Jaa

Android Date Picker

  • Artikkeli

Overview

There are occasions when a user must input data into an Android application. To assist with this, the Android framework provides the DatePicker widget and the DatePickerDialog . The DatePicker allows users to select the year, month, and day in a consistent interface across devices and applications. The DatePickerDialog is a helper class that encapsulates the DatePicker in a dialog.

Modern Android applications should display the DatePickerDialog in a DialogFragment. This will allow an application to display the DatePicker as a popup dialog or embedded in an Activity. In addition, the DialogFragment will manage the lifecycle and display of the dialog, reducing the amount of code that must be implemented.

This guide will demonstrate how to use the DatePickerDialog, wrapped in a DialogFragment. The sample application will display the DatePickerDialog as a modal dialog when the user clicks a button on an Activity. When the date is set by the user, a TextView will update with the date that was selected.

Screenshot of Pick Date button followed by Date Picker dialog

Requirements

The sample application for this guide targets Android 4.1 (API level 16) or higher, but is applicable to Android 3.0 (API level 11 or higher). It is possible to support older versions of Android with the addition of the Android Support Library v4 to the project and some code changes.

Using the DatePicker

This sample will extend DialogFragment. The subclass will host and display a DatePickerDialog:

Closeup of Date Picker dialog

When the user selects a date and clicks the OK button, the DatePickerDialog will call the method IOnDateSetListener.OnDateSet. This interface is implemented by the hosting DialogFragment. If the user clicks the Cancel button, then fragment and dialog will dismiss themselves.

There are several ways the DialogFragment can return the selected date to the hosting activity:

  1. Invoke a method or set a property – The Activity can provide a property or method specifically for setting this value.

  2. Raise an event – The DialogFragment can define an event that will be raised when OnDateSet is invoked.

  3. Use an Action – The DialogFragment can invoke an Action<DateTime> to display the date in the Activity. The Activity will provide the Action<DateTime when instantiating the DialogFragment. This sample will use the third technique, and require that the Activity supply an Action<DateTime> to the DialogFragment.

Extending DialogFragment

The first step in displaying a DatePickerDialog is to subclass DialogFragment and have it implement the IOnDateSetListener interface:

public class DatePickerFragment : DialogFragment, 
                                  DatePickerDialog.IOnDateSetListener
{
    // TAG can be any string of your choice.
    public static readonly string TAG = "X:" + typeof (DatePickerFragment).Name.ToUpper();
    
    // Initialize this value to prevent NullReferenceExceptions.
    Action<DateTime> _dateSelectedHandler = delegate { };
    
    public static DatePickerFragment NewInstance(Action<DateTime> onDateSelected)
    {
        DatePickerFragment frag = new DatePickerFragment();
        frag._dateSelectedHandler = onDateSelected;
        return frag;
    }
    
    public override Dialog OnCreateDialog(Bundle savedInstanceState)
    {
        DateTime currently = DateTime.Now;
        DatePickerDialog dialog = new DatePickerDialog(Activity, 
                                                       this, 
                                                       currently.Year, 
                                                       currently.Month - 1,
                                                       currently.Day);
        return dialog;
    }
    
    public void OnDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth)
    {
        // Note: monthOfYear is a value between 0 and 11, not 1 and 12!
        DateTime selectedDate = new DateTime(year, monthOfYear + 1, dayOfMonth);
        Log.Debug(TAG, selectedDate.ToLongDateString());
        _dateSelectedHandler(selectedDate);
    }
}

The NewInstance method is invoked to instantiate a new DatePickerFragment. This method takes an Action<DateTime> that will be invoked when the user clicks on the OK button in the DatePickerDialog.

When the fragment is to be displayed, Android will call the method OnCreateDialog. This method will create a new DatePickerDialog object and initialize it with the current date and the callback object (which is the current instance of the DatePickerFragment).

Note

Be aware that the value of the month when IOnDateSetListener.OnDateSet is invoked is in the range of 0 to 11, and not 1 to 12. The day of the month will be in the range of 1 to 31 (depending on which month was selected).

Showing the DatePickerFragment

Now that the DialogFragment has been implemented, this section will examine how to use the fragment in an Activity. In the sample app that accompanies this guide, the Activity will instantiate the DialogFragment using the NewInstance factory method and then display it invoke DialogFragment.Show. As a part of instantiating the DialogFragment, the Activity passes an Action<DateTime>, which will display the date in a TextView that is hosted by the Activity:

[Activity(Label = "@string/app_name", MainLauncher = true, Icon = "@drawable/icon")]
public class MainActivity : Activity
{
    TextView _dateDisplay;
    Button _dateSelectButton;

    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);
        SetContentView(Resource.Layout.Main);

        _dateDisplay = FindViewById<TextView>(Resource.Id.date_display);
        _dateSelectButton = FindViewById<Button>(Resource.Id.date_select_button);
        _dateSelectButton.Click += DateSelect_OnClick;
    }

    void DateSelect_OnClick(object sender, EventArgs eventArgs)
    {
        DatePickerFragment frag = DatePickerFragment.NewInstance(delegate(DateTime time)
                                                                 {
                                                                     _dateDisplay.Text = time.ToLongDateString();
                                                                 });
        frag.Show(FragmentManager, DatePickerFragment.TAG);
    }
}

Summary

This sample discussed how to display a DatePicker widget as a popup modal dialog as a part of an Android Activity. It provided a sample DialogFragment implementation and discussed the IOnDateSetListener interface. This sample also demonstrated how the DialogFragment may interact with the host Activity to display the selected date.