Creating Custom Microsoft .NET Framework Controls in Delphi

1
Creating Custom Microsoft .NET Framework Controls
in Delphi
2
Agenda

• .NET Component Model
• Comparing the FCL to the VCL
• Custom Events
• Custom Painting
• Component Related Attributes
• Sample Control

3
.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 clients browser or
  viewing device to display visual elements.

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System.Windows.Forms.Control

• Implements basic functionality for visualization
• Defines the controls 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.

7
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
• Some, but not all, styles have corresponding
  public properties
• ResizeRedraw

SetStyle( ControlStyles.ResizeRedraw, True
) SetStyle( ControlStyles.Opaque, True ) //
Double Buffering SetStyle( ControlStyles.UserPaint
, True ) SetStyle( ControlStyles.AllPaintingInWmP
aint, True ) SetStyle( ControlStyles.DoubleBuffer
, True )
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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,
  youll 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 delegates 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
• Evaluation Forms
• Questions Answers

Ray Konopka rkonopka_at_raize.com http//www.raize.co
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