Francisco, pode colocar o seu codigo principal pra gente?

package caelum.com.br.cadastrocaelum;

import android.app.Activity; import android.content.Intent; import android.os.Bundle; import android.view.Menu; import android.view.MenuItem; import android.view.View; import android.widget.AdapterView; import android.widget.ArrayAdapter; import android.widget.ListView; import android.widget.Toast;

public class ListaAlunosActivity extends Activity {

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

String[] alunos = {"Francisco", "Sales", "Carvalho", "Castro"}; final ListView lista_alunos = (ListView) findViewById(R.id.lista_alunos); final ArrayAdapter adapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, alunos); lista_alunos.setAdapter(adapter);

lista_alunos.setOnItemClickListener(new AdapterView.OnItemClickListener() { @Override public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) { Toast.makeText(ListaAlunosActivity.this, "Posição: " + position, Toast.LENGTH_SHORT).show(); } });

lista_alunos.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() { @Override public boolean onItemLongClick(AdapterView<?> adapterView, View view, int position, long l) { Toast.makeText(ListaAlunosActivity.this, "Aluno: " + lista_alunos.getItemAtPosition(position), Toast.LENGTH_SHORT).show(); return true; } }); }

@Override public boolean onCreateOptionsMenu(Menu menu) { getMenuInflater().inflate(R.menu.menu_lista_alunos, menu); return super.onCreateOptionsMenu(menu); }

@Override public boolean onOptionsItemSelected(MenuItem item) {

switch (item.getItemId()) { case R.id.novo: Intent irParaFormulario = new Intent(this, FormularioActivity.class); startActivity(irParaFormulario); break;

default: break; }

return super.onOptionsItemSelected(item); } }

insira seu código aqui

package caelum.com.br.cadastrocaelum;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

public class ListaAlunosActivity extends Activity {

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

        String[] alunos = {"Francisco", "Sales", "Carvalho", "Castro"};
        final ListView lista_alunos = (ListView) findViewById(R.id.lista_alunos);
        final ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, alunos);
        lista_alunos.setAdapter(adapter);

        lista_alunos.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {
                Toast.makeText(ListaAlunosActivity.this, "Posição: " + position, Toast.LENGTH_SHORT).show();
            }
        });

        lista_alunos.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
            @Override
            public boolean onItemLongClick(AdapterView<?> adapterView, View view, int position, long l) {
                Toast.makeText(ListaAlunosActivity.this, "Aluno: " + lista_alunos.getItemAtPosition(position), Toast.LENGTH_SHORT).show();
                return true;
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_lista_alunos, menu);
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        switch (item.getItemId()) {
            case R.id.novo:
                Intent irParaFormulario = new Intent(this, FormularioActivity.class);
                startActivity(irParaFormulario);
                break;

            default:
                break;
        }

        return super.onOptionsItemSelected(item);
    }
}

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="caelum.com.br.cadastrocaelum">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">

        <activity android:name=".ListaAlunosActivity">

            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>
        <activity android:name=".FormularioActivity" />

    </application>

</manifest>

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:title="Novo"
        android:id="@+id/novo" />

    <item
        android:id="@+id/mapa"
        android:title="Mapa"/>

    <item
        android:id="@+id/enviar_alunos"
        android:title="Enviar Alunos"/>

    <item
        android:id="@+id/receber_alunos"
        android:title="Receber Alunos" />

    <item
        android:id="@+id/preferencias"
        android:title="Preferencias" />

</menu>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ListView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/lista_alunos"/>

</LinearLayout>

Olá Francisco!

Você pode copiar aqui também o conteúdo do arquivo res/values/styles.xml. Talvez o tema da aplicação esteja configurado para não mostrar a barra de menu.