Attempt to invoke virtual method (EditText)

Question

I want my app to take username form user inside the first AlertDialog and publish it on the second AlertDialog, but my app crashes when I add this line of code: txt.setText(edt.getText().toString());. It is supposed to change textview to edittext value which was given on the first AlertDialog. Here are the errors.

java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
    at com.example.myapplication.MainActivity.Alert01(MainActivity.java:73)
    at com.example.myapplication.MainActivity$1.onClick(MainActivity.java:62)
    at android.support.v7.app.AlertController$ButtonHandler.handleMessage(AlertController.java:167)
    at android.os.Handler.dispatchMessage(Handler.java:105)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6541)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)











EditText edt;
TextView txt;

    @Override
    protected void onCreate(Bundle savedInstanceState) {


edt = (EditText) findViewById(R.id.edit_username);
txt = (TextView) findViewById(R.id.text02);


        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        SectionsPagerAdapter sectionsPagerAdapter = new SectionsPagerAdapter(this, getSupportFragmentManager());
        ViewPager viewPager = findViewById(R.id.view_pager);
        viewPager.setAdapter(sectionsPagerAdapter);


        TabLayout tabs = findViewById(R.id.tabs);
        tabs.setupWithViewPager(viewPager);

Alert();
    } 


public void Alert () {

    final AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this, R.style.MyDialogTheme);

    View v = LayoutInflater.from(MainActivity.this).inflate(R.layout.dialog0, null);

    builder.setMessage("Welcome ! ");
    builder.setView(v);


builder.setPositiveButton("Submit", new DialogInterface.OnClickListener() {
    @Override
    public void onClick(DialogInterface dialog, int which) {

        Alert01();
    }
});  

    AlertDialog alert = builder.create();

    alert.show();

}

public void Alert01 (){

    txt.setText(edt.getText().toString());
        AlertDialog.Builder builder01 = new AlertDialog.Builder(MainActivity.this,R.style.MyDialogTheme);
        View v01 = LayoutInflater.from(MainActivity.this).inflate(R.layout.dialog1,null);
    builder01.setView(v01);


        builder01.setTitle("Congratulations ! ");
        AlertDialog alert = builder01.create();
        alert.show();
    }

}

Answer 1

You need to inflate the layout first, then call findViewById in the activity.

EditText edt is a part of AlertDialog1 layout and TextView txt is part of AlertDialog2 layout so you can access edt with reference of AlertDialog1 and txt by reference of AlertDialog2.

Update your code like below :

    EditText edt;
    TextView txt;

        @Override
        protected void onCreate(Bundle savedInstanceState) {

             //  edt = (EditText) findViewById(R.id.edit_username);<--Remove this line from here 
             // txt = (TextView) findViewById(R.id.text02);<--Remoe this line from here and paste both findViewById below to setContentView(R.layout.activity_main) method.

            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);

            SectionsPagerAdapter sectionsPagerAdapter = new SectionsPagerAdapter(this, getSupportFragmentManager());
            ViewPager viewPager = findViewById(R.id.view_pager);
            viewPager.setAdapter(sectionsPagerAdapter);


            TabLayout tabs = findViewById(R.id.tabs);
            tabs.setupWithViewPager(viewPager);

    Alert();
        } 


    public void Alert () {

        final AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this, R.style.MyDialogTheme);

        View v = LayoutInflater.from(MainActivity.this).inflate(R.layout.dialog0, null);

        builder.setMessage("Welcome ! ");
        builder.setView(v);
        edt = (EditText)v.findViewById(R.id.edit_username);

    builder.setPositiveButton("Submit", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {

            Alert01();
        }
    });  

        AlertDialog alert = builder.create();

        alert.show();

    }

    public void Alert01 (){
 // txt.setText(edt.getText().toString());<--Remove this line from here and set it below ...

            AlertDialog.Builder builder01 = new AlertDialog.Builder(MainActivity.this,R.style.MyDialogTheme);
            View v01 = LayoutInflater.from(MainActivity.this).inflate(R.layout.dialog1,null);
        builder01.setView(v01);

        txt = (TextView) v01.findViewById(R.id.text02);
        txt.setText(edt.getText().toString());

            builder01.setTitle("Congratulations ! ");
            AlertDialog alert = builder01.create();
            alert.show();
        }

    }

Answer 2

Move This Line inside Alert() Method after inflating layout

edt = (EditText) v.findViewById(R.id.edit_username);

Also Modify Alert01() Method

    AlertDialog.Builder builder01 = new AlertDialog.Builder(MainActivity.this,R.style.MyDialogTheme);
    View v01 = LayoutInflater.from(MainActivity.this).inflate(R.layout.dialog1,null);
    builder01.setView(v01);
    txt = (TextView) v01.findViewById(R.id.text02);
    txt.setText(edt.getText().toString());