Change the Date

app/src/main/java/dragosholban/com/timezoneconverter/DatePickerFragment.java

@@ -0,0 +1,28 @@
package dragosholban.com.timezoneconverter;

import android.app.DatePickerDialog;
import android.app.Dialog;
import android.app.DialogFragment;
import android.os.Bundle;
import android.widget.DatePicker;

import java.util.Calendar;
import java.util.Date;

public class DatePickerFragment extends DialogFragment implements DatePickerDialog.OnDateSetListener {

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        Calendar c = Calendar.getInstance();
        int year = c.get(Calendar.YEAR);
        int month = c.get(Calendar.MONTH);
        int day = c.get(Calendar.DAY_OF_MONTH);

        return new DatePickerDialog(getActivity(), this, year, month, day);
    }

    @Override
    public void onDateSet(DatePicker datePicker, int year, int month, int day) {
        ((MainActivity) getActivity()).setLocalDate(new Date(year - 1900, month, day));
    }
}

app/src/main/java/dragosholban/com/timezoneconverter/MainActivity.java

@@ -1,14 +1,19 @@
package dragosholban.com.timezoneconverter;

import android.app.DialogFragment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.SeekBar;
import android.widget.TextView;

import java.text.DateFormat;
import java.util.Date;

public class MainActivity extends AppCompatActivity {
    Date localDate = new Date();
    Button dateBtn;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
@@ -39,5 +44,24 @@ public void onStopTrackingTouch(SeekBar seekBar) {
            }
        });
        seekBar.setProgress(localDate.getHours());

        dateBtn = findViewById(R.id.dateButton);
        dateBtn.setText(DateFormat.getDateInstance().format(localDate));
    }

    public void showDatePicker(View view) {
        DialogFragment dialog = new DatePickerFragment();
        dialog.show(getFragmentManager(), "datePicker");
    }

    public void setLocalDate(Date date) {
        // we need to keep the time on the date unchanged
        int hours = localDate.getHours();
        int minutes = localDate.getMinutes();
        localDate = date;
        localDate.setHours(hours);
        localDate.setMinutes(minutes);
        Button dateBtn = findViewById(R.id.dateButton);
        dateBtn.setText(DateFormat.getDateInstance().format(localDate));
    }
}

app/src/main/res/layout/activity_main.xml

@@ -27,6 +27,7 @@
        android:layout_marginBottom="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:onClick="showDatePicker"
        android:text="Date"
        app:layout_constraintBottom_toTopOf="@+id/timeZoneButton"
        app:layout_constraintEnd_toEndOf="parent"