如何在ArrayList和ArrayAdpter中添加项目

Question

I'm doing a chat and I need to increment a list with the messages sent though I am unable to do.

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_janela);
    ArrayList<String> mensagens = new ArrayList<String>();
    ArrayAdapter<String> adapter = 
        new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, mensagens);
    ListView lv = (ListView)findViewById(R.id.lista);
    lv.setAdapter(adapter);
}

This method below I get the message text and is where I wanted to increase the list.

private void escreve(String texto) {
    mensagens.add(texto);
}

I hope it has become clear , thanks for attention

Answer 1

Declare both arralist and adapter outside and then just notify when data changed so it will work, check below solution.

  ArrayList<String> mensagens;
  ArrayAdapter<String> adapter;

  protected void onCreate(Bundle savedInstanceState) 
  {
     super.onCreate(savedInstanceState);
     setContentView(R.layout.activity_janela);
     mensagens = new ArrayList<String>();
     adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, mensagens);
     ListView lv = (ListView)findViewById(R.id.lista);
     lv.setAdapter(adapter);
}


 private void escreve(String texto) {
      mensagens.add(texto);
      adapter.notifyDataSetChanged();
  }

Answer 2

Your error: You cannot create a list as local variable in one method and use it in another. You have to make mensages a class variable.

Answer 3

If I understand correctly, you need a member variable.

And you can add to an ArrayAdapter directly without needing to notifyDatasetChanged

private ArrayAdapter<String> adapter;

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_janela);
    ArrayList<String> mensagens = new ArrayList<String>();
    adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, mensagens);
    ... 

private void escreve(String texto) {
    adapter.add(texto);
}