressed " + btn.getText());
}
}
}
"HandleClick" error come on this it say class should be abstract type?
I do not understand why it is giving this error can any one help me?

That's the wrong OnClickListener class. You have
import android.content.DialogInterface.OnClickListener;
You need:
import android.view.View.OnClickListener;
For future reference, the error you get is "The type must implement the inherited abstract method...". This is because you need to implement the DialogInterface's onClick, which should have led you to notice that it was the wrong import (since you have onClick(View))

you imported the wrong OnClickListener, you should import the one from android.view.View

Make it simple & use this,
b1 = (Button) findViewById(R.id.button1);
TextView tv = (TextView) findViewById(R.id.textview1);
b1.setOnClickListener(new OnClickListener()
{
public void onClick(View v)
{
Toast msg = Toast.makeText(getBaseContext(),
"You have clicked Button 1", Toast.LENGTH_LONG);
msg.show();
tv.setText("You pressed " + btn.getText());
}
});