Question

When I launch the application and click the button to go to the Activity, I suddenly get a Force Close. I’ve tried to erase it all and write it again, but it is still there. What could be the problem?

package com.alexgascon.formuladora; 

import android.app.Activity;
import android.view.View.OnClickListener;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;



public class Matematicas extends Activity {

public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);

    final Button BtnEcSegundoGrado = (Button)findViewById(R.id.ecsegundogrado);
    final Button BtnFracciones = (Button)findViewById(R.id.fracciones);
    final Button BtnMCD = (Button)findViewById(R.id.maximocomunBoton);


    BtnMCD.setOnClickListener(new OnClickListener(){

        @Override
        public void onClick(View arg0) {
            Intent MCDintent = new Intent(Matematicas.this,Maximocomun.class);
            startActivity(MCDintent);

        }


    });

}
}

And here is the layout code

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:background="@drawable/pizarramatesverde"
 android:gravity="center" >

<Button
    android:id="@+id/ecsegundogrado"
    android:layout_height="wrap_content"
    android:layout_width="265sp"
    android:text="@string/ecsegundo"
    android:textColor="@color/Negro"
    />
<Button
    android:id="@+id/fracciones"
    android:layout_height="wrap_content"
    android:layout_width="265sp"
    android:text="@string/fracciones"
    android:layout_below="@id/ecsegundogrado"
    android:textColor="@color/Negro"
    />

<Button
    android:id="@+id/maximocomunBoton"
    android:layout_height="wrap_content"
    android:layout_width="265sp"
    android:text="@string/maximocomun"
    android:layout_below="@id/fracciones"
    android:layout_marginBottom="80sp"
    android:textColor="@color/Negro"
    />



</RelativeLayout>

Answer 1

You need to call setContentView before findViewById:

setContentView(R.layout.yourlayoutxmlname);
final Button BtnEcSegundoGrado = (Button)findViewById(R.id.ecsegundogrado);
final Button BtnFracciones = (Button)findViewById(R.id.fracciones);
final Button BtnMCD = (Button)findViewById(R.id.maximocomunBoton);