Author: Zoran Vučenović

DateTimeControls Package for Lazarus

http://wiki.lazarus.freepascal.org/DateTimeControls_Package

The DateTimeControls package contains two controls:

TDateTimePicker

TDBDateTimePicker

Author

Zoran Vučenović

License

Modified LGPL, same as Lazarus component library.

Introduction

Delphi's VCL has a control named TDateTimePicker, which I find very useful for editing dates. LCL, however, does not have this control. Instead, for editing dates LCL has a control named TDateEdit, but I prefer the VCL's TDateTimePicker.

Therefore, I tried to create a cross-platform Lazarus control which would resemble VCL's TDateTimePicker as much as possible.

The TDateTimePicker control does not use native Win control. It descends from LCL's TCustomControl to be cross-platform. It has been tested on Windows with win32/64 and qt widgetsets, as well as on Linux with qt and gtk2 widgetsets.

Note that the TDateTimePicker control does not descend from TEdit, so it does not have unnecessary caret. The VCL's control doesn't have caret either.

TDateTimePicker

Properties:

I'll explain some properties of TDateTimePicker control:

DateTime: TDateTime (public)

The DateTime value displayed on the control. This property is not published in object inspector, but its value is actually the same as Date and Time properties composed in one value. This property is provided to allow setting or reading of both date and time value at once in program code. In design time, Date and Time can be set in object inspector. There is also component editor which provides easy way of setting this property in design time.

Date: TDate

The date displayed on the control which the user can edit.

Time: TTime

The time displayed on the control which the user can edit.

MinDate: TDate

The minimal date user can enter.

MaxDate: TDate

The maximal date user can enter.

NullInputAllowed: Boolean

When True, the user can set the date to NullDate constant by pressing N key.

CenturyFrom: Word

When user enters the year in two-digit format, then the CenturyFrom property is used to determine which century the year belongs to. The default is 1941, which means that when two digit years is entered, it falls in interval 1941 – 2040. Note that MinDate and MaxDate properties can also have influence on the decision – for example, if the CenturyFrom is set to 1941 and MaxDate to 31. 12. 2010, if user enters year 23, it will be set to 1923, because it can’t be 2033, due to MaxDate limit.

Kind: TDateTimeKind

type TDateTimeKind = (dtkDate, dtkTime, dtkDateTime);

The control displays only date, only time or both.

DateMode: TDTDateMode

type TDTDateMode = (dmComboBox, dmUpDown, dmNone);

When DateMode is set to dmComboBox, there is a button on the right side of the control. When user clicks the button, the calendar control is shown, allowing the user to pick the date. When set to dmUpDown, then UpDown buttons are shown.

In my opinion the UpDown buttons aren't really useful in this control, they are provided for compatibility with Delphi's TDateTimePicker. Up and down keys can always serve for same purpose, so can mouse wheel.

In the next picture the first control's DateMode is set to dmComboBox and the second control's to dmUpDown.

If DateMode is dmComboBox, when the user clicks on the button a calendar drops down, allowing the user to pick a date.

Note: if Kind property is set to dtkTime, the calendar control is pointless. Therefore, if DateMode is dmComboBox, the UpDown is shown instead.

ShowCheckBox: Boolean

When set, there is a check box on the left side of the control. When unchecked, the display appears grayed and user interaction with the date or time is not possible. (The control is still enabled, though, only in sense that the check box remains enabled).

Checked: Boolean

If ShowCheckBox is set to True, this property determines whether the check box is checked or not. If ShowCheckBox is False, this property has no purpose and is automatically set to True.

DateDisplayOrder: TDateDisplayOrder

type TDateDisplayOrder = (ddoDMY, ddoMDY, ddoYMD, ddoTryDefault);

Defines the order for displaying day, month and year part of the date. When ddoTryDefault is set, then the controls tries to determine the order from ShortDateFormat global variable.

This is similar to DateEdit's DateOrder property.

DateSeparator: String

Defines the string used to separate date, month and year date parts. Setting this property automatically sets the UseDefaultSeparators property to False. To ensure that date and time separators are set to user's system defaults, set UseDefaultSeparators property to True.

TimeSeparator: String

Defines the string used to separate hour, minute, second and millisecond time parts. Setting this property automatically sets the UseDefaultSeparators property to False. To ensure that date and time separators are set to user's system defaults, set UseDefaultSeparators property to True.

UseDefaultSeparators: Boolean

When this property is set to True, then the DateSeparator and TimeSeparator properties will be set to DateSeparator and TimeSeparator global variables, which are set to user system defaults when application initializes.

TrailingSeparator: Boolean

When set to True, then the DateSeparator is shown once more, after the last date part. This property exists because in some languages the correct date format is 31. 1. 2010. including the last point, after the year.

LeadingZeros: Boolean

Determines whether the date and time parts are displayed with or without leading zeros (this actually affects day, month and hour parts of date and time display).

TimeDisplay: TTimeDisplay

type TTimeDisplay = (tdHM, tdHMS, tdHMSMs);

If Kind is dtkTime or dtkDateTime, then TimeDisplay value of tdHM means that only hours and minutes are displayed, tdHMS adds displaying of seconds and value of tdHMSMs means that milliseconds are displayed too.

TimeFormat: TTimeFormat

type TTimeFormat = (tf12, tf24);

The value of tf12 sets the display of time to 12 hours format, with AM/PM string and tf24 sets to 24 hours format.

TextForNullDate: String

Text which appears when the null date is set and control does not have focus. When control is focused, the text changes to defined format, but displaying zeros for date, and nines for time (for example "00/00/0000 99:99:99"), which is appropriate to user input. User can set the date to NullDate by pressing N key, provided NullInputAllowed property is True.

When TextForNullDate is set to empty string, zeros/nines format is displayed even when control does not have focus. If you want empty display, this can be achieved by setting TextForNullDate to one or more space characters.

AutoAdvance: Boolean

When true, then when user is entering valid text, the selection automatically advances to next part of date/time. The default is False because of compatibility with previous version, but switching on this option makes user interaction easier, this is a useful option and I recommend setting this property to true.

Cascade: Boolean

When true, then when user is increasing or decreasing one date/time part (using up-down keys or mouse wheel), it can increase or decrease by one another date/time part. For example, when date is 31.08.2013. and user increases the day, the day becomes 1 and month increases by one and becomes 9, so the date becomes 01.09.2013. If Cascade were set to False, the month would not change and the date would become 01.08.2013.

AutoButtonSize: Boolean

When true, the width of the arrow button (or up-down control, if it is shown instead) is automatically adjusted proportionally to the height.

HideDateTimeParts: TDateTimeParts

type

TDateTimePart = (dtpDay, dtpMonth, dtpYear, dtpHour, dtpMinute, dtpSecond, dtpMiliSec, dtpAMPM);

TDateTimeParts = set of dtpDay..dtpMiliSec;

With HideDateTimeParts property, you can chose which date/time parts will not be shown. Most of the time you do not need to use this property and you can get the format you want by using other properties (see Kind, TimeDisplay). However, if you need more control (for example, you might want to let user edit only days, months and hours), you can additionally hide any date/time parts with this control. Keep in mind that, with this property, you cannot show any date/time part which is hidden by another property (for example, if TimeDisplay is tdHM, the second part is not shown, regardless of this property).

TDBDateTimePicker

TDBDateTimePicker is a data-aware version of TDateTimePicker, with nice way of handling null database values.

#### Displaying null values

  When the underlying DB field has null value, then:

-   When the control gets focus, the text changes to defined format, but displaying zeros for date parts and nines for time parts (for example "00/00/0000 99:99:99"), which is appropriate to user input.
-   When the control is not focused, then it displays the text defined in TextForNullDate property. The default is "NULL".

#### Setting the field value to null

  If NullInputAllowed property is True, the user can set the date and time to null, by pressing N key.

DateTimePicker Editor

DateTimePicker Editor is a dialog which provides easy way to set Date, Time, MinDate and MaxDate properties in design time. It is invoked when DateTimePicker control is double-clicked in form designer. It is also shown when the ellipsis (…) button, shown in Date, Time, MinDate and MaxDate properties in Object inspector, gets clicked.

Tips

Q: When the date/time value is null, how to display zeros/nines in user format, no matter whether the control is focused or not?

A: Set TextForNullDate property to empty string. If TextForNullDate is set to empty string, then zeros/nines are displayed, same as when the control has focus.

Q: When the date/time value is null, If empty string in TextForNullDate property actually sets the display to zeros/nines format, how to set the control to display nothing?

A: Set TextForNullDate property to one space character, you will get the empty display.