Input and printing from EditText

Question

So I'm trying to get a string from an EditText view and store into a variable which I will then print when the CreateBtn is clicked. Cant quite get this to work. Keeps crashing, I think, because of the CreateBtn and I think it might have something to do with the AlertBox which is where the EditText view is located.

public class MyActivity extends Activity {


// declares vars
final Context context = this;
private Button addClassBtn;
private Button createBtn;
public EditText classNameInput;
private String classTextName;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_my);

    // initializes var
    final LayoutInflater classInfo = getLayoutInflater();
    addClassBtn = (Button) findViewById(R.id.classBtn);
    classNameInput = (EditText) findViewById(R.id.classNameInput);
    createBtn = (Button) findViewById(R.id.createBtn);

    // creates a alert box with a text view when button is clicked
    addClassBtn.setOnClickListener(
        new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            AlertDialog.Builder builder = new AlertDialog.Builder(context);

            builder.setView(classInfo.inflate(R.layout.class_info, null));

            builder.setTitle("Add Class");

            AlertDialog diaBox = builder.create();

            diaBox.show();

        }
    });

    //classNameInput is extracted to a variable
    createBtn.setOnClickListener(
            new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    String className;

                    className = classNameInput.getText().toString();

                    Log.v("EditText", className);

                }
            });

Here is class_info.xml

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content">

<EditText
    android:id="@+id/classNameInput"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginTop="20dp"
    android:layout_marginBottom="20dp"
    android:paddingTop="25dp"
    android:hint="    class name    "
    android:textSize="25sp"
    android:paddingBottom="20dp"
    android:fontFamily="monospace"
    android:inputType="textAutoComplete|textAutoCorrect"
    android:textAlignment="center"
    android:paddingLeft="-10dp"
    android:paddingRight="-10dp" />

<Button
    android:layout_alignParentStart="true"
    android:layout_alignParentLeft="true"
    android:layout_below="@+id/classNameInput"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/createBtn"
    android:fontFamily="monospace"
    android:textSize="23sp"
    android:text="create"
    android:onClick="createBtnClick" />

</RelativeLayout>

Here is activity_my.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=".MyActivity">

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="+"
    android:id="@+id/classBtn"
    android:clickable="false"
    android:textSize="100sp"
    android:layout_centerVertical="true"
    android:layout_centerHorizontal="true"
    android:onClick="onClassBtnClick"
    android:paddingLeft="50dp"
    android:paddingRight="50dp"
    android:paddingTop="10dp"
    android:paddingBottom="10dp"
    android:focusable="true" />

 </RelativeLayout>

Answer 1

I think you got a NullPointerException when you press the createBtn because your classNameInput is null when you trying to use it in the OnClickListener of your createBtn.

The statement "(EditText) findViewById(R.id.classNameInput)" always return null because your EditText is located in the AlterDialog which is not created yet when you use that statement.

In order to solve your problem, I need to know where your createBtn is. It's better if you post your activity_my xml and class_info xml.

Update:

According to layout files you post, I know that you got a NullPointerException immediately when you start your MyActivity because your createBtn is null when you set a OnClickListener to it. The reason is the same as what I said about your classNameInput.

I changed part of you code to solve your problem. The following code should fix your problem:

public class MyActivity extends Activity {


// declares vars
final Context context = this;
private Button addClassBtn;
private Button createBtn;
public EditText classNameInput;
private String classTextName;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_my);
       // initializes var
    final LayoutInflater classInfo = getLayoutInflater();
    addClassBtn = (Button) findViewById(R.id.classBtn);

    // creates a alert box with a text view when button is clicked
    addClassBtn.setOnClickListener(
        new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            AlertDialog.Builder builder = new AlertDialog.Builder(context);

            View dialogView = classInfo.inflate(R.layout.class_info, null);

            setDialogViews(dialogView);

            builder.setView(dialogView);

            builder.setTitle("Add Class");

            AlertDialog diaBox = builder.create();

            diaBox.show();

        }
    });


    private void setDialogViews(View dialogView){
        classNameInput = (EditText) dialogView.findViewById(R.id.classNameInput);
        createBtn = (Button) dialogView.findViewById(R.id.createBtn);

        //classNameInput is extracted to a variable
        createBtn.setOnClickListener(
                new View.OnClickListener() {
                    @Override
                    public void onClick(View view) {
                        String className;

                        className = classNameInput.getText().toString();

                        Log.v("EditText", className);

                    }
                });
    }