A prompt for user input makes the app crashes - input

Question

I coded a demo for prompt user input, and it always crashes when i click the Ok button on the prompt dialog, giving me this error log:
08-24 06:24:11.669 3275-3275/com.sano.tamer.prompuserinputdialog W/IInputConnectionWrapper: beginBatchEdit on inactive InputConnection
08-24 06:24:11.669 3275-3275/com.sano.tamer.prompuserinputdialog W/IInputConnectionWrapper: endBatchEdit on inactive InputConnection
08-24 06:24:19.019 3275-3275/com.sano.tamer.prompuserinputdialog D/AndroidRuntime: Shutting down VM
08-24 06:24:19.019 3275-3275/com.sano.tamer.prompuserinputdialog W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0x5c8d4160)
08-24 06:24:19.039 3275-3275/com.sano.tamer.prompuserinputdialog E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.sano.tamer.prompuserinputdialog, PID: 3275
java.lang.NullPointerException
at com.sano.tamer.prompuserinputdialog.MainActivity$1$2.onClick(MainActivity.java:48)
at android.support.v7.app.AlertController$ButtonHandler.handleMessage(AlertController.java:157)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:149)
at android.app.ActivityThread.main(ActivityThread.java:5252)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:794)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:610)
at dalvik.system.NativeStart.main(Native Method)
I am using a physical device running KitKat.
Here are the files:
prompts.xml:
<?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"
android:padding="10dp">
<TextView
android:id="#+id/tvUserInput"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/tv_message" />
<EditText
android:id="#+id/etUserInput"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:inputType="text">
<requestFocus/>
</EditText>
</LinearLayout>
activity_main.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
android:orientation="vertical"
tools:context="com.sano.tamer.prompuserinputdialog.MainActivity">
<Button
android:id="#+id/btnShowPrompt"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/button_label"/>
<EditText
android:id="#+id/etResult"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
MainActivity.java:
package com.sano.tamer.prompuserinputdialog;
import android.content.Context;
import android.content.DialogInterface;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
private Button btnShowPrompt;
private EditText etResult;
final Context context = this;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btnShowPrompt = (Button) findViewById(R.id.btnShowPrompt);
etResult = (EditText) findViewById(R.id.etResult);
btnShowPrompt.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
// get prompts.xml view
LayoutInflater inflater = LayoutInflater.from(context);
View vUserPrompt = inflater.inflate(R.layout.prompts,null);
AlertDialog.Builder adBuilder = new AlertDialog.Builder(context);
// set prompts.xml to be the layout file of the alertdialog builder
adBuilder.setView(vUserPrompt);
final EditText etUserInput = (EditText) findViewById(R.id.etUserInput);
// setup a dialog window
adBuilder
.setCancelable(false)
.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialogInterface, int i) {
// get user input and set it to result
etResult.setText(etUserInput.getText());
}
})
.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialogInterface, int i) {
dialogInterface.cancel();
}
});
// create an alert dialog
AlertDialog alertDialog = adBuilder.create();
alertDialog.show();
}
});
}
}