从EditText输入和打印

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);

                    }
                });
    }