rui/view.go

package rui

import (
	"fmt"
	"strconv"
	"strings"
)

// Frame - the location and size of a rectangle area
type Frame struct {
	// Left - the left border
	Left float64
	// Top - the top border
	Top float64
	// Width - the width of a rectangle area
	Width float64
	// Height - the height of a rectangle area
	Height float64
}

// Right returns the right border
func (frame Frame) Right() float64 {
	return frame.Left + frame.Width
}

// Bottom returns the bottom border
func (frame Frame) Bottom() float64 {
	return frame.Top + frame.Height
}

// View - base view interface
type View interface {
	Properties
	fmt.Stringer
	ruiStringer

	// Init initializes fields of View by default values
	Init(session Session)
	// Session returns the current Session interface
	Session() Session
	// Parent returns the parent view
	Parent() View
	parentHTMLID() string
	setParentID(parentID string)
	// Tag returns the tag of View interface
	Tag() string
	// ID returns the id of the view
	ID() string
	// Focusable returns true if the view receives the focus
	Focusable() bool
	// Frame returns the location and size of the view in pixels
	Frame() Frame
	// Scroll returns the location size of the scrolable view in pixels
	Scroll() Frame
	// SetAnimated sets the value (second argument) of the property with name defined by the first argument.
	// Return "true" if the value has been set, in the opposite case "false" are returned and
	// a description of the error is written to the log
	SetAnimated(tag string, value interface{}, animation Animation) bool
	// SetChangeListener set the function to track the change of the View property
	SetChangeListener(tag string, listener func(View, string))

	handleCommand(self View, command string, data DataObject) bool
	htmlClass(disabled bool) string
	htmlTag() string
	closeHTMLTag() bool
	htmlID() string
	htmlSubviews(self View, buffer *strings.Builder)
	htmlProperties(self View, buffer *strings.Builder)
	htmlDisabledProperties(self View, buffer *strings.Builder)
	cssStyle(self View, builder cssBuilder)
	addToCSSStyle(addCSS map[string]string)

	getTransitions() Params

	onResize(self View, x, y, width, height float64)
	onItemResize(self View, index int, x, y, width, height float64)
	setNoResizeEvent()
	isNoResizeEvent() bool
	setScroll(x, y, width, height float64)
}

// viewData - base implementation of View interface
type viewData struct {
	viewStyle
	session          Session
	tag              string
	viewID           string
	_htmlID          string
	parentID         string
	systemClass      string
	changeListener   map[string]func(View, string)
	singleTransition map[string]Animation
	addCSS           map[string]string
	frame            Frame
	scroll           Frame
	noResizeEvent    bool
	created          bool
	//animation map[string]AnimationEndListener
}

func newView(session Session) View {
	view := new(viewData)
	view.Init(session)
	return view
}

func setInitParams(view View, params Params) {
	if params != nil {
		session := view.Session()
		if !session.ignoreViewUpdates() {
			session.setIgnoreViewUpdates(true)
			defer session.setIgnoreViewUpdates(false)
		}
		for _, tag := range params.AllTags() {
			if value, ok := params[tag]; ok {
				view.Set(tag, value)
			}
		}
	}
}

// NewView create new View object and return it
func NewView(session Session, params Params) View {
	view := new(viewData)
	view.Init(session)
	setInitParams(view, params)
	return view
}

func (view *viewData) Init(session Session) {
	view.viewStyle.init()
	view.tag = "View"
	view.session = session
	view.changeListener = map[string]func(View, string){}
	view.addCSS = map[string]string{}
	//view.animation = map[string]AnimationEndListener{}
	view.singleTransition = map[string]Animation{}
	view.noResizeEvent = false
	view.created = false
}

func (view *viewData) Session() Session {
	return view.session
}

func (view *viewData) Parent() View {
	return view.session.viewByHTMLID(view.parentID)
}

func (view *viewData) parentHTMLID() string {
	return view.parentID
}

func (view *viewData) setParentID(parentID string) {
	view.parentID = parentID
}

func (view *viewData) Tag() string {
	return view.tag
}

func (view *viewData) ID() string {
	return view.viewID
}

func (view *viewData) ViewByID(id string) View {
	if id == view.ID() {
		if v := view.session.viewByHTMLID(view.htmlID()); v != nil {
			return v
		}
		return view
	}
	return nil
}

func (view *viewData) Focusable() bool {
	return false
}

func (view *viewData) Remove(tag string) {
	view.remove(strings.ToLower(tag))
}

func (view *viewData) remove(tag string) {
	switch tag {
	case ID:
		view.viewID = ""

	case Style, StyleDisabled:
		if _, ok := view.properties[tag]; ok {
			delete(view.properties, tag)
			updateProperty(view.htmlID(), "class", view.htmlClass(IsDisabled(view, "")), view.session)
		}

	case FocusEvent, LostFocusEvent:
		view.removeFocusListener(tag)

	case KeyDownEvent, KeyUpEvent:
		view.removeKeyListener(tag)

	case ClickEvent, DoubleClickEvent, MouseDown, MouseUp, MouseMove, MouseOut, MouseOver, ContextMenuEvent:
		view.removeMouseListener(tag)

	case PointerDown, PointerUp, PointerMove, PointerOut, PointerOver, PointerCancel:
		view.removePointerListener(tag)

	case TouchStart, TouchEnd, TouchMove, TouchCancel:
		view.removeTouchListener(tag)

	case TransitionRunEvent, TransitionStartEvent, TransitionEndEvent, TransitionCancelEvent:
		view.removeTransitionListener(tag)

	case AnimationStartEvent, AnimationEndEvent, AnimationIterationEvent, AnimationCancelEvent:
		view.removeAnimationListener(tag)

	case ResizeEvent, ScrollEvent:
		delete(view.properties, tag)

	case Content:
		if _, ok := view.properties[Content]; ok {
			delete(view.properties, Content)
			updateInnerHTML(view.htmlID(), view.session)
		}

	default:
		view.viewStyle.remove(tag)
		viewPropertyChanged(view, tag)
	}

	view.propertyChangedEvent(tag)
}

func (view *viewData) propertyChangedEvent(tag string) {
	if listener, ok := view.changeListener[tag]; ok {
		listener(view, tag)
	}

	switch tag {
	case BorderLeft, BorderRight, BorderTop, BorderBottom,
		BorderStyle, BorderLeftStyle, BorderRightStyle, BorderTopStyle, BorderBottomStyle,
		BorderColor, BorderLeftColor, BorderRightColor, BorderTopColor, BorderBottomColor,
		BorderWidth, BorderLeftWidth, BorderRightWidth, BorderTopWidth, BorderBottomWidth:
		tag = Border

	case CellBorderStyle, CellBorderColor, CellBorderWidth,
		CellBorderLeft, CellBorderLeftStyle, CellBorderLeftColor, CellBorderLeftWidth,
		CellBorderRight, CellBorderRightStyle, CellBorderRightColor, CellBorderRightWidth,
		CellBorderTop, CellBorderTopStyle, CellBorderTopColor, CellBorderTopWidth,
		CellBorderBottom, CellBorderBottomStyle, CellBorderBottomColor, CellBorderBottomWidth:
		tag = CellBorder

	case OutlineColor, OutlineStyle, OutlineWidth:
		tag = Outline

	case RadiusX, RadiusY, RadiusTopLeft, RadiusTopLeftX, RadiusTopLeftY,
		RadiusTopRight, RadiusTopRightX, RadiusTopRightY,
		RadiusBottomLeft, RadiusBottomLeftX, RadiusBottomLeftY,
		RadiusBottomRight, RadiusBottomRightX, RadiusBottomRightY:
		tag = Radius

	case MarginTop, MarginRight, MarginBottom, MarginLeft,
		"top-margin", "right-margin", "bottom-margin", "left-margin":
		tag = Margin

	case PaddingTop, PaddingRight, PaddingBottom, PaddingLeft,
		"top-padding", "right-padding", "bottom-padding", "left-padding":
		tag = Padding

	case CellPaddingTop, CellPaddingRight, CellPaddingBottom, CellPaddingLeft:
		tag = CellPadding

	case ColumnSeparatorStyle, ColumnSeparatorWidth, ColumnSeparatorColor:
		tag = ColumnSeparator

	default:
		return
	}

	if listener, ok := view.changeListener[tag]; ok {
		listener(view, tag)
	}

}

func (view *viewData) Set(tag string, value interface{}) bool {
	return view.set(strings.ToLower(tag), value)
}

func (view *viewData) set(tag string, value interface{}) bool {
	if value == nil {
		view.remove(tag)
		return true
	}

	result := func(res bool) bool {
		if res {
			view.propertyChangedEvent(tag)
		}
		return res
	}

	switch tag {
	case ID:
		text, ok := value.(string)
		if !ok {
			notCompatibleType(ID, value)
			return false
		}
		view.viewID = text

	case Style, StyleDisabled:
		text, ok := value.(string)
		if !ok {
			notCompatibleType(ID, value)
			return false
		}
		view.properties[tag] = text
		if view.created {
			updateProperty(view.htmlID(), "class", view.htmlClass(IsDisabled(view, "")), view.session)
		}

	case FocusEvent, LostFocusEvent:
		return result(view.setFocusListener(tag, value))

	case KeyDownEvent, KeyUpEvent:
		return result(view.setKeyListener(tag, value))

	case ClickEvent, DoubleClickEvent, MouseDown, MouseUp, MouseMove, MouseOut, MouseOver, ContextMenuEvent:
		return result(view.setMouseListener(tag, value))

	case PointerDown, PointerUp, PointerMove, PointerOut, PointerOver, PointerCancel:
		return result(view.setPointerListener(tag, value))

	case TouchStart, TouchEnd, TouchMove, TouchCancel:
		return result(view.setTouchListener(tag, value))

	case TransitionRunEvent, TransitionStartEvent, TransitionEndEvent, TransitionCancelEvent:
		return result(view.setTransitionListener(tag, value))

	case AnimationStartEvent, AnimationEndEvent, AnimationIterationEvent, AnimationCancelEvent:
		return result(view.setAnimationListener(tag, value))

	case ResizeEvent, ScrollEvent:
		return result(view.setFrameListener(tag, value))

	default:
		if !view.viewStyle.set(tag, value) {
			return false
		}
		if view.created {
			viewPropertyChanged(view, tag)
		}
	}

	view.propertyChangedEvent(tag)
	return true
}

func viewPropertyChanged(view *viewData, tag string) {
	if view.updateTransformProperty(tag) {
		return
	}

	htmlID := view.htmlID()
	session := view.session

	switch tag {
	case Disabled:
		updateInnerHTML(view.parentHTMLID(), session)

	case Background:
		updateCSSProperty(htmlID, Background, view.backgroundCSS(session), session)
		return

	case Border:
		if getBorder(view, Border) == nil {
			updateCSSProperty(htmlID, BorderWidth, "", session)
			updateCSSProperty(htmlID, BorderColor, "", session)
			updateCSSProperty(htmlID, BorderStyle, "none", session)
			return
		}
		fallthrough

	case BorderLeft, BorderRight, BorderTop, BorderBottom:
		if border := getBorder(view, Border); border != nil {
			updateCSSProperty(htmlID, BorderWidth, border.cssWidthValue(session), session)
			updateCSSProperty(htmlID, BorderColor, border.cssColorValue(session), session)
			updateCSSProperty(htmlID, BorderStyle, border.cssStyleValue(session), session)
		}
		return

	case BorderStyle, BorderLeftStyle, BorderRightStyle, BorderTopStyle, BorderBottomStyle:
		if border := getBorder(view, Border); border != nil {
			updateCSSProperty(htmlID, BorderStyle, border.cssStyleValue(session), session)
		}
		return

	case BorderColor, BorderLeftColor, BorderRightColor, BorderTopColor, BorderBottomColor:
		if border := getBorder(view, Border); border != nil {
			updateCSSProperty(htmlID, BorderColor, border.cssColorValue(session), session)
		}
		return

	case BorderWidth, BorderLeftWidth, BorderRightWidth, BorderTopWidth, BorderBottomWidth:
		if border := getBorder(view, Border); border != nil {
			updateCSSProperty(htmlID, BorderWidth, border.cssWidthValue(session), session)
		}
		return

	case Outline, OutlineColor, OutlineStyle, OutlineWidth:
		updateCSSProperty(htmlID, Outline, GetOutline(view, "").cssString(), session)
		return

	case Shadow:
		updateCSSProperty(htmlID, "box-shadow", shadowCSS(view, Shadow, session), session)
		return

	case TextShadow:
		updateCSSProperty(htmlID, "text-shadow", shadowCSS(view, TextShadow, session), session)
		return

	case Radius, RadiusX, RadiusY, RadiusTopLeft, RadiusTopLeftX, RadiusTopLeftY,
		RadiusTopRight, RadiusTopRightX, RadiusTopRightY,
		RadiusBottomLeft, RadiusBottomLeftX, RadiusBottomLeftY,
		RadiusBottomRight, RadiusBottomRightX, RadiusBottomRightY:
		radius := GetRadius(view, "")
		updateCSSProperty(htmlID, "border-radius", radius.cssString(), session)
		return

	case Margin, MarginTop, MarginRight, MarginBottom, MarginLeft,
		"top-margin", "right-margin", "bottom-margin", "left-margin":
		margin := GetMargin(view, "")
		updateCSSProperty(htmlID, Margin, margin.cssString(), session)
		return

	case Padding, PaddingTop, PaddingRight, PaddingBottom, PaddingLeft,
		"top-padding", "right-padding", "bottom-padding", "left-padding":
		padding := GetPadding(view, "")
		updateCSSProperty(htmlID, Padding, padding.cssString(), session)
		return

	case AvoidBreak:
		if avoid, ok := boolProperty(view, AvoidBreak, session); ok {
			if avoid {
				updateCSSProperty(htmlID, "break-inside", "avoid", session)
			} else {
				updateCSSProperty(htmlID, "break-inside", "auto", session)
			}
		}
		return

	case Clip:
		if clip := getClipShape(view, Clip, session); clip != nil && clip.valid(session) {
			updateCSSProperty(htmlID, `clip-path`, clip.cssStyle(session), session)
		} else {
			updateCSSProperty(htmlID, `clip-path`, "none", session)
		}
		return

	case ShapeOutside:
		if clip := getClipShape(view, ShapeOutside, session); clip != nil && clip.valid(session) {
			updateCSSProperty(htmlID, ShapeOutside, clip.cssStyle(session), session)
		} else {
			updateCSSProperty(htmlID, ShapeOutside, "none", session)
		}
		return

	case Filter:
		text := ""
		if value := view.getRaw(Filter); value != nil {
			if filter, ok := value.(ViewFilter); ok {
				text = filter.cssStyle(session)
			}
		}
		updateCSSProperty(htmlID, Filter, text, session)
		return

	case FontName:
		if font, ok := stringProperty(view, FontName, session); ok {
			updateCSSProperty(htmlID, "font-family", font, session)
		} else {
			updateCSSProperty(htmlID, "font-family", "", session)
		}
		return

	case Italic:
		if state, ok := boolProperty(view, tag, session); ok {
			if state {
				updateCSSProperty(htmlID, "font-style", "italic", session)
			} else {
				updateCSSProperty(htmlID, "font-style", "normal", session)
			}
		} else {
			updateCSSProperty(htmlID, "font-style", "", session)
		}
		return

	case SmallCaps:
		if state, ok := boolProperty(view, tag, session); ok {
			if state {
				updateCSSProperty(htmlID, "font-variant", "small-caps", session)
			} else {
				updateCSSProperty(htmlID, "font-variant", "normal", session)
			}
		} else {
			updateCSSProperty(htmlID, "font-variant", "", session)
		}
		return

	case Strikethrough, Overline, Underline:
		updateCSSProperty(htmlID, "text-decoration", view.cssTextDecoration(session), session)
		for _, tag2 := range []string{TextLineColor, TextLineStyle, TextLineThickness} {
			viewPropertyChanged(view, tag2)
		}
		return

	case Transition:
		view.updateTransitionCSS()
		return

	case AnimationTag:
		updateCSSProperty(htmlID, AnimationTag, view.animationCSS(session), session)
		return

	case AnimationPaused:
		paused, ok := boolProperty(view, AnimationPaused, session)
		if !ok {
			updateCSSProperty(htmlID, `animation-play-state`, ``, session)
		} else if paused {
			updateCSSProperty(htmlID, `animation-play-state`, `paused`, session)
		} else {
			updateCSSProperty(htmlID, `animation-play-state`, `running`, session)
		}
		return
	}

	if cssTag, ok := sizeProperties[tag]; ok {
		size, _ := sizeProperty(view, tag, session)
		updateCSSProperty(htmlID, cssTag, size.cssString(""), session)
		return
	}

	colorTags := map[string]string{
		BackgroundColor: BackgroundColor,
		TextColor:       "color",
		TextLineColor:   "text-decoration-color",
	}
	if cssTag, ok := colorTags[tag]; ok {
		if color, ok := colorProperty(view, tag, session); ok {
			updateCSSProperty(htmlID, cssTag, color.cssString(), session)
		} else {
			updateCSSProperty(htmlID, cssTag, "", session)
		}
		return
	}

	if valuesData, ok := enumProperties[tag]; ok && valuesData.cssTag != "" {
		n, _ := enumProperty(view, tag, session, 0)
		updateCSSProperty(htmlID, valuesData.cssTag, valuesData.cssValues[n], session)
		return
	}

	for _, floatTag := range []string{ScaleX, ScaleY, ScaleZ, RotateX, RotateY, RotateZ} {
		if tag == floatTag {
			if f, ok := floatProperty(view, floatTag, session, 0); ok {
				updateCSSProperty(htmlID, floatTag, strconv.FormatFloat(f, 'g', -1, 64), session)
			}
			return
		}
	}
}

func (view *viewData) Get(tag string) interface{} {
	return view.get(strings.ToLower(tag))
}

func (view *viewData) get(tag string) interface{} {
	return view.viewStyle.get(tag)
}

func (view *viewData) htmlTag() string {
	if semantics := GetSemantics(view, ""); semantics > DefaultSemantics {
		values := enumProperties[Semantics].cssValues
		if semantics < len(values) {
			return values[semantics]
		}
	}
	return "div"
}

func (view *viewData) closeHTMLTag() bool {
	return true
}

func (view *viewData) htmlID() string {
	if view._htmlID == "" {
		view._htmlID = view.session.nextViewID()
	}
	return view._htmlID
}

func (view *viewData) htmlSubviews(self View, buffer *strings.Builder) {
}

func (view *viewData) addToCSSStyle(addCSS map[string]string) {
	view.addCSS = addCSS
}

func (view *viewData) cssStyle(self View, builder cssBuilder) {
	view.viewStyle.cssViewStyle(builder, view.session)
	switch GetVisibility(view, "") {
	case Invisible:
		builder.add(`visibility`, `hidden`)

	case Gone:
		builder.add(`display`, `none`)
	}

	if view.addCSS != nil {
		for tag, value := range view.addCSS {
			builder.add(tag, value)
		}
	}
}

func (view *viewData) htmlProperties(self View, buffer *strings.Builder) {
	view.created = true
	if view.frame.Left != 0 || view.frame.Top != 0 || view.frame.Width != 0 || view.frame.Height != 0 {
		buffer.WriteString(fmt.Sprintf(` data-left="%g" data-top="%g" data-width="%g" data-height="%g"`,
			view.frame.Left, view.frame.Top, view.frame.Width, view.frame.Height))
	}
}

func (view *viewData) htmlDisabledProperties(self View, buffer *strings.Builder) {
	if IsDisabled(self, "") {
		buffer.WriteString(` data-disabled="1"`)
	} else {
		buffer.WriteString(` data-disabled="0"`)
	}
}

func viewHTML(view View, buffer *strings.Builder) {
	viewHTMLTag := view.htmlTag()
	buffer.WriteRune('<')
	buffer.WriteString(viewHTMLTag)
	buffer.WriteString(` id="`)
	buffer.WriteString(view.htmlID())
	buffer.WriteRune('"')

	disabled := IsDisabled(view, "")

	if cls := view.htmlClass(disabled); cls != "" {
		buffer.WriteString(` class="`)
		buffer.WriteString(cls)
		buffer.WriteRune('"')
	}

	var cssBuilder viewCSSBuilder
	view.cssStyle(view, &cssBuilder)

	if style := cssBuilder.finish(); style != "" {
		buffer.WriteString(` style="`)
		buffer.WriteString(style)
		buffer.WriteRune('"')
	}

	buffer.WriteRune(' ')
	view.htmlProperties(view, buffer)
	buffer.WriteRune(' ')
	view.htmlDisabledProperties(view, buffer)

	if view.isNoResizeEvent() {
		buffer.WriteString(` data-noresize="1" `)
	} else {
		buffer.WriteRune(' ')
	}

	if view.Focusable() && !disabled {
		buffer.WriteString(`tabindex="0" `)
	}

	buffer.WriteString(`onscroll="scrollEvent(this, event)" `)

	keyEventsHtml(view, buffer)
	mouseEventsHtml(view, buffer)
	pointerEventsHtml(view, buffer)
	touchEventsHtml(view, buffer)
	focusEventsHtml(view, buffer)
	transitionEventsHtml(view, buffer)
	animationEventsHtml(view, buffer)

	buffer.WriteRune('>')
	view.htmlSubviews(view, buffer)
	if view.closeHTMLTag() {
		buffer.WriteString(`</`)
		buffer.WriteString(viewHTMLTag)
		buffer.WriteRune('>')
	}
}

func (view *viewData) htmlClass(disabled bool) string {
	cls := "ruiView"
	disabledStyle := false
	if disabled {
		if value, ok := stringProperty(view, StyleDisabled, view.Session()); ok && value != "" {
			cls += " " + value
			disabledStyle = true
		}
	}
	if !disabledStyle {
		if value, ok := stringProperty(view, Style, view.Session()); ok {
			cls += " " + value
		}
	}

	if view.systemClass != "" {
		cls = view.systemClass + " " + cls
	}

	return cls
}

func (view *viewData) handleCommand(self View, command string, data DataObject) bool {
	switch command {

	case KeyDownEvent, KeyUpEvent:
		if !IsDisabled(self, "") {
			handleKeyEvents(self, command, data)
		}

	case ClickEvent, DoubleClickEvent, MouseDown, MouseUp, MouseMove, MouseOut, MouseOver, ContextMenuEvent:
		handleMouseEvents(self, command, data)

	case PointerDown, PointerUp, PointerMove, PointerOut, PointerOver, PointerCancel:
		handlePointerEvents(self, command, data)

	case TouchStart, TouchEnd, TouchMove, TouchCancel:
		handleTouchEvents(self, command, data)

	case FocusEvent, LostFocusEvent:
		for _, listener := range getFocusListeners(view, "", command) {
			listener(self)
		}

	case TransitionRunEvent, TransitionStartEvent, TransitionEndEvent, TransitionCancelEvent:
		view.handleTransitionEvents(command, data)

	case AnimationStartEvent, AnimationEndEvent, AnimationIterationEvent, AnimationCancelEvent:
		view.handleAnimationEvents(command, data)

	case "scroll":
		view.onScroll(view, dataFloatProperty(data, "x"), dataFloatProperty(data, "y"), dataFloatProperty(data, "width"), dataFloatProperty(data, "height"))

	case "widthChanged":
		if value, ok := data.PropertyValue("width"); ok {
			if width, ok := StringToSizeUnit(value); ok {
				self.setRaw(Width, width)
			}
		}

	case "heightChanged":
		if value, ok := data.PropertyValue("height"); ok {
			if height, ok := StringToSizeUnit(value); ok {
				self.setRaw(Height, height)
			}
		}

		/*
			case "resize":
				floatProperty := func(tag string) float64 {
					if value, ok := data.PropertyValue(tag); ok {
						if result, err := strconv.ParseFloat(value, 64); err == nil {
							return result
						}
					}
					return 0
				}

				self.onResize(self, floatProperty("x"), floatProperty("y"), floatProperty("width"), floatProperty("height"))
				return true
		*/
	default:
		return false
	}
	return true

}

func ruiViewString(view View, viewTag string, writer ruiWriter) {
	writer.startObject(viewTag)

	tags := view.AllTags()
	count := len(tags)
	if count > 0 {
		if count > 1 {
			tagToStart := func(tag string) {
				for i, t := range tags {
					if t == tag {
						if i > 0 {
							for n := i; n > 0; n-- {
								tags[n] = tags[n-1]
							}
							tags[0] = tag
						}
						return
					}
				}
			}
			tagToStart(StyleDisabled)
			tagToStart(Style)
			tagToStart(ID)
		}

		for _, tag := range tags {
			if value := view.Get(tag); value != nil {
				writer.writeProperty(tag, value)
			}
		}
	}

	writer.endObject()
}

func (view *viewData) ruiString(writer ruiWriter) {
	ruiViewString(view, view.Tag(), writer)
}

func (view *viewData) String() string {
	writer := newRUIWriter()
	view.ruiString(writer)
	return writer.finish()
}

func (view *viewData) SetChangeListener(tag string, listener func(View, string)) {
	if listener == nil {
		delete(view.changeListener, tag)
	} else {
		view.changeListener[tag] = listener
	}
}