How to keep a Textview text after the App closes

Question

Good, I’m new to Android, but I would like to know how I can keep/save the information that is in a Textview, so that this is not deleted when close application.

     public class Activity extends AppCompatActivity {
        Calendar c = Calendar.getInstance();
        SimpleDateFormat sdf = new SimpleDateFormat("dd:MMMM:yyyy HH:mm:ss");
        String strDate = sdf.format(c.getTime());

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

               private void EscreverData(){
                  TextView datas = (TextView) findViewById(R.id.datas);
                  datas.append(strDate);}}

Basically what I want is, when this activity starts, get the date and time and show this information in Textview. However, I would like her to continue storing the old dates and not erase them each time the activity is started again. I’ve tried searching a little and I think a good solution could be Sharedpreferences but I don’t know how to use it. Thanks if you can help me

Answer 1

A simple form of data persistence is to use the SharedPreference as shown in the documentation on How to save key value sets. Below is an example of how to save, considering you have any variable with any text:

String value = "Um texto qualquer";
SharedPreferences sharedpreferences = getSharedPreferences("pref", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedpreferences.edit();
editor.putString("str_textview", value);
editor.commit();

To rescue:

SharedPreferences pref = getSharedPreferences("pref", MODE_PRIVATE);
String text = pref.getString("str_textview", null);
meuTextView.setText(text );

See more details on this question about Save value in Sharedpreference.

This way, at any time of its application, it is possible to return the value that was saved in a certain key. See here Data Persistence Levels in Android Applications other approaches.

In the Kotlin would look like this:

val value = "Um texto qualquer"
val sharedpreferences = context.getSharedPreferences("pref", Context.MODE_PRIVATE)
val editor = sharedpreferences.edit()
editor.putString("str_textview", value)
editor.commit()

To rescue:

val pref = context.getSharedPreferences("pref", MODE_PRIVATE)
val text = pref.getString("str_textview", null)
myTextView.setText(text)