rocket9labs.com/content/post/tview-and-you.md

---
title: "tview and you - Creating Rich Terminal User Interfaces"
date: 2019-11-08T01:42:18-07:00
categories: [tutorial]
---

[![Recording of presentation demo](https://raw.githubusercontent.com/rivo/tview/master/tview.gif)](https://github.com/rivo/tview/tree/master/demos/presentation)

This is an introduction to using [tview](https://github.com/rivo/tview) (or [cview](https://gitlab.com/tslocum/cview)) to create rich terminal-based user interfaces with [Go](https://golang.org).

## Primitives

The [Primitive](https://godoc.org/github.com/rivo/tview#Primitive) interface is as follows:

{{< highlight go >}}
type Primitive interface {
	Draw(screen tcell.Screen)
	GetRect() (int, int, int, int)
	SetRect(x, y, width, height int)
	InputHandler() func(event *tcell.EventKey, setFocus func(p Primitive))
	Focus(delegate func(p Primitive))
	Blur()
	GetFocusable() Focusable
}
{{< / highlight >}}

[Box](https://godoc.org/github.com/rivo/tview#Box) is the only primitive implemented.
It has a size, padding amount, optional border, optional title and background color.

## Widgets

Widgets are structs which embed a [Box](https://godoc.org/github.com/rivo/tview#Box) and build upon it.

From the [TextView](https://godoc.org/github.com/rivo/tview#TextView) declaration:

{{< highlight go >}}
type TextView struct {
	*Box

	// The text buffer.
	buffer []string

	// The text alignment, one of AlignLeft, AlignCenter, or AlignRight.
	align int

	// ...
}
{{< / highlight >}}

Some widgets allow nesting other widgets within them, such as [Grid](https://godoc.org/github.com/rivo/tview#Grid).

Most widget commands may be chained together:

{{< highlight go >}}
nameLabel := tview.NewTextView().
	SetTextAlign(tview.AlignRight).
	SetDynamicColors(true).
	SetWrap(true).
	SetWordWrap(true).
	SetText("Please enter your name:")
{{< / highlight >}}

New widgets may be defined, as documented in the [Primitive demo](https://github.com/rivo/tview/tree/master/demos/primitive).

### Widget Elements

---

[**Button**](https://godoc.org/github.com/rivo/tview#Button) is a labeled box that triggers an action when selected.

{{< highlight go >}}
button := tview.NewButton("OK").SetSelectedFunc(func() {
	pressedOK()
})
{{< / highlight >}}

---

[**Checkbox**](https://godoc.org/github.com/rivo/tview#Checkbox) holds a label and boolean value which may be checked and unchecked.

{{< highlight go >}}
checkbox := tview.NewCheckbox().SetLabel("Toggle value with Enter: ")
{{< / highlight >}}

---

[**DropDown**](https://godoc.org/github.com/rivo/tview#DropDown) holds one or more options which may be selected as a dropdown list.

{{< highlight go >}}
dropdown := tview.NewDropDown().
	SetLabel("Select an option with Enter: ").
	SetOptions([]string{"Foo", "Bar", "Baz"}, nil)
{{< / highlight >}}

---

[**InputField**](https://godoc.org/github.com/rivo/tview#InputField) is a box where text may be entered.

{{< highlight go >}}
inputField := tview.NewInputField().
	SetLabel("Name: ").
	SetPlaceholder("John Smith").
	SetFieldWidth(14).
	SetDoneFunc(func(key tcell.Key) {
		processName()
	})
{{< / highlight >}}

---

[**Modal**](https://godoc.org/github.com/rivo/tview#Modal) is a centered message window which may have one or more buttons.

{{< highlight go >}}
modal := tview.NewModal().
	SetText("Are you sure you want to exit?").
	AddButtons([]string{"Cancel", "Quit"}).
	SetDoneFunc(func(buttonIndex int, buttonLabel string) {
		if buttonIndex == 1 {
			app.Stop()
		}
	})
{{< / highlight >}}

---

[**TextView**](https://godoc.org/github.com/rivo/tview#TextView) is a box containing text.
[Colored text](https://godoc.org/github.com/rivo/tview#hdr-Colors) is supported when enabled.

{{< highlight go >}}
textView := tview.NewTextView().
	SetWrap(true).
	SetWordWrap(true).
	SetText("Hello, World!")
{{< / highlight >}}

---

### Widget Containers

---

[**Flex**](https://godoc.org/github.com/rivo/tview#Flex) is a [flexbox layout](https://en.wikipedia.org/wiki/CSS_Flexible_Box_Layout) container.

See the [Flex demo](https://github.com/rivo/tview/tree/master/demos/flex) for example usage.

---

[**Grid**](https://godoc.org/github.com/rivo/tview#Grid) is a [grid layout](https://en.wikipedia.org/wiki/CSS_grid_layout) container.

See the [Grid demo](https://github.com/rivo/tview/tree/master/demos/grid) for example usage.

---

[**Form**](https://godoc.org/github.com/rivo/tview#Form) displays one or more form elements in a vertical or horizontal layout.

See the [Form demo](https://github.com/rivo/tview/tree/master/demos/form) for example usage.

---

[**List**](https://godoc.org/github.com/rivo/tview#List) displays one or more widgets as a selectable list.

See the [List demo](https://github.com/rivo/tview/tree/master/demos/list) for example usage.

---

[**Pages**](https://godoc.org/github.com/rivo/tview#Pages) displays one or more widgets at a time.

See the [Pages demo](https://github.com/rivo/tview/tree/master/demos/pages) for example usage.

---

[**Table**](https://godoc.org/github.com/rivo/tview#Table) displays one or more widgets in rows and columns.

See the [Table demo](https://github.com/rivo/tview/tree/master/demos/table) for example usage.

---

[**TreeView**](https://godoc.org/github.com/rivo/tview#TreeView) displays one or more widgets in a tree.

See the [TreeView demo](https://github.com/rivo/tview/tree/master/demos/treeview) for example usage.

---

## Thread Safety

**Most tview functions cannot safely be called from any thread except the main one**.

Using either of the following functions, we can queue a function to be executed in the main thread.

* [Application.QueueUpdate](https://godoc.org/github.com/rivo/tview#Application.QueueUpdate)
* [Application.QueueUpdateDraw](https://godoc.org/github.com/rivo/tview#Application.QueueUpdateDraw)

The only difference between the two is that QueueUpdateDraw calls [Application.Draw](https://godoc.org/github.com/rivo/tview#Application.Draw) after the queued function returns.

One exception is [TextView.Write](https://godoc.org/github.com/rivo/tview#TextView.Write), which may safely be called from multiple goroutines.

Below is an example of setting a new root primitive from another goroutine.

{{< highlight go >}}
app.QueueUpdateDraw(func() {
	app.SetRoot(appGrid, true)
})
{{< / highlight >}}

## Example Application

A tview application is constructed of a running [Application](https://godoc.org/github.com/rivo/tview#Application) with at least one root widget.

To display a primitive (and its contents), we call [Application.SetRoot](https://godoc.org/github.com/rivo/tview#Application.SetRoot).

This function has two arguments, a primitive which will become the root of the screen, and a boolean which controls whether the primitive will be resized to fit the screen.

In this example, the root is a Grid containing a label, an input and a submit button.  For a more complex example, see [netris](https://gitlab.com/tslocum/netris).

Install tview if you haven't already:

{{< highlight command >}}
go get -u github.com/rivo/tview
{{< / highlight >}}

Then create a file named greet.go:

{{< highlight go >}}
package main

import (
	"fmt"
	"log"
	"strings"

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

func main() {
	// Initialize application
	app := tview.NewApplication()

	// Create label
	label := tview.NewTextView().SetText("Please enter your name:")

	// Create input field
	input := tview.NewInputField()

	// Create submit button
	btn := tview.NewButton("Submit")

	// Create empty Box to pad each side of appGrid
	bx := tview.NewBox()

	// Create Grid containing the application's widgets
	appGrid := tview.NewGrid().
		SetColumns(-1, 24, 16, -1).
		SetRows(-1, 2, 3, -1).
		AddItem(bx, 0, 0, 3, 1, 0, 0, false). // Left - 3 rows
		AddItem(bx, 0, 1, 1, 1, 0, 0, false). // Top - 1 row
		AddItem(bx, 0, 3, 3, 1, 0, 0, false). // Right - 3 rows
		AddItem(bx, 3, 1, 1, 1, 0, 0, false). // Bottom - 1 row
		AddItem(label, 1, 1, 1, 1, 0, 0, false).
		AddItem(input, 1, 2, 1, 1, 0, 0, false).
		AddItem(btn, 2, 1, 1, 2, 0, 0, false)

	// submittedName is toggled each time Enter is pressed
	var submittedName bool

	// Capture user input
	app.SetInputCapture(func(event *tcell.EventKey) *tcell.EventKey {
		// Anything handled here will be executed on the main thread
		switch event.Key() {
		case tcell.KeyEnter:
			submittedName = !submittedName

			if submittedName {
				name := input.GetText()
				if strings.TrimSpace(name) == "" {
					name = "Anonymous"
				}

				// Create a modal dialog
				m := tview.NewModal().
					SetText(fmt.Sprintf("Greetings, %s!", name)).
					AddButtons([]string{"Hello"})

				// Display and focus the dialog
				app.SetRoot(m, true).SetFocus(m)
			} else {
				// Clear the input field
				input.SetText("")

				// Display appGrid and focus the input field
				app.SetRoot(appGrid, true).SetFocus(input)
			}
			return nil
		case tcell.KeyEsc:
			// Exit the application
			app.Stop()
			return nil
		}

		return event
	})

	// Set the grid as the application root and focus the input field
	app.SetRoot(appGrid, true).SetFocus(input)

	// Run the application
	err := app.Run()
	if err != nil {
		log.Fatal(err)
	}
}
{{< / highlight >}}