Problems with setOnItemClickListener

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I’m trying to run this Activity as main, but the application even runs on mobile.

The error points to the following lines of code:

FormularioHelper helper = new FormularioHelper(activity);

this.campoNome = activity.findViewById(R.id.nome);

Listaalunosactivity.java

package com.alura.magnero2018.agendaalura;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.Toast;

import java.io.Serializable;
import java.util.List;
import java.util.Objects;
import java.util.concurrent.atomic.AtomicReference;

import alura.modelo.Aluno;
import br.com.alura.dao.AlunoDAO;

public class ListaAlunosActivity extends AppCompatActivity {

    private ListView listaAlunos;
    FormularioActivity activity;
    private FormularioHelper helper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_lista_alunos);
        Button btnNovoAluno = findViewById(R.id.btnNovoAluno);
        listaAlunos = findViewById(R.id.lista_alunos);

        **FormularioHelper helper = new FormularioHelper(activity);**
        Intent intent = getIntent();
        Aluno aluno = ((Aluno) intent.getSerializableExtra("aluno"));
        if (aluno.getNome() !=null) {
            helper.preencheFormulario(aluno);
        }

        listaAlunos.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> lista, View item, int position, long id) {
                Aluno aluno = (Aluno) listaAlunos.getItemAtPosition(position);
                Intent intentVaiProFormulario = new Intent(ListaAlunosActivity.this, FormularioActivity.class);
                intentVaiProFormulario.putExtra("aluno", (Serializable) aluno);
                startActivity(intentVaiProFormulario);
            }
        });

        carregaLista();

        registerForContextMenu(listaAlunos);
        btnNovoAluno.setOnClickListener((v) -> {
            Intent abrirFormulario = new Intent(ListaAlunosActivity.this, FormularioActivity.class);
            startActivity(abrirFormulario);
        });
    }

    private void carregaLista() {
        AlunoDAO dao = new AlunoDAO(this);
        //cria uma lista com os dados buscados do banco
        List<Aluno> alunos = dao.buscaAlunos();
        dao.close();

        /* pega os dados do contexto do layour lista_alunos e transforma-os em ListView */
        ListView listaAlunos = findViewById(R.id.lista_alunos);

        /* transforma os dados do array alunos de string para view */
        ArrayAdapter<Aluno> adapter = new ArrayAdapter<Aluno>(this, android.R.layout.simple_list_item_1, alunos);
        listaAlunos.setAdapter(adapter);
    }

    protected void onResume()
    {
        super.onResume();
    }

    //quando o menu de contexto comecar a ser criado, serao inseridas funcionalidades no menu
    public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo)
    {
        MenuItem deletar = menu.add("Deletar");
        deletar.setOnMenuItemClickListener(new MenuItem.OnMenuItemClickListener() {
           @Override
           public boolean onMenuItemClick(MenuItem item) {
               AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) menuInfo;
               Aluno aluno = (Aluno) listaAlunos.getItemAtPosition(info.position);

               AlunoDAO dao = new AlunoDAO(ListaAlunosActivity.this);
               dao.deleta(aluno);
               dao.close();
               Toast.makeText(ListaAlunosActivity.this, "Aluno " + aluno.getNome() + " deletado com sucesso!", Toast.LENGTH_SHORT).show();
               carregaLista();
               return false;
           }
       });
    }
}

Android Studio returns me the following errors:

Error log

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.alura.magnero2018.agendaalura, PID: 12337
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.alura.magnero2018.agendaalura/com.alura.magnero2018.agendaalura.ListaAlunosActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View com.alura.magnero2018.agendaalura.FormularioActivity.findViewById(int)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3121)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3260)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1976)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6912)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:860)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View com.alura.magnero2018.agendaalura.FormularioActivity.findViewById(int)' on a null object reference
        at com.alura.magnero2018.agendaalura.FormularioHelper.<init>(FormularioHelper.java:64)
        at com.alura.magnero2018.agendaalura.ListaAlunosActivity.onCreate(ListaAlunosActivity.java:37)
        at android.app.Activity.performCreate(Activity.java:7144)
        at android.app.Activity.performCreate(Activity.java:7135)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1293)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3101)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3260) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1976) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:193) 
        at android.app.ActivityThread.main(ActivityThread.java:6912) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:860) 
Application terminated.

activity_list_students.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ListaAlunosActivity"
    android:orientation="vertical">

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

   <Button
       android:id="@+id/btnNovoAluno"
       android:layout_width="56dp"
       android:layout_height="56dp"
       android:text="+"
       android:textColor="#ffffff"
       android:textSize="35sp"
       android:elevation="6dp"
       android:layout_alignParentBottom="true"
       android:layout_alignParentRight="true"
       android:layout_marginBottom="16dp"
       android:layout_marginRight="16dp"
       android:background="@drawable/fundo"
       />

</RelativeLayout>

Forumulariohelper.java

package com.alura.magnero2018.agendaalura;

import android.widget.EditText;
import android.widget.RatingBar;

import com.alura.magnero2018.agendaalura.FormularioActivity;
import com.alura.magnero2018.agendaalura.R;


import alura.modelo.Aluno;

public class FormularioHelper
{
    private EditText campoNome;
    private EditText campoEndereco;
    private EditText campoSitesPessoais;
    private EditText campoTelefone;
    private RatingBar campoNotas;
    private Aluno aluno;

    public EditText getCampoNome() {
        return campoNome;
    }

    public void setCampoNome(EditText campoNome) {
        this.campoNome = campoNome;
    }

    public EditText getCampoEndereco() {
        return campoEndereco;
    }

    public void setCampoEndereco(EditText campoEndereco) {
        this.campoEndereco = campoEndereco;
    }

    public EditText getCampoSitesPessoais() {
        return campoSitesPessoais;
    }

    public void setCampoSitesPessoais(EditText campoSitesPessoais) {
        this.campoSitesPessoais = campoSitesPessoais;
    }

    public EditText getCampoTelefone() {
        return campoTelefone;
    }

    public void setCampoTelefone(EditText campoTelefone) {
        this.campoTelefone = campoTelefone;
    }

    public RatingBar getCampoNotas() {
        return campoNotas;
    }

    public void setCampoNotas(RatingBar campoNotas) {
        this.campoNotas = campoNotas;
    }


    public FormularioHelper(FormularioActivity activity)
    {
        **this.campoNome = activity.findViewById(R.id.nome);**
        this.campoEndereco = activity.findViewById(R.id.endereco);
        this.campoSitesPessoais = activity.findViewById(R.id.sitesPessoais);
        this.campoTelefone = activity.findViewById(R.id.telefone);
        this.campoNotas = (RatingBar) activity.findViewById(R.id.notas);
        Aluno aluno = new Aluno();
    }

    public Aluno pegarAluno()
    {
        Aluno aluno = new Aluno();
        aluno.setNome(String.valueOf(campoNome.getText()));
        aluno.setEndereco(String.valueOf(campoEndereco.getText()));
        aluno.setSite(String.valueOf(campoSitesPessoais.getText()));
        aluno.setTelefone(String.valueOf(campoTelefone.getText()));
        aluno.setNota(Double.valueOf(campoNotas.getProgress()));

        return aluno;
    }

    public void preencheFormulario(Aluno aluno)  {
        campoNome.setText(aluno.getNome());
        campoEndereco.setText(aluno.getEndereco());
        campoTelefone.setText(aluno.getTelefone());
        campoSitesPessoais.setText(aluno.getSite());
        campoNotas.setProgress(aluno.getNota().intValue());
        this.aluno = aluno;
    }
}
android android-activity

2 answers

0

I believe the @Override in this part of the code

 listaAlunos.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override 
        public void onItemCIick(AdapterView<?> lista, View item, int position, long id) {
            Aluno aluno = (Aluno) listaAlunos.getItemAtPosition(position);
            Intent intentVaiProFormulario = new Intent(ListaAlunosActivity.this, FormularioActivity.class);
            intentVaiProFormulario.putExtra("aluno", aluno);
            startActivity(intentVaiProFormulario);
        }
    });

  • I had the same perception, but I don’t know if it would lead to a mistake

  • @Viniciuslino I am searching here to see if I find any reference in relation to this. But from what I have read so far, it can lead to error yes. If you find something, I’ll update the post

  • The problem was the name of the onItemClick method, the l was capitalized. I copied the code from the course I’m doing, and it took me two days to realize that. It is not the first problem I have with the codes of this course, and this is very annoying for those who are learning.

  • Yesterday after I solved these problems there were others, but I can’t edit the post yet because the R class is not being recognized by my Android Studio, and I’m trying to fix this to get to see again the mistakes of yesterday.

  • I edited the post, with the edited code and the new error log.

  • @Lauraregina post xml activity_list students please. You are probably calling some view that is not present in Layout

  • I edited the post and put the xml.

Show 2 more comments

0


The problem was in the part of the code that filled the data on the screen. Because it was in Activity Listaalunosactivity when you should be at Activity Formularioactivity

FormularioHelper helper = new FormularioHelper(this);

        Intent intent = getIntent();
        Aluno aluno = ((Aluno) intent.getSerializableExtra("aluno"));
        if (aluno !=null) {
            helper.preencheFormulario(aluno);
        }

And the position of the element was not being picked up correctly. In this code snippet:

Listaalunosactivity

listaAlunos.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> lista, View item, int position, long id) {
                Aluno aluno = (Aluno) listaAlunos.getItemAtPosition(position);
                Intent intentVaiProFormulario = new Intent(ListaAlunosActivity.this, FormularioActivity.class);
                intentVaiProFormulario.putExtra("aluno", (Serializable) aluno);
                startActivity(intentVaiProFormulario);
            }
        });

==================================================================================

Functional code

Formularioactivity.java

package com.alura.magnero2018.agendaalura;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.Toast;

import alura.modelo.Aluno;
import br.com.alura.dao.AlunoDAO;

public class FormularioActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_formulario);
        FormularioHelper helper = new FormularioHelper(this);

        Intent intent = getIntent();
        Aluno aluno = ((Aluno) intent.getSerializableExtra("aluno"));
        if (aluno !=null) {
            helper.preencheFormulario(aluno);
        }   
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu)
    {
        /*cria um objeto do tipo MenuInflater, o qual é responsável por criar objetos do tipo menu, a partir de um
        arquivo xml
         */
        MenuInflater inflater = getMenuInflater();
        /*metodo que pega a referencia do arquivo xml e pega item por item e vai criando os MenuItem e adicionando no menu */
        inflater.inflate(R.menu.activity_menu_formulario, menu);
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) //switch vai aqui
    {
        FormularioHelper helper = new FormularioHelper(this);

        switch (item.getItemId())
        {
            case R.id.menu_formulario_ok:

                Aluno aluno = helper.pegarAluno();
                AlunoDAO dao = new AlunoDAO(this);
                dao.insere(aluno);
                dao.close();

                Toast.makeText(FormularioActivity.this, "Aluno " + aluno.getNome() + " salvo", Toast.LENGTH_LONG).show();
                Intent abrirLista = new Intent(FormularioActivity.this, ListaAlunosActivity.class);
                startActivity(abrirLista);

                finish();
                break;
        }
        return super.onOptionsItemSelected(item);
    }
}

Java student.

package alura.modelo;

import android.support.annotation.NonNull;
import android.text.Editable;

import java.io.Serializable;

public class Aluno implements Serializable {
    private Long id;
    private String nome;
    private String endereco;
    private String telefone;
    private String site;
    private Double nota;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getNome() {
        return nome;
    }

    public void setNome(String nome) {
        this.nome = nome;
    }

    public String getEndereco() {
        return endereco;
    }

    public void setEndereco(String endereco) {
        this.endereco = endereco;
    }

    public String getTelefone() {
        return telefone;
    }

    public void setTelefone(String telefone) {
        this.telefone = telefone;
    }

    public String getSite() {
        return site;
    }

    public void setSite(String site) {
        this.site = site;
    }

    public Double getNota() {
        return nota;
    }

    public void setNota(Double nota) {
        this.nota = nota;
    }

    @NonNull
    public String toString() {
        return getId() + " " + getNome();
    }
}

Formulariohelper.java

package com.alura.magnero2018.agendaalura;

import android.widget.EditText;
import android.widget.RatingBar;

import com.alura.magnero2018.agendaalura.FormularioActivity;
import com.alura.magnero2018.agendaalura.R;


import alura.modelo.Aluno;

public class FormularioHelper
{
    private EditText campoNome;
    private EditText campoEndereco;
    private EditText campoSitesPessoais;
    private EditText campoTelefone;
    private RatingBar campoNotas;
    private Aluno aluno;

    public EditText getCampoNome() {
        return campoNome;
    }

    public void setCampoNome(EditText campoNome) {
        this.campoNome = campoNome;
    }

    public EditText getCampoEndereco() {
        return campoEndereco;
    }

    public void setCampoEndereco(EditText campoEndereco) {
        this.campoEndereco = campoEndereco;
    }

    public EditText getCampoSitesPessoais() {
        return campoSitesPessoais;
    }

    public void setCampoSitesPessoais(EditText campoSitesPessoais) {
        this.campoSitesPessoais = campoSitesPessoais;
    }

    public EditText getCampoTelefone() {
        return campoTelefone;
    }

    public void setCampoTelefone(EditText campoTelefone) {
        this.campoTelefone = campoTelefone;
    }

    public RatingBar getCampoNotas() {
        return campoNotas;
    }

    public void setCampoNotas(RatingBar campoNotas) {
        this.campoNotas = campoNotas;
    }


    public FormularioHelper(FormularioActivity activity)
    {
        this.campoNome = activity.findViewById(R.id.nome);
        this.campoEndereco = activity.findViewById(R.id.endereco);
        this.campoSitesPessoais = activity.findViewById(R.id.sitesPessoais);
        this.campoTelefone = activity.findViewById(R.id.telefone);
        this.campoNotas = (RatingBar) activity.findViewById(R.id.notas);
        aluno = new Aluno();
    }

    public Aluno pegarAluno()
    {
        Aluno aluno = new Aluno();
        aluno.setNome(String.valueOf(campoNome.getText()));
        aluno.setEndereco(String.valueOf(campoEndereco.getText()));
        aluno.setSite(String.valueOf(campoSitesPessoais.getText()));
        aluno.setTelefone(String.valueOf(campoTelefone.getText()));
        aluno.setNota((double) campoNotas.getProgress());

        return aluno;
    }

    public void preencheFormulario(Aluno aluno)  {
        campoNome.setText(aluno.getNome());
        campoEndereco.setText(aluno.getEndereco());
        campoTelefone.setText(aluno.getTelefone());
        campoSitesPessoais.setText(aluno.getSite());
        campoNotas.setProgress(aluno.getNota().intValue());
        this.aluno = aluno;
    }
}

Listaalunosactivity.java

package com.alura.magnero2018.agendaalura;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.Toast;

import java.io.Serializable;
import java.util.List;
import java.util.Objects;
import java.util.concurrent.atomic.AtomicReference;

import alura.modelo.Aluno;
import br.com.alura.dao.AlunoDAO;

public class ListaAlunosActivity extends AppCompatActivity {

    private ListView listaAlunos;
    FormularioActivity activity;
   private FormularioHelper helper;
    Aluno aluno = new Aluno();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_lista_alunos);
        Button btnNovoAluno = findViewById(R.id.btnNovoAluno);
        listaAlunos = findViewById(R.id.lista_alunos);
        listaAlunos.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> lista, View item, int position, long id) {
                Aluno aluno = (Aluno) listaAlunos.getItemAtPosition(position);
                Intent intentVaiProFormulario = new Intent(ListaAlunosActivity.this, FormularioActivity.class);
                intentVaiProFormulario.putExtra("aluno", (Serializable) aluno);
                startActivity(intentVaiProFormulario);
            }
        });

        carregaLista();

        registerForContextMenu(listaAlunos);
        btnNovoAluno.setOnClickListener((v) -> {
            Intent abrirFormulario = new Intent(ListaAlunosActivity.this, FormularioActivity.class);
            startActivity(abrirFormulario);
        });
    }

    private void carregaLista() {
        AlunoDAO dao = new AlunoDAO(this);
        //cria uma lista com os dados buscados do banco
        List<Aluno> alunos = dao.buscaAlunos();
        dao.close();

        /* pega os dados do contexto do layour lista_alunos e transforma-os em ListView */
        ListView listaAlunos = findViewById(R.id.lista_alunos);

        /* transforma os dados do array alunos de string para view */
        ArrayAdapter<Aluno> adapter = new ArrayAdapter<Aluno>(this, android.R.layout.simple_list_item_1, alunos);
        listaAlunos.setAdapter(adapter);
    }

    protected void onResume()
    {
        super.onResume();
    }

    //quando o menu de contexto comecar a ser criado, serao inseridas funcionalidades no menu
    public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo)
    {
        MenuItem deletar = menu.add("Deletar");
        deletar.setOnMenuItemClickListener(new MenuItem.OnMenuItemClickListener() {
           @Override
           public boolean onMenuItemClick(MenuItem item) {
               AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) menuInfo;
               Aluno aluno = (Aluno) listaAlunos.getItemAtPosition(info.position);

               AlunoDAO dao = new AlunoDAO(ListaAlunosActivity.this);
               dao.deleta(aluno);
               dao.close();
               Toast.makeText(ListaAlunosActivity.this, "Aluno " + aluno.getNome() + " deletado com sucesso!", Toast.LENGTH_SHORT).show();
               carregaLista();
               return false;
           }
       });
    }
}

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