當(dāng)你在設(shè)計器中選擇一個組件時，組件屬性便顯示在對象檢查器中。你可以為屬性創(chuàng)建你自己的編輯器。例如，“Font”屬性也擁有一個編輯器：如果此屬性選擇了“...”按鈕，通過點(diǎn)擊此按鈕打開標(biāo)準(zhǔn)的 "font properties"對話框。

 “TfrxPropertyEditor”是所有屬性編輯器的基類，并在“frxDsgnIntf”中做了聲明：

TfrxPropertyEditor = class(TObject)
protected
procedure GetStrProc(const s: String);
function GetFloatValue: Extended;
function GetOrdValue: Integer;
function GetStrValue: String;
function GetVarValue: Variant;
procedure SetFloatValue(Value: Extended);
procedure SetOrdValue(Value: Integer);
procedure SetStrValue(const Value: String);
procedure SetVarValue(Value: Variant);
public
constructor Create(Designer: TfrxCustomDesigner); virtual;
destructor Destroy; override;
function Edit: Boolean; virtual;
function GetAttributes: TfrxPropertyAttributes; virtual;
function GetExtraLBSize: Integer; virtual;
function GetValue: String; virtual;
procedure GetValues; virtual;
procedure SetValue(const Value: String); virtual;
procedure OnDrawLBItem(Control: TWinControl; Index: Integer;
ARect: TRect; State: TOwnerDrawState); virtual;
procedure OnDrawItem(Canvas: TCanvas; ARect: TRect); virtual;
property Component: TPersistent readonly;
property frComponent: TfrxComponent readonly;
property Designer: TfrxCustomDesigner readonly;
property ItemHeight: Integer;
property PropInfo: PPropInfo readonly;
property Value: String;
property Values: TStrings readonly;
end;

你還可以從以下類中繼承，

TfrxIntegerProperty = class(TfrxPropertyEditor)
TfrxFloatProperty = class(TfrxPropertyEditor)
TfrxCharProperty = class(TfrxPropertyEditor)
TfrxStringProperty = class(TfrxPropertyEditor)
TfrxEnumProperty = class(TfrxPropertyEditor)
TfrxClassProperty = class(TfrxPropertyEditor)
TfrxComponentProperty = class(TfrxPropertyEditor)

多個屬性被定義在TfrxPropertyEditor類中：

Component：鏈接到父組件
frComponent：鏈接到父組件，但方便在某些情況下，轉(zhuǎn)換到TfrxComponent類型。
Designer：鏈接到報表設(shè)計器
ItemHeight：item高度
PropInfo：鏈接到PPropInfo結(jié)構(gòu)，該結(jié)構(gòu)包含了被編輯屬性的所有信息
Value：顯示為字符串的屬性值
Values：值列表；如果定義了“paValueList” 屬性，該屬性就用“GetValue”方法來填補(bǔ)。

下列系統(tǒng)方法可用于獲取或者設(shè)置所編輯的屬性值。

function GetFloatValue: Extended;
function GetOrdValue: Integer;
function GetStrValue: String;
function GetVarValue: Variant;
procedure SetFloatValue(Value: Extended);
procedure SetOrdValue(Value: Integer);
procedure SetStrValue(const Value: String);
procedure SetVarValue(Value: Variant);

你應(yīng)該選擇使用適合屬性類型的方法。如果屬性是屬于 “Integer” 類型，那么你就需要使用“GetOrdValue”和“SetOrdValue”方法。由于這些屬性包含了32-bit對象的地址，因此，這些方法也可用于“TObject" 類型的屬性，如MyFont := TFont(GetOrdValue)。

你可以從基類中繼承并重寫公共部分聲明的一些方法，從而創(chuàng)建你自己的編輯器。“GetAttributes”是其中一個需要被重寫的方法。通過以下方式定義其屬性：

TfrxPropertyAttribute = (paValueList, paSortList, paDialog, paMultiSelect,
paSubProperties, paReadOnly, paOwnerDraw);
TfrxPropertyAttributes = set of TfrxPropertyAttribute

屬性編輯器注冊由frxDsgnIntf 文件中定義的程序執(zhí)行：

procedure frxPropertyEditors.Register(PropertyType: PTypeInfo;
ComponentClass: TClass;
const PropertyName: String;
EditorClass:
TfrxPropertyEditorClass);

只有“PropertyType”參數(shù)需要進(jìn)行指定。 “ComponentClass” 和/或 “PropertyName”參數(shù)可能為空。

讓我們來看看三個屬性編輯器的例子。FastReport VCL報表要求Editor code 存放在與component code所在文件夾同名的文件夾中，其后綴名為'Editor'。

{ TFont property editor displays editor button('...') }
{ inherit from ClassProperty }
type
TfrxFontProperty = class(TfrxClassProperty)
public
function Edit: Boolean; override;
function GetAttributes: TfrxPropertyAttributes; override;
end;
function TfrxFontProperty.GetAttributes: TfrxPropertyAttributes;
begin
{ property has nested properties and editor;
it cannot be edited manually }
Result := [paMultiSelect, paDialog, paSubProperties, paReadOnly];
end;
function TfrxFontProperty.Edit: Boolean;
var
FontDialog: TFontDialog;
begin
{ create standard dialogue }
FontDialog := TFontDialog.Create(Application);
try
{ take property value }
FontDialog.Font := TFont(GetOrdValue);
FontDialog.Options := FontDialog.Options + [fdForceFontExist];
{ display dialogue }
Result := FontDialog.Execute;
{ bind new value }
if Result then
SetOrdValue(Integer(FontDialog.Font));
finally
FontDialog.Free;
end;
end;
{ registration }
frxPropertyEditors.Register(TypeInfo(TFont), nil, '', TfrxFontProperty);
--------------------------------------------------
{ TFont.Name property editor displays a drop-down list
of available fonts;
inherit from StringProperty, as property is of string type }
type
TfrxFontNameProperty = class(TfrxStringProperty)
public
function GetAttributes: TfrxPropertyAttributes; override;
procedure GetValues; override;
end;
function TfrxFontNameProperty.GetAttributes: TfrxPropertyAttributes;
begin
Result := [paMultiSelect, paValueList];
end;
procedure TfrxFontNameProperty.GetValues;
begin
Values.Assign(Screen.Fonts);
end;

{ registration }
frxPropertyEditors.Register(TypeInfo(String), TFont,
'Name', TfrxFontNameProperty);

-----------------------------------------
{ TPen.Style property editor displays a picture,
which is an example of the selected style }
type
TfrxPenStyleProperty = class(TfrxEnumProperty)
public
function GetAttributes: TfrxPropertyAttributes; override;
function GetExtraLBSize: Integer; override;
procedure OnDrawLBItem(Control: TWinControl; Index: Integer;
ARect: TRect; State: TOwnerDrawState); override;
procedure OnDrawItem(Canvas: TCanvas; ARect: TRect); override;
end;
function TfrxPenStyleProperty.GetAttributes: TfrxPropertyAttributes;
begin
Result := [paMultiSelect, paValueList, paOwnerDraw];
end;
{ method draws thick horizontal line with selected style }
procedure HLine(Canvas: TCanvas; X, Y, DX: Integer);
var
i: Integer;
begin
with Canvas do
begin
Pen.Color := clBlack;
for i := 0 to 1 do
begin
MoveTo(X, Y - 1 + i);
LineTo(X + DX, Y - 1 + i);
end;
end;
end;
{ drawing drop-down list }
procedure TfrxPenStyleProperty.OnDrawLBItem
(Control: TWinControl; Index: Integer;
ARect: TRect; State: TOwnerDrawState);
begin
with TListBox(Control), TListBox(Control).Canvas do
begin
FillRect(ARect);
TextOut(ARect.Left + 40, ARect.Top + 1, TListBox(Control).Items
[Index]);
Pen.Color := clGray;
Brush.Color := clWhite;
Rectangle(ARect.Left + 2, ARect.Top + 2,
ARect.Left + 36, ARect.Bottom - 2);
Pen.Style := TPenStyle(Index);
HLine(TListBox(Control).Canvas, ARect.Left + 3,
ARect.Top + (ARect.Bottom - ARect.Top) div 2, 32);
Pen.Style := psSolid;
end;
end;
{ drawing property value }
procedure TfrxPenStyleProperty.OnDrawItem(Canvas: TCanvas; ARect: TRect);
begin
with Canvas do
begin
TextOut(ARect.Left + 38, ARect.Top, Value);
Pen.Color := clGray;
Brush.Color := clWhite;
Rectangle(ARect.Left, ARect.Top + 1,
ARect.Left + 34, ARect.Bottom - 4);
Pen.Color := clBlack;
Pen.Style := TPenStyle(GetOrdValue);
HLine(Canvas, ARect.Left + 1,
ARect.Top + (ARect.Bottom - ARect.Top) div 2 - 1, 32);
Pen.Style := psSolid;
end;
end;
{ return picture width }
function TfrxPenStyleProperty.GetExtraLBSize: Integer;
begin
Result := 36;
end;
{ registration }
frxPropertyEditors.Register(TypeInfo(TPenStyle), TPen,
'Style', TfrxPenStyleProperty);