[GH-ISSUE #409] Application.SetInputCapture doesn't seem to capture anything

kerem commented

2026-03-04 01:03:44 +03:00

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Originally created by @Abenstex on GitHub (Feb 18, 2020).
Original GitHub issue: https://github.com/rivo/tview/issues/409

I setup an application with pages. When the user presses a key combination the pages should be changed. However, trying to capture the key events does not appear to do anything:
`app := tview.NewApplication()

mainGrid := uiElements.BuildMainGrid(*app)

mainGrid.AddPage(uiElements.NewWelcomePanel(), "Welcome", true, true, 0)
mainGrid.AddPage(uiElements.NewTopLevelUserManagementPanel(), "Users", true, true, 1)
mainGrid.Pages.SwitchToPage("Welcome")

/*app.SetInputCapture(func(event *tcell.EventKey) *tcell.EventKey {
	if event == tcell.NewEventKey(tcell.KeyRune, '1', tcell.ModAlt) {
		mainGrid.Pages.SwitchToPage("Users")
	} else if event == tcell.NewEventKey(tcell.KeyRune, '0', tcell.ModAlt) {
		mainGrid.Pages.SwitchToPage("Welcome")
	} 
	return event
})*/
app.SetInputCapture(func(event *tcell.EventKey) *tcell.EventKey {
	if event.Key() == tcell.KeyCtrlN {
		fmt.Fprintf(mainGrid.InfoBar, `%d ["%d"][darkcyan]%s[white][""]  `, 42, 42, "Foo")
	} else if event.Key() == tcell.KeyCtrlP {
		fmt.Fprintf(mainGrid.InfoBar, `%d ["%d"][darkcyan]%s[white][""]  `, 42, 42, "Bar")
	}
	return event
})

if err := tview.NewApplication().SetRoot(mainGrid.Grid, true).Run(); err != nil {
	panic(err)
}`

When I call mainGrid.Pages.SwitchToPage("Welcome") without waiting for key presses then the correct page is shown, though. To debug I just wanted to print something to a Textview, but that isn't working either. So my question is what am I missing or doing wrong?

Originally created by @Abenstex on GitHub (Feb 18, 2020). Original GitHub issue: https://github.com/rivo/tview/issues/409 I setup an application with pages. When the user presses a key combination the pages should be changed. However, trying to capture the key events does not appear to do anything: `app := tview.NewApplication() mainGrid := uiElements.BuildMainGrid(*app) mainGrid.AddPage(uiElements.NewWelcomePanel(), "Welcome", true, true, 0) mainGrid.AddPage(uiElements.NewTopLevelUserManagementPanel(), "Users", true, true, 1) mainGrid.Pages.SwitchToPage("Welcome") /*app.SetInputCapture(func(event *tcell.EventKey) *tcell.EventKey { if event == tcell.NewEventKey(tcell.KeyRune, '1', tcell.ModAlt) { mainGrid.Pages.SwitchToPage("Users") } else if event == tcell.NewEventKey(tcell.KeyRune, '0', tcell.ModAlt) { mainGrid.Pages.SwitchToPage("Welcome") } return event })*/ app.SetInputCapture(func(event *tcell.EventKey) *tcell.EventKey { if event.Key() == tcell.KeyCtrlN { fmt.Fprintf(mainGrid.InfoBar, `%d ["%d"][darkcyan]%s[white][""] `, 42, 42, "Foo") } else if event.Key() == tcell.KeyCtrlP { fmt.Fprintf(mainGrid.InfoBar, `%d ["%d"][darkcyan]%s[white][""] `, 42, 42, "Bar") } return event }) if err := tview.NewApplication().SetRoot(mainGrid.Grid, true).Run(); err != nil { panic(err) }` When I call `mainGrid.Pages.SwitchToPage("Welcome")` without waiting for key presses then the correct page is shown, though. To debug I just wanted to print something to a Textview, but that isn't working either. So my question is what am I missing or doing wrong?

kerem closed this issue

2026-03-04 01:03:44 +03:00

kerem commented

2026-03-04 01:03:45 +03:00

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@tslocum commented on GitHub (Feb 18, 2020):

Hey @Abenstex. Did you read the relevant documentation before submitting this? It states:

TextView is a box which displays text. It implements the io.Writer interface so you can stream text to it. This does not trigger a redraw automatically but if a handler is installed via SetChangedFunc(), you can cause it to be redrawn.

Setting a handler via SetChangedFunc which calls Application.Draw whenever the TextView is changed will resolve this. You could also make any text changes first and then manually trigger an application draw by calling Application.QueueUpdateDraw with an empty function.

@tslocum commented on GitHub (Feb 18, 2020): Hey @Abenstex. Did you read the [relevant documentation](https://godoc.org/github.com/rivo/tview#TextView) before submitting this? It states: `TextView is a box which displays text. It implements the io.Writer interface so you can stream text to it. This does not trigger a redraw automatically but if a handler is installed via SetChangedFunc(), you can cause it to be redrawn. ` Setting a handler via SetChangedFunc which calls Application.Draw whenever the TextView is changed will resolve this. You could also make any text changes first and then [manually trigger an application draw](https://rocketnine.space/post/tview-and-you/#thread-safety) by calling Application.QueueUpdateDraw with an empty function.

kerem commented

2026-03-04 01:03:45 +03:00

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@Abenstex commented on GitHub (Feb 19, 2020):

@tslocum thanks for your reply. As a matter of fact I hadn't read that part or didn't remember it. Anyway, what I did then was to include the following lines app.QueueUpdateDraw(func() { app.SetRoot(mainGrid.Grid, true) }) mainGrid.InfoBar.SetChangedFunc(func() { app.Draw() })
First I only called app.QueueUpdateDraw but since that didn't help I added mainGrid.InfoBar.SetChangedFunc. Unfortunately it still isn't captchuring any key events at least not visibly.

@Abenstex commented on GitHub (Feb 19, 2020): @tslocum thanks for your reply. As a matter of fact I hadn't read that part or didn't remember it. Anyway, what I did then was to include the following lines `app.QueueUpdateDraw(func() { app.SetRoot(mainGrid.Grid, true) }) mainGrid.InfoBar.SetChangedFunc(func() { app.Draw() })` First I only called `app.QueueUpdateDraw` but since that didn't help I added `mainGrid.InfoBar.SetChangedFunc`. Unfortunately it still isn't captchuring any key events at least not visibly.

kerem commented

2026-03-04 01:03:45 +03:00

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@Abenstex commented on GitHub (Feb 19, 2020):

As a matter of fact I included
app.SetInputCapture(func(event *tcell.EventKey) *tcell.EventKey { panic(errors.New("Key event: "+event.Name())) ... but the program doesn't even panic. So somehow I'm missing something essential

@Abenstex commented on GitHub (Feb 19, 2020): As a matter of fact I included `app.SetInputCapture(func(event *tcell.EventKey) *tcell.EventKey { panic(errors.New("Key event: "+event.Name())) ...` but the program doesn't even panic. So somehow I'm missing something essential

kerem commented

2026-03-04 01:03:45 +03:00

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@rivo commented on GitHub (Feb 19, 2020):

You're creating a variable app somewhere to which SetInputCapture() is attached. But you're not using it to run the application. You actually create another Application (with tview.NewApplication()) object when you start your session. That's why SetInputCapture() has no effect.

Here's an example that should work:

package main

import (
	"fmt"

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

func main() {
	pages := tview.NewPages()
	pages.AddPage("users", tview.NewBox().SetTitle("Users").SetBorder(true), true, true)
	pages.AddPage("welcome", tview.NewBox().SetTitle("Welcome").SetBorder(true), true, true)

	info := tview.NewTextView().SetDynamicColors(true).SetRegions(true)

	grid := tview.NewGrid().SetRows(0, 1)
	grid.AddItem(pages, 0, 0, 1, 1, 0, 0, true)
	grid.AddItem(info, 1, 0, 1, 1, 0, 0, false)

	app := tview.NewApplication()
	app.SetInputCapture(func(event *tcell.EventKey) *tcell.EventKey {
		if event.Key() == tcell.KeyCtrlN {
			pages.SwitchToPage("users")
			fmt.Fprintf(info, `%d ["%d"][darkcyan]%s[white][""]  `, 42, 42, "Foo")
		} else if event.Key() == tcell.KeyCtrlP {
			pages.SwitchToPage("welcome")
			fmt.Fprintf(info, `%d ["%d"][darkcyan]%s[white][""]  `, 42, 42, "Bar")
		}
		return event
	})

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

You also don't need to call app.Draw() as @tslocum suggested because the handler provided with the SetInputCapture() function will always be called as part of the main goroutine and a call to app.Draw() will follow implicitly. See here for more information.

@rivo commented on GitHub (Feb 19, 2020): You're creating a variable `app` somewhere to which `SetInputCapture()` is attached. But you're not using it to run the application. You actually create another `Application` (with `tview.NewApplication()`) object when you start your session. That's why `SetInputCapture()` has no effect. Here's an example that should work: ```go package main import ( "fmt" "github.com/gdamore/tcell" "github.com/rivo/tview" ) func main() { pages := tview.NewPages() pages.AddPage("users", tview.NewBox().SetTitle("Users").SetBorder(true), true, true) pages.AddPage("welcome", tview.NewBox().SetTitle("Welcome").SetBorder(true), true, true) info := tview.NewTextView().SetDynamicColors(true).SetRegions(true) grid := tview.NewGrid().SetRows(0, 1) grid.AddItem(pages, 0, 0, 1, 1, 0, 0, true) grid.AddItem(info, 1, 0, 1, 1, 0, 0, false) app := tview.NewApplication() app.SetInputCapture(func(event *tcell.EventKey) *tcell.EventKey { if event.Key() == tcell.KeyCtrlN { pages.SwitchToPage("users") fmt.Fprintf(info, `%d ["%d"][darkcyan]%s[white][""] `, 42, 42, "Foo") } else if event.Key() == tcell.KeyCtrlP { pages.SwitchToPage("welcome") fmt.Fprintf(info, `%d ["%d"][darkcyan]%s[white][""] `, 42, 42, "Bar") } return event }) if err := app.SetRoot(grid, true).Run(); err != nil { panic(err) } } ``` You also don't need to call `app.Draw()` as @tslocum suggested because the handler provided with the `SetInputCapture()` function will always be called as part of the main goroutine and a call to `app.Draw()` will follow implicitly. See [here](https://github.com/rivo/tview/wiki/Concurrency) for more information.

kerem commented

2026-03-04 01:03:45 +03:00

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@Abenstex commented on GitHub (Feb 19, 2020):

Oh damn...sorry I really didn't see that. Sometimes you just don't see the forest for the trees.

@Abenstex commented on GitHub (Feb 19, 2020): Oh damn...sorry I really didn't see that. Sometimes you just don't see the forest for the trees.

kerem referenced this issue

2026-03-04 01:08:30 +03:00

[PR #301] Added FormItem Validation #903

kerem referenced this issue

2026-03-04 01:08:30 +03:00

[PR #300] Added collection of FormItemArgs for each of the form FormItem types #904

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[GH-ISSUE #409] Application.SetInputCapture doesn't seem to capture anything #300