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package main
import (
"image/color"
"log"
"os"
"strconv"
"gioui.org/app" // app contains Window handling.
"gioui.org/font/gofont" // gofont is used for loading the default font.
"gioui.org/io/key" // key is used for keyboard events.
"gioui.org/io/system" // system is used for system events (e.g. closing the window).
"gioui.org/layout" // layout is used for layouting widgets.
"gioui.org/op" // op is used for recording different operations.
"gioui.org/unit" // unit is used to define pixel-independent sizes
"gioui.org/widget" // widget contains state handling for widgets.
"gioui.org/widget/material" // material contains material design widgets.
)
func main() {
// The ui loop is separated from the application window creation
// such that it can be used for testing.
ui := NewUI()
// This creates a new application window and starts the UI.
go func() {
w := app.NewWindow(
app.Title("Temperature Converter"),
app.Size(unit.Dp(360), unit.Dp(47)),
)
if err := ui.Run(w); err != nil {
log.Println(err)
os.Exit(1)
}
os.Exit(0)
}()
// This starts Gio main.
app.Main()
}
// defaultMargin is a margin applied in multiple places to give
// widgets room to breathe.
var defaultMargin = unit.Dp(10)
// UI holds all of the application state.
type UI struct {
// Theme is used to hold the fonts used throughout the application.
Theme *material.Theme
// Converter displays and modifies the state.
Converter Converter
}
// NewUI creates a new UI using the Go Fonts.
func NewUI() *UI {
ui := &UI{}
ui.Theme = material.NewTheme(gofont.Collection())
ui.Converter.Init()
return ui
}
// Run handles window events and renders the application.
func (ui *UI) Run(w *app.Window) error {
var ops op.Ops
// listen for events happening on the window.
for e := range w.Events() {
// detect the type of the event.
switch e := e.(type) {
// this is sent when the application should re-render.
case system.FrameEvent:
// gtx is used to pass around rendering and event information.
gtx := layout.NewContext(&ops, e)
// render and handle UI.
ui.Layout(gtx)
// render and handle the operations from the UI.
e.Frame(gtx.Ops)
// handle a global key press.
case key.Event:
switch e.Name {
// when we click escape, let's close the window.
case key.NameEscape:
return nil
}
// this is sent when the application is closed.
case system.DestroyEvent:
return e.Err
}
}
return nil
}
// Layout displays the main program layout.
func (ui *UI) Layout(gtx layout.Context) layout.Dimensions {
// inset is used to add padding around the window border.
inset := layout.UniformInset(defaultMargin)
return inset.Layout(gtx, func(gtx layout.Context) layout.Dimensions {
return ui.Converter.Layout(ui.Theme, gtx)
})
}
// Converter is a component that keeps track of it's state and
// displays itself as two editors.
type Converter struct {
Celsius Field
Fahrenheit Field
}
// Init is used to set the inital state.
func (conv *Converter) Init() {
conv.Celsius.SingleLine = true
conv.Fahrenheit.SingleLine = true
}
// Layout lays out the editors.
func (conv *Converter) Layout(th *material.Theme, gtx layout.Context) layout.Dimensions {
// We use an empty widget to add spacing between widgets.
spacer := layout.Rigid(layout.Spacer{Width: defaultMargin}.Layout)
// check whether the celsius value has changed.
if conv.Celsius.Changed() {
// try to convert the value to an integer
newValue, err := strconv.Atoi(conv.Celsius.Text())
// update whether the editor is displaying a valid value
conv.Celsius.Invalid = err != nil
if !conv.Celsius.Invalid {
// update the other editor when it's valid
conv.Fahrenheit.Invalid = false
conv.Fahrenheit.SetText(strconv.Itoa(newValue*9/5 + 32))
}
}
// check whether the fahrenheit value has changed.
if conv.Fahrenheit.Changed() {
newValue, err := strconv.Atoi(conv.Fahrenheit.Text())
conv.Fahrenheit.Invalid = err != nil
if !conv.Fahrenheit.Invalid {
conv.Celsius.Invalid = false
conv.Celsius.SetText(strconv.Itoa((newValue - 32) * 5 / 9))
}
}
// TODO: use proper baseline alignment.
return layout.Flex{}.Layout(gtx,
layout.Flexed(1, func(gtx layout.Context) layout.Dimensions {
return conv.Celsius.Layout(th, gtx)
}),
spacer,
layout.Rigid(material.Body1(th, "Celsius").Layout),
spacer,
layout.Rigid(material.Body1(th, "=").Layout),
spacer,
layout.Flexed(1, func(gtx layout.Context) layout.Dimensions {
return conv.Fahrenheit.Layout(th, gtx)
}),
spacer,
layout.Rigid(material.Body1(th, "Fahrenheit").Layout),
)
}
// Field implements an editor that allows updating the state and detect
// changes to the field from other sources.
type Field struct {
widget.Editor
Invalid bool
old string
}
// Changed checks once whether the editor context has changed.
func (ed *Field) Changed() bool {
newText := ed.Editor.Text()
changed := newText != ed.old
ed.old = newText
return changed
}
// SetText sets editor content without marking the editor changed.
func (ed *Field) SetText(s string) {
ed.old = s
ed.Editor.SetText(s)
}
// Layout handles the editor with the appropriate color and border.
func (ed *Field) Layout(th *material.Theme, gtx layout.Context) layout.Dimensions {
// Determine colors based on the state of the editor.
borderWidth := float32(0.5)
borderColor := color.NRGBA{A: 107}
switch {
case ed.Editor.Focused():
borderColor = th.Palette.ContrastBg
borderWidth = 2
case ed.Invalid:
borderColor = color.NRGBA{R: 200, A: 0xFF}
}
// draw an editor with a border.
return widget.Border{
Color: borderColor,
CornerRadius: unit.Dp(4),
Width: unit.Dp(borderWidth),
}.Layout(gtx, func(gtx layout.Context) layout.Dimensions {
return layout.UniformInset(unit.Dp(4)).Layout(gtx,
material.Editor(th, &ed.Editor, "").Layout)
})
}