Basic ways to write controls in Delphi
As a Delphi programmer, it is necessary to further improve the programming level, you must master the preparation method of the control. This article will introduce some basic methods and patterns of the preparation of the preparation of the initiator through a simple example.
This example control is called TLEiLabel, which is to add two practical functions on the basis of TLabel: First, make the text with a stereo shape, and the other is to make the text have hyperlink attributes. Let's take a step by step to implement these features.
First, make the text have stereo shapes
First define type T3deffect and attribute Style3D as follows:
T3Deffect = (Normal, raised, lowered, shadowed);
Property Style3D: T3deffect Read FStyle3d Write SetStyle3d Default Normal
The variable is defined in private: "FStyle3D: T3deffect;" and sets the setStyle3D () method as follows, which is also a general format of writing methods:
Procedure Tleilabel.setStyle3D (Value: T3deffect);
Begin
IF fStyle3D <> Value Then
Begin
FStyle3d: = Value;
Invalidate; // means the control will be redrawn
END;
END;
In addition to the text of the shadow, the shadow is also defined Shadexoffset and ShadeyOffset:
Property ShadowxOffset: Integer Read FXOffset Write SetFxOffset Default 5;
Property Shadowyoffset: Integer Read Fyoffset Write SetFyoffset Default -5;
Write the method setFxOffset (), setFyOffset (), and SETSTYLE3D () above.
To redraw control, you generally have to overload the Paint method. Here is just heavy graphics, we only need to overload the DodrawText method.
DodrawText's statement is placed in protected:
Procedure DodrawText (Var Rect: Treat; Flags: longint); OVERRIDE;
Here DodrawText () draws different texts according to four types (normal, projections, recesses and shadows).
Second, make the text have hyperlink attributes
Define an attribute URL indicates the URL or Email address to be linked.
Property URL: String Read Furl Write SetURL;
Write the method seturl as follows:
Procedure tleilabel.seturl (value: string);
Begin
IF furl <> value kilure: = value;
IF furl <> '' THEN
Cursor: = crhandpoint;
END;
When you click this Label to open a browser or send and receive a mail tool, you have to overload the Click method.
Procedure Click; Override;
Procedure tleilabel.click;
Var s: string;
Begin
Inherited Click;
If FURL = '' Then EXIT;
IF LowerCase (Copy (FURL, 1, 7)) = 'http: //' Then
S: = FURL
Else IF POS ('@', furs) <> 0 THENS: = 'Mailto:' FURL
Else
S: = 'http://' furl;
Shellexecute (Application.handle, 'Open', PCHAR (S), NIL, NIL, SW_SHOWNORMAL);
END;
The general hyperlink is changed when the mouse is moved into the color. To this end, attribute HoverColor, indicating the color of the text when the mouse is moved.
Property HoverColor: Tcolor Read FhoverColor Write SthoverColor Default Clred;
Also defined two processes that receive Windows messages cm_mouseenter and cm_mouseeleave (mouse movement and removal):
Procedure CmmouseEnter (Var Message: TMESSAGE); Message Cm_MouseEnter;
Procedure CmmouseLeave (Var Message: TMESSAGE); Message Cm_MouseLeave;
Procedure tleilabel.cmmouseenter (Var message: tMessage);
Begin
IF enabled and visible and getparentform (self) .active then
Begin
FFONTCOLOR: = font.color;
// Save the color of the text
Font.color: = fhovercolor;
// change text color
END;
END;
Procedure Tleilabel.cmmouseLeave (Var Message: TMESSAGE);
Begin
Font.color: = ffontcolor;
// Restore the original color
END;
To set the default value of the properties, we also need to overload construct Create (), note, must first call the ancestry class. The procedure for heavy duty constructs CREATE () is as follows:
Constructor Tleilabel.create (Aowner: Tcomponent);
Begin
Inherited Create (Aowner);
// must first call the ancestral structure
FStyle3D: = Normal;
FXOFFSET: = 5;
Fyoffset: = -5;
FHOVERCOLOR: = CLRED;
END;
Finally, you must also add icon for this control. We can create a 24 × 24 Bitmap bitmap with Image Editor in Delphi, saved as a DCR file, the file name must be the same as the control's PAS file name, the bitmap name must be the same as the control name and all capitalize.
