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Using Pickers to Provide Platform-Specific Behavior and View of Selection Controls

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FireMonkey defines the pickers to provide the platform-specific engine introducing selection controls with the native view and native behavior under different platforms.

For example, Windows and OS X provide a standard desktop calendar control for date selection:

Calendar control for date selection

On the other hand, iOS and Android provide platform-specific controls for date selection:

iOS Android
Rotating wheels for date selection FMX Android DateTimePicker.png

Also, time picker is supported for Android and iOS:

iOS Android
Time Picker iOS.png Time Picker Android.png

In the FireMonkey framework, you can use pickers to provide platform-specific view and behavior of date selection controls.

The core of the pickers engine is declared in the FMX.Pickers unit. The Pickers unit declares the IFMXPickerService interface introducing the so-called platform service (see FireMonkey Platform Services). Also, the Pickers unit introduces two pickers:

  • Date-Time picker: a platform-specific control, of the TCustomDateTimePicker type, supporting selection of date.
  • List picker: a platform-specific control, of the TCustomListPicker type, supporting selection of strings from a drop-down list.

These pickers can be activated on different platforms using the IFMXPickerService service.

To use the IFMXPickerService service:

  1. Check whether the IFMXPickerService platform service is supported by the current platform and retrieves the PickerService pointer to the IFMXPickerService service object.
  2. Either create a TCustomDateTimePicker instance using the CreateDateTimePicker method or create a TCustomListPicker picker instance using the CreateListPicker method:


Delphi:

     var
       PickerService: IFMXPickerService;
     begin
        if PlatformServices.Current.SupportsPlatformService(IFMXPickerService, Interface(PickerService))
     then
         FDateTimePicker := PickerService.CreateDateTimePicker;
         ...   // or
         FListPicker := PickerService.CreateListPicker;

C++:

        _di_IFMXPickerService PickerService;
	TCustomDateTimePicker* FDateTimePicker;
	TCustomListPicker* FListPicker ;
	if (TPlatformServices::Current->SupportsPlatformService
		(__uuidof(IFMXPickerService))) {
		PickerService = TPlatformServices::Current->GetPlatformService
			(__uuidof(IFMXPickerService));
		FDateTimePicker = PickerService->CreateDateTimePicker();
                ... //or 
		FListPicker = PickerService->CreateListPicker();
      }
See FireMonkey Platform Services for more information about how to use platform services. See the code of FMX.CalendarEdit.TCustomCalendarEdit.Create and FMX.ListBox.TCustomComboBox.Create for more examples.
  1. Show the required picker calling the Show methods from created objects of TCustomDateTimePicker or TCustomListPicker classes and setting the appropriate parameters and event handlers to these objects. For example:

Delphi:

      FDateTimePicker: TCustomDateTimePicker;
      //...
      FDateTimePicker.Date := Date;
      FDateTimePicker.FirstDayOfWeek := TCalDayOfWeek.dowMonday;
      FDateTimePicker.ShowWeekNumbers := True;
      FDateTimePicker.TodayDefault := False;
      FDateTimePicker.Show;

C++:

        TCustomDateTimePicker* FDateTimePicker;
        //...
	FDateTimePicker->Date = Date();
        FDateTimePicker->FirstDayOfWeek = TCalDayOfWeek(0);
	FDateTimePicker->ShowWeekNumbers = true;
	FDateTimePicker->TodayDefault = false;
	FDateTimePicker->Show();
For more examples, see the code of FMX.CalendarEdit.Style.TStyledCalendarEdit.DropDown and FMX.ListBox.TCustomComboBox.DropDown.

These pickers provide the platform-specific behavior of corresponding control elements. For example, FMX.ListBox.TComboBox under Windows 8 centers a drop-down list on the selected element:

Centered List for date selection

To implement a centered date selection list for a Metropolis UI (Windows 8) application, use the following steps:

  1. Create a FireMonkey Metropolis UI Application.
  2. From the Tool Palette, add a TComboBox.
  3. In the Form Designer, select your TComboBox.
  4. In the Object Inspector, set the FMX.ListBox.TComboBox.DropDownKind property to Native.
  5. For Windows 8, the FMX.Styles.TStyleDescription property should provide the [METROPOLISUI] platform. To guarantee this behavior:
    1. In the Structure pane, double-click the StyleBook1 item and then select the styleDescription.TStyleDescription property.
    2. In the Object Inspector, the PlatformTarget property defines platforms for which this style can be implemented. Check that PlatformTarget contains the [METROPOLISUI] platform.
      If you do not specify the [METROPOLISUI] platform, then the data selection control works as a standard (either Windows or OS X) drop-down list without centering on the selected element.

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