Error calling another screen

Question

I’m trying to call a second screen in Android Studio, but this giving error.

This is the main class:

package br.com.olamundo.parametros;

import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.*;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.*;
import android.content.*;

public class ActMain extends AppCompatActivity implements View.OnClickListener {

    private EditText txtValor;
    private Button btnOk;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.act_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

        txtValor = (EditText)findViewById(R.id.txtValor);
        btnOk = (Button)findViewById(R.id.btnOk);
        btnOk.setOnClickListener(this);
    }
    @Override
    public void onClick(View v) {
        try {
            Intent it = new Intent(ActMain.this, ActSegundaTela.class);
            it.putExtra("VALOR", txtValor.getText().toString());
            startActivity(it);            
        }
        catch(Exception erro)
        {


        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_act_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

When you click the OK button, you get the error:

03-13 17:01:59.931 11712-11712/br.com.olamundo.parametros E/AndroidRuntime: FATAL EXCEPTION: main
Process: br.com.olamundo.parametros, PID: 11712
java.lang.RuntimeException: Unable to start activity ComponentInfo{br.com.olamundo.parametros/br.com.olamundo.parametros.ActSegundaTela}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at br.com.olamundo.parametros.ActSegundaTela.onCreate(ActSegundaTela.java:35)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)

Aluem knows what may be happening?

Answer 1

The problem is happening in the Activity Actsegundatela onCreate method, as described in your stackTrace:

at br.com.olamundo.parametros.ActSegundaTela.onCreate(ActSegundaTela.java:35)

And on this line

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

you can see that the problem is that you are calling the method setOnClickListener on a button that is null for some reason, you may not have called findViewById, or the button is not in xml, or called the findViewById before the setContentView, or the id is wrong... anyway, if you post the Actsegundatela code and the xml layout I can help you solve.

Answer 2

Try to include the following line in your Androidmanifest.xml file:

<activity
android:name="br.com.olamundo.parametros/br.com.olamundo.parametros.ActSegundaTela">
</activity>