Writing Property Editors 编写属性编辑器
When you select a component in the designer its properties are displayed in the object inspector. You can create your own editor for any property. The “Font” property, for example, has an editor : if this property is selected a '...' button appears to the right of the line; open the standard "font properties" dialogue by clicking this button. Another example is the “Color” property. It opens the standard colors and color specimens names in a drop-down list.
“TfrxPropertyEditor” is the base class for all property editors and is declared in the “frxDsgnIntf” unit:
"TfrxPropertyEditor"是属性编辑器的基类，声明在frxDsgnIntf单元：
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;
You also can inherit from any of the following classes, which provide some basic functionality for working with a property of the corresponding type:
你还可以从下列任何类中继承，该类提供一些基本功能，用于与相应类型的属性工作：
TfrxIntegerProperty = class(TfrxPropertyEditor)
TfrxFloatProperty = class(TfrxPropertyEditor)
TfrxCharProperty = class(TfrxPropertyEditor)
TfrxStringProperty = class(TfrxPropertyEditor)
TfrxEnumProperty = class(TfrxPropertyEditor)
TfrxClassProperty = class(TfrxPropertyEditor)
TfrxComponentProperty = class(TfrxPropertyEditor)
Several properties are defined in the TfrxPropertyEditor class:
几个属性是在TfrxPropertyEditor 中类定义：
- Component link to parent component (not to property itself!) to which the given property belongs
- frComponent the same, but cast to TfrxComponent type (convenient in some cases)
- Designer link to the report designer
- ItemHeight item height, in which property is displayed; it can be useful in OnDrawXXX
- PropInfo link to PPropInfo structure, which contains information about the edited property
- Value property value displayed as a string // 属性的值显示为字符串
- Values list of values; this property is to be filled by the “GetValue” method, if the “paValueList” attribute is defined (see below)
The following are system methods. They can be used to get or set the edited property value.
定义的相关方法：
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);
You should use the methods appropriate to the property type. So, use “GetOrdValue” and “SetOrdValue” methods if the property is of “Integer” type, etc.. These methods are also used for working with properties of “TObject" type, since these properties contain a 32-bit object address. In these cases, just use a cast like: MyFont := TFont(GetOrdValue).
你应该使用属性类型相适应的方法。这些方法也适用于属性是“TObject”类型，因为这些属性包含一个32位对象地址，比如MyFont := TFont(GetOrdValue)，用类型转换进行处理。
To create your own editor, inherit from the base class and override some methods declared in the public section (which methods is dependent on the property type and functionality you wish to implement). One of the methods that will need to be overridden is “GetAttributes” which returns a set of property attributes. Attributes are defined in the following way:
编写自己的属性编辑器，要重写GetAttributes方法。返回一组属性值。属性值被定义如下方式：
TfrxPropertyAttribute = (paValueList, paSortList, paDialog, paMultiSelect,paSubProperties, paReadOnly, paOwnerDraw);
TfrxPropertyAttributes = set of TfrxPropertyAttribute;
Attribute meanings are:
属性值的意思：
- paValueList
property represents a drop-down list of values (for example the “Color” property);
if present then the “GetValues” method should be overridden
属性值是下拉列表形式，重写GetValues方法。
- paSortList
sorts list values; it is used together with paValueList
分类列表值；它与paValueList一起使用
- paDialog
property has an editor; if present a '...' button is displayed to the right of the line; Edit method is called by clicking on it
属性是个编辑器，调用Edit 方法。
- paMultiSelect
allows more than one object to be selected at the same time; some properties (such as “Name”, etc) do not have this attribute
- paSubProperties
property is object of TPersistent type and has its own properties, which should also be displayed (for example the “Font” property)
类似Font属性
- paReadOnly
value cannot be changed in the editor; some properties, of “Class” or “Set” types, have this attribute
只读的属性
- paOwnerDraw
property value is drawn by the “OnDrawItem” method; if the “paValueList” attribute is present then a drop-down list is drawn by the OnDrawLBItem method
自绘的属性，重写OnDrawItem方法.
The Edit method is called in two ways: either by selecting a property and double-clicking its value or (if property has paDialog attribute) by clicking the '...' button. This method should return “True” if property value was modified.
The “GetValue” method should return the property value as a string (it will be displayed in the object inspector). If you inherit from the TfrxPropertyEditor base class this method must be overridden.
The “SetValue” method is to set the property value, transferred as a string. If you inherit from the TfrxPropertyEditor base class this method must be overridden.
The “GetValues” method should be overridden if the “paValueList” attribute is set. This method should fill the “Values” property with values.
The following three methods allow manual drawing of the property value (the Color property editor works in the same way). These methods are called if the “paOwnerDraw” attribute is set.
以下3个方法手动绘制属性值。如果attribute 设置为paOwnerDraw.
The “OnDrawItem” method is called when the property value is drawn in the object inspector (when the property is not selected; otherwise its value is simply displayed in the editing line). For example, the Color property editor draws a rectangle to the left of property value, filled with the corresponding color.
The “GetExtraLBSize” method is called if the “paValueList” attribute is set. This method returns the number of pixels by which to adjust the “Drop-Down List” width to display the list. By default this method returns the value corresponding to the cell height. If you need to draw picture, with width larger than its height, the given method should be overridden.
The “OnDrawLBItem” method is called when drawing a string in a drop-down list if the paValueList attribute is set. This method is actually the TListBox.OnDrawItem event handler and has the same set of parameters.
Property editor registration is performed by the procedure defined in the frxDsgnIntf file:
属性编辑器的注册调用以下过程，声明在frxDsgnIntf 文件：
procedure frxPropertyEditors.Register(PropertyType: PTypeInfo;ComponentClass: TClass;const PropertyName: String;
EditorClass: TfrxPropertyEditorClass);
- PropertyType
information about the property type, returned by the “TypeInfo” system function, for example TypeInfo(String)
- ComponentClass
component name, with property you want to edit (may be nil)
- PropertyName
name of property you want to edit (may be a blank string)
- EditorClass
property editor name
Only the “PropertyType” parameter needs to be specified. The “ComponentClass” and/or “PropertyName” parameters may be blank. This allows the editor to be registered either to any property of PropertyType type, to any property of concrete ComponentClass components and its descendants, or to a PropertyName specific property of a specific component (or to any component if the ComponentClass parameter is blank).
参数PropertyType是必须的，其他可以不输入。
Let's look at three property editor examples. FastReport requires the Editor code to be placed in a file having the same name as the file having the component code, with 'Editor' suffixed to it.
举例：属性编辑器的代码文件用跟组件同样的文件名，加Editor做后缀存放。
--------------------------------------------------
{ TFont property editor displays editor button('...') } //字体属性编辑器
{ inherit from ClassProperty }
type
TfrxFontProperty = class(TfrxClassProperty)
public
//重写的方法
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 } //注册
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);
参考 frxADOEditor.pas 单元的使用。