Transcript Creating Custom .NET Controls in Delphi

Creating Custom Microsoft .NET
Framework Controls in Delphi
Ray Konopka
Agenda
 .NET Component Model
 Comparing the FCL to the VCL
 Custom Events
 Custom Painting
 Component Related Attributes
 Sample Control
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.NET Component Model
 Defined in the System.ComponentModel
namespace
 Includes

System.ComponentModel.Component declaration

Common Delegates

Component Related Attribute declarations

Licensing Classes

Design-time Support Classes
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Component Class
 System.ComponentModel.Component provides
the base implementation of IComponent in the FCL
 Defines the following properties

DesignMode

Container

Site

Events
 Descend from
System.ComponentModel.Component to create
a nonvisual component
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Two Control Classes in .NET
 Most visual controls in .NET will descend from one of
two classes:
 System.Windows.Forms.Control

Base WinForms Control class

Most similar to existing component models (e.g. VCL)

Rendering handled through Graphics class (i.e. GDI+)
 System.Web.UI.Control


Base ASP.NET Server Control class
Renders markup text used by a client’s browser or
viewing device to display visual elements.
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System.Windows.Forms.Control
 Implements basic functionality for visualization
 Defines the control’s bounds (i.e. its Position and
Size)
 Provides a window handle (Handle)
 Provides access to keyboard events
 Provides access to mouse events
 Provides access to paint events
 Supports ambient properties

Cursor, Font, BackColor, ForeColor, RightToLeft.
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Comparing the FCL to the VCL
 FCL is quite similar to the VCL, but there are
significant differences
 No equivalent to TGraphicControl
 Actually, no TWinControl or TCustomControl
classes either
 System.Windows.Forms.Control is more like
TCustomControl than TControl
 Significantly fewer TCustomXxxx class

called XxxxBase in FCL
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Where is the Align property?
 Most of the functionality implemented in the VCL base classes
is available in the base FCL classes
 However, there are many property name changes

Align
 Dock

Caption
 Text

Color
 BackColor

Font.Color
 ForeColor

PopupMenu  ContextMenu

ModalResult  DialogResult

etc.
 Tag is an Object
 ParentXxxx properties replaced with ambient properties
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Control Styles
 TControl.ControlStyle replaced with
GetStyle/SetStyle method pair
SetStyle( ControlStyles.ResizeRedraw, True );
SetStyle( ControlStyles.Opaque, True );
// Double
SetStyle(
SetStyle(
SetStyle(
Buffering
ControlStyles.UserPaint, True );
ControlStyles.AllPaintingInWmPaint, True );
ControlStyles.DoubleBuffer, True );
 Some, but not all, styles have corresponding public
properties

ResizeRedraw
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Component Notifications
 Component notifications allow descendants to react
to state changes implemented in an ancestor class
 In the VCL, a component responds to notifications by
handling special messages

e.g. cm_EnabledChanged
 In .NET, a component responds to notifications by
overriding a method

OnEnabledChanged Event Dispatch Method
 .NET even surfaces component notifications as public
events

EnabledChanged Event
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FCL and VCL Events
 Unfortunately, the naming convention used for events
in the FCL is opposite that used in the VCL
 In the VCL…

OnPaint is the event

Paint is the event dispatch method
 In the FCL…

OnPaint is the event dispatch method

Paint is the event
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FCL and VCL Events
 Please Note:

Unfortunately, it is common in .NET literature to see
statements like
 “…take a look at the OnPaint event handler…”

Problem is that base (ancestor) does not get called
and thus the real event never gets raised
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Events
 Events allow customization through delegation
 Events are properties
 Implemented using Delegates
 Events are optional
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Creating a Custom Event
 Determine the action that triggers event
 Define the event type (i.e. the Delegate)

Specifies the parameters that will be sent to an event
handler
 Declare the event property

Singleton Event (read/write)

Multicast Event (add/remove)
 Dispatch the event when it occurs.
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Determine Event Trigger
 Events allow developers to “hook” into normal
processing
 Example

Generate a ValueChanged event when data
represented by the component changes
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Delegates
 The FCL utilizes Delegates to support events
 A delegate is a class that encapsulates a linked-list of
method pointers
 With delegates an event can be sent to multiple
subscribers
 Specify the parameters that will be sent to event
handlers.
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Define the Delegate
 May be possible to use predefined delegate

e.g. EventHandler
 First parameter always “object sender”
 Second parameter always EventArgs or descendant
 If you require passing additional parameters, you’ll
need to create a new EventArgs descendant
ValueChangingEventHandler =
procedure ( sender: System.Object;
e: ValueChangingEventArgs ) of object;
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Declare the Event Property
 Unlike the VCL, by convention event names in the
FCL do not start with “On”
// Multicast Event
property ValueChanged: EventHandler
add FValueChanged
remove FValueChanged;
// Singleton Event
property ValueChanging: ValueChangingEventHandler
read FValueChanging
write FValueChanging;
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Raise the Event
 Use an Event Dispatch Method
 In FCL, event dispatch methods start with “On”
 Usually defined as strict protected and virtual
 Calling the event (e.g. FValueChanged) causes all
of the event handlers in the delegate’s list to be
called
procedure RkSpinner.OnValueChanged( E: EventArgs );
begin
if Assigned( FValueChanged ) then
FValueChanged( Self, E );
end;
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Custom Painting
 Custom painting is supported by Graphics class (i.e.
GDI+)




System.Drawing
System.Drawing.Drawing2D
System.Drawing.Imaging
System.Drawing.Text
 GDI+ Features




Alpha Blending & Anti-Aliased 2D Drawing
Gradient Brushes
Universal Transformations & Floating Point coordinates
Support for more Image formats
 BMP, GIF, JPEG, PNG, TIFF, ICON, WMF, EMF.
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GDI+ Programming Model
 No more device contexts (DC) – Graphics Object
 GDI+ is Stateless


No more selecting pens and brushes into a DC
Pens, Brushes, etc. are passed to each GDI+ drawing
method
 Graphic elements are no longer drawn with both Pen
and Brush
 Draw methods use a Pen (eg. DrawRectangle)
 Fill methods use a Brush (eg. FillEllipse).
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GDI+ Programming Model
 Colors support Alpha Channels

ARGB format
 0x880000FF semi-transparent blue

A = 0x00 fully transparent

A = 0xFF fully opaque
 Rectangles, Points, etc. are classes

r.Inflate( 5, 5 );
// Instead of InflateRect( r, 5, 5 );
 Rectangles are defined differently!

Left, Top, Width, Height.
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GDI+ Programming Model
 Obtaining a Graphics Object

Passed to OnPaint methods in PaintEventArgs

Request one using Graphics.FromHwnd( Handle )

If utilizing double-buffering, do not use FromHwnd
 Cleaning Up

Dispose all GDI+ objects

Dispose Graphics object if requested via FromHwnd
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Attributes
 Attributes used to modify the behavior of properties,
methods, events
[ Category( 'Appearance' ),
Description( 'The width of buttons, in pixels.' ),
DefaultValue( 18 ) ]
property ButtonWidth: Integer
read FButtonWidth
write SetButtonWidth;
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Attributes
 Category
 Description
 Browsable
 DefaultValue
 DefaultProperty & DefaultEvent
 Localizable
 ToolboxBitmap
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Example
 RayKonopka.Delphi.Controls Assembly

RkSpinner Component
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References
 Microsoft Development Network (MSDN)
 Design Guidelines for Class Library Developers
 Developing Components
 Developing Windows Forms Controls
 Applied .NET Framework Development

Jeffrey Richter
 Programming Microsoft .NET

Jeff Prosise
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The Finish Line
 Contact Information
Ray Konopka
[email protected]
http://www.raize.com
 Evaluation Forms
 Questions & Answers
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