Author: Daniel Wischnewski
Sometimes, when you create components, you want to make it easier for the
developers to use them. This is the time to develop a property editor.
Answer:
INTRODUCTION
In this article I will give you a short introduction to property editor
development. This property editor developed here will simlpy allow you to edit
string and TCaption properties in a better way, allowing you to add line breaks to
strings.
There are two reasons for this property editor. First it is great to add line
breaks into the labels caption, second it is fairly simple, therefore a good start
for developing a property editor.
STEPS IN CREATING A PROPERTY EDITOR
First a short list of considerations when creating a property editor.
How should the property editor support the developer?
Which components/properties/data types should the editor support?
When do you have enough time to write it? :)
How do we support the developer?
Well, as I have written before, we will give the developer a simple way of adding
line breaks to. The form we will create with the Delphi form designer, jsut as we
do always. We add a public procedure to it, that will take the old value, load it
into a memo field, show the form and return the either new value or the old if the
user has not confirmed the changes.
Which components/properties/data are supported?
We will support all components and properties of the types string and TCaption.
DESIGING THE FORM
Start Delphi and close all open files. Create a new form and name it
frmStringEditor. Add a memo field to the form and name it mmoStringProperty. Now we
need to buttons, one for "OK" and one for "Cancel." Thats all for the design part.
Make it fit "nicely." Add event handlers to the to button click procedures!
We will add one public procedure that will accomplish the form show and decide,
whether the property is changed or not.
function Edit(var Data: string): Boolean;
The remaining code comes a little later.
CREATING THE PROPERTY EDITOR CLASS
All Property Editors have to be a descendend of the TPropertyEditor class. In our
case we will descend from the TStringProperty class, that itself descends from the
one previously named.
There are two function we need to override. GetAttributes to tell Delphi that we
provide a dialog to manipulate the property. Edit is the function called when the
developer calls for the property editor dialog.
1 TOurStringProperty = class(TStringProperty)
2 public
3 function GetAttributes: TPropertyAttributes; override;
4 procedure Edit; override;
5 end;
The remaining code comes a little later, too.
REGISTERING THE PROPERTY EDITOR
We will install the property editor just like we install components, therefore we
have to provide the Register property. In the body we will add a call to the
RegisterPropertyEditor function. This function takes four parameters.
Information about the property type handled by the editor
The component/control class this editor is for (nil for all)
The property this editor is for ('' for all)
The property editor class itself
AND NOW THE WHOLE CODE
I have placed this all into one unit developed on Delphi 5 and tested with Delphi 6
Evaluation version. You will need at least the Professional Editions to get it
working. Earlier versions of Delphi should work just fine. Cannot test on them,
sorry.
This unit assumes that you saved your form under the name of uStringEditor.
6
7 unit uStringEditor;
8
9 interface
10
11 uses
12 Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
13 StdCtrls, TypInfo
14 {$IFNDEF VER140}
15 , DsgnIntf
16 {$ELSE}
17 , DesignEditors, DesignIntf
18 {$ENDIF}
19 ;
20
21 type
22 TfrmStringEditor = class(TForm)
23 mmoStringProperty: TMemo;
24 btnOK: TButton;
25 btnCancel: TButton;
26 procedure btnOKClick(Sender: TObject);
27 procedure btnCancelClick(Sender: TObject);
28 private
29 public
30 function Edit(var Data: string): Boolean;
31 end;
32
33 TOurStringProperty = class(TStringProperty)
34 public
35 function GetAttributes: TPropertyAttributes; override;
36 procedure Edit; override;
37 end;
38
39 procedure register;
40
41 implementation
42
43 {$R *.DFM}
44
45 procedure register;
46 begin
47 RegisterPropertyEditor(TypeInfo(TCaption), nil, '', TOurStringProperty);
48 RegisterPropertyEditor(TypeInfo(string), nil, '', TOurStringProperty);
49 end;
50
51 function EditConnectionString(
52 Component: TComponent; PropInfo: PPropInfo
53 ): Boolean;
54 var
55 Str: string;
56 begin
57 Result := False;
58 with TfrmStringEditor.Create(Application) do
59 try
60 Caption := Format('%s.%s string editor', [Component.Name, PropInfo^.Name]);
61 Str := GetStrProp(Component, PropInfo);
62 if Edit(Str) then
63 begin
64 SetStrProp(Component, PropInfo, Str);
65 Result := True;
66 end;
67 finally
68 Free;
69 end;
70 end;
71
72 { TOurStringProperty }
73
74 procedure TOurStringProperty.Edit;
75 begin
76 if EditConnectionString(GetComponent(0) as TComponent, GetPropInfo)
77 then
78 Modified;
79 end;
80
81 function TOurStringProperty.GetAttributes: TPropertyAttributes;
82 begin
83 Result := [paDialog];
84 end;
85
86 { TfrmStringEditor }
87
88 procedure TfrmStringEditor.btnCancelClick(Sender: TObject);
89 begin
90 ModalResult := mrCancel;
91 end;
92
93 procedure TfrmStringEditor.btnOKClick(Sender: TObject);
94 begin
95 ModalResult := mrOk;
96 end;
97
98 function TfrmStringEditor.Edit(var Data: string): Boolean;
99 begin
100 mmoStringProperty.Text := Data;
101 if ShowModal = mrOK then
102 begin
103 Result := Data <> mmoStringProperty.Text;
104 Data := mmoStringProperty.Text;
105 end
106 else
107 begin
108 Result := False;
109 end;
110 end;
111
112 end.
INSTALLING IT
Go to the menu Component | Install Component..., select the your file from the disk and press "OK." After compiling and saving the package you are finished. You may have to restart Delphi for the changes to take place.
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