Timer

The following two code samples illustrate how one could write an application that shows the current time.

User @lnxbil provides us with an example of a Modal whose text is changed in a goroutine to display the current time:

// Demo code for a timer based update
package main

import (
	"fmt"
	"time"

	"github.com/rivo/tview"
)

const refreshInterval = 500 * time.Millisecond

var (
	view *tview.Modal
	app  *tview.Application
)

func currentTimeString() string {
	t := time.Now()
	return fmt.Sprintf(t.Format("Current time is 15:04:05"))
}

func updateTime() {
	for {
		time.Sleep(refreshInterval)
		app.QueueUpdateDraw(func() {
			view.SetText(currentTimeString())
		})
	}
}

func main() {
	app = tview.NewApplication()
	view = tview.NewModal().
		SetText(currentTimeString()).
		AddButtons([]string{"Quit", "Cancel"}).
		SetDoneFunc(func(buttonIndex int, buttonLabel string) {
			if buttonLabel == "Quit" {
				app.Stop()
			}
		})

	go updateTime()
	if err := app.SetRoot(view, false).Run(); err != nil {
		panic(err)
	}
}

Similar in functionality but different in execution is the following example by @ardnew. Here, a screen refresh is triggered every 500 milliseconds and the current time is drawn in response to that screen refresh event. Calling Application.QueueUpdate() is not needed because Application.Draw() can be called from any goroutine. The example also shows how you may provide your own drawing routine.

// Demo code for a timer based update
package main

import (
	"time"

	"github.com/gdamore/tcell/v2"
	"github.com/rivo/tview"
)

const refreshInterval = 500 * time.Millisecond

var (
	view *tview.Box
	app  *tview.Application
)

func drawTime(screen tcell.Screen, x int, y int, width int, height int) (int, int, int, int) {
	timeStr := time.Now().Format("Current time is 15:04:05")
	tview.Print(screen, timeStr, x, height/2, width, tview.AlignCenter, tcell.ColorLime)
	return 0, 0, 0, 0
}

func refresh() {
	tick := time.NewTicker(refreshInterval)
	for {
		select {
		case <-tick.C:
			app.Draw()
		}
	}
}

func main() {
	app = tview.NewApplication()
	view = tview.NewBox().SetDrawFunc(drawTime)

	go refresh()
	if err := app.SetRoot(view, true).Run(); err != nil {
		panic(err)
	}
}