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"