Android DatePicker Demonstration

Screenshot of the app running in the Gingerbread emulator

Note the way that the set, before and add methods of the Calendar object supports the use of the DatePicker object. You can compare this code with the RemObjects C# version below it.

The code of MainActivity.pas

namespace org.me.android_datepicker;

interface

uses
  java.util,
  android.app,
  android.content,
  android.os,
  android.util,
  android.view,
  android.widget;

type
  MainActivity = public class(Activity)
  private
    dp : DatePicker;
    tv : TextView;
  public
    method onCreate(savedInstanceState: Bundle); override;
    method DateChange(v : View; year: Integer; monthOfYear: Integer; dayOfMonth: Integer);
  end;

implementation

method MainActivity.DateChange(v : View; year, monthOfYear, dayOfMonth: Integer);
var
  DaysUntil : Integer := 0;
  calToday, calDP_Date : Calendar;
begin
  calToday :=  Calendar.getInstance;
  calDP_Date :=  Calendar.getInstance;
  //Set date and time of target date to midnight on date of DatePicker.
  calDP_Date.set(year, monthOfYear, dayOfMonth, 0, 0, 0);
  while calToday.before(calDP_Date) do
    begin 
      calToday.add(Calendar.DAY_OF_MONTH, 1);
      inc(DaysUntil);
    end;
  //Output the number of days we are before the target. 
  tv.Text := 'Days to wait: ' + DaysUntil.toString;
end;

method MainActivity.onCreate(savedInstanceState: Bundle);
var
  DaysUntil : Integer := 0;
  odcListener : DatePicker.OnDateChangedListener;
begin
  inherited;
  // Set view from the "main" layout resource.
  ContentView := R.layout.main;
  //Assign DatePicker and TextView.
  dp := DatePicker(findViewById(R.id.dp1));
  tv := TextView(findViewById(R.id.tv1));
  //Assign OnDateChangedListener.
  odcListener := new interface DatePicker.OnDateChangedListener(onDateChanged := @DateChange);
  //Set to date of DatePicker to Christmas Eve, 2012.
  dp.init(2012, 11, 24, odcListener);  
end;
end.

Layout File

<?xml version="1.0" encoding="utf-8"?>
  <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:gravity="center_horizontal">
    <DatePicker
      android:id="@+id/dp1"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content" />
    <TextView
      android:id="@+id/tv1"
      android:textSize="18sp"
      android:textColor="#00FF00"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_below="@+id/dp1" 
      android:text="@string/instruction" />
  </RelativeLayout>

Strings File

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <string name="app_name">Date Picker</string>
  <string name="instruction">Change target date to see days to wait.</string>
</resources>

RemObjects C# Version of Android DatePicker Demonstration

using java.util;
using android.app;
using android.content;
using android.os;
using android.util;
using android.view;
using android.widget;

namespace org.me.android_datepicker_cs
{
  public class MainActivity: Activity
  {
    private DatePicker dp;
    private TextView tv;

    public void DateChange(View v, Integer year, Integer monthOfYear,Integer  dayOfMonth)
    {
      Integer DaysUntil = 0;
      Calendar calToday, calDP_Date;
      calToday =  Calendar.getInstance();
      calDP_Date =  Calendar.getInstance();
      //Set date and time of target date to midnight on date of DatePicker.
      calDP_Date.set(year, monthOfYear, dayOfMonth, 0, 0, 0);
      while (calToday.before(calDP_Date))
      { 
          calToday.add(Calendar.DAY_OF_MONTH, 1);
          inc(DaysUntil);
      }
      //Output the number of days we are before the target. 
      tv.Text = "Days to wait: " + DaysUntil.toString();
    }

    public override void onCreate(Bundle savedInstanceState)
    {
      base.onCreate(savedInstanceState);
      // Set our view from the "main" layout resource
      ContentView = R.layout.main;
      //Assign DatePicker and TextView.
      dp = (DatePicker)(findViewById(R.id.dp1));
      tv = (TextView)(findViewById(R.id.tv1));
      //Set to date of DatePicker to Christmas Eve, 2014.
      dp.init(2014, 11, 24, DateChange);  
    }
  }
}