Question about textview refreshing content in real time

[7yyo]

After adding setDoneFunc to an item, execute a piece of code logic. This process will print some logs. These logs will be transferred to another textview for display. However, the program can only display all logs after setDoneFunc ends and will not output them in real time. This Why? I can provide pseudocode if necessary. The code is similar to the demo of textview

[rivo]

Yes, please provide some brief code that can be run to reproduce this.

[7yyo]

@rivo Thanks for the response. The following code can be run directly. There is a treeView and a textView. When setDoneFunc is executed, some strings will be output to textView for display, but they can only be displayed after setDoneFunc is executed. Strings cannot be printed out in textView in real time.

package main

import (
	"fmt"
	"github.com/gdamore/tcell/v2"
	"github.com/rivo/tview"
	"time"
)

func main() {
	app := tview.NewApplication()
	grid := tview.NewGrid().SetRows(0, 0).SetColumns(0, 0)
	treeView := tview.NewTreeView()
	root := tview.NewTreeNode("hello world - tree")
	treeView.SetRoot(root).SetCurrentNode(root).SetTitle("tree").SetBorder(true)
	textView := tview.NewTextView()
	textView.SetTitle("text").SetBorder(true)
	textView.SetChangedFunc(func() {
		app.Draw()
	})
	grid.AddItem(treeView, 0, 0, 1, 1, 0, 0, true)
	grid.AddItem(textView, 1, 0, 1, 1, 0, 0, true)

	treeView.SetDoneFunc(func(key tcell.Key) {
		fmt.Fprintf(textView, "%v - %s\n", time.Now(), "hello")
		time.Sleep(1000 * time.Millisecond)
		fmt.Fprintf(textView, "%v - %s\n", time.Now(), "world")
		time.Sleep(5000 * time.Millisecond)
		fmt.Fprintf(textView, "%v - %s\n", time.Now(), "tview")
	})

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

[rivo]

@digitallyserviced is generally right in that your SetDoneFunc is part of the main goroutine. So if you're blocking that function (with your sleep calls, in this example), you're blocking everything basically. If you want to stream text to your TextView, you need to do it from a separate goroutine. If you know all text in advance, however, just use SetText() without the time.Sleep calls (no goroutine needed in that case).

A few additional notes:

• Just call app.Draw() from your SetChangedFunc. No need to call QueueUpdateDraw() like @digitallyserviced suggested (see the documentation for details).
• The SetDoneFunc can be used in theory but it's usually reserved to be used internally for forms. (Yes, it shouldn't have been exposed in the first place.) Maybe SetSelectedFunc or SetInputCapture with your own bindings is better.
• The .SetRows(0, 0).SetColumns(0, 0) calls are not needed: "A value of 0 is assumed for any undefined column.".

[7yyo]

@rivo @digitallyserviced thanks!
To summarize, this code solves the problem I raised

package main

import (
	"fmt"
	"github.com/gdamore/tcell/v2"
	"github.com/rivo/tview"
	"time"
)

func main() {
	app := tview.NewApplication()
	grid := tview.NewGrid().SetRows(0, 0).SetColumns(0, 0)
	treeView := tview.NewTreeView()
	root := tview.NewTreeNode("hello world - tree")
	treeView.SetRoot(root).SetCurrentNode(root).SetTitle("tree").SetBorder(true)
	textView := tview.NewTextView()
	textView.SetTitle("text").SetBorder(true)
	textView.SetChangedFunc(func() {
		app.Draw()
	})
	grid.AddItem(treeView, 0, 0, 1, 1, 0, 0, true)
	grid.AddItem(textView, 1, 0, 1, 1, 0, 0, true)

	treeView.SetDoneFunc(func(key tcell.Key) {
		go func() {
			fmt.Fprintf(textView, "%v - %s\n", time.Now(), "hello")
			time.Sleep(1000 * time.Millisecond)
			fmt.Fprintf(textView, "%v - %s\n", time.Now(), "world")
			time.Sleep(5000 * time.Millisecond)
			fmt.Fprintf(textView, "%v - %s\n", time.Now(), "tview")
			grid.RemoveItem(treeView)
		}()
	})

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

However, I added grid.RemoveItem(treeView) and tried to delete the treeview before the goroutine ended, but it failed. Why is this?

[rivo]

You can't make other, especially structural changes to your widgets in a separate goroutine. For example, if the application is currently re-drawing the screen while you change objects that need to be drawn, you will run in to race issues. (The io.Reader interface of TextView is an exception here.)

Please read the following article about concurrency in tview:

https://github.com/rivo/tview/wiki/Concurrency

For your specific program, you will have to wrap grid.RemoveItem(treeView) in a app.QueueUpdateDraw().

[7yyo]

@rivo I modified it like this but it still doesn't work. What's the problem?

	treeView.SetDoneFunc(func(key tcell.Key) {
		go func() {
			fmt.Fprintf(textView, "%v - %s\n", time.Now(), "hello")
			time.Sleep(1000 * time.Millisecond)
			fmt.Fprintf(textView, "%v - %s\n", time.Now(), "world")
			time.Sleep(1000 * time.Millisecond)
			fmt.Fprintf(textView, "%v - %s\n", time.Now(), "tview")
			time.Sleep(1000 * time.Millisecond)
			go func() {
				app.QueueUpdateDraw(func() {
					grid.RemoveItem(textView)
				})
			}()
		}()
	})

[rivo]

You don't need the second goroutine.

Can you be a bit more specific? What exactly does not work?

[7yyo]

@rivo The code is like this, but textview cannot be automatically hidden

func main() {
	app := tview.NewApplication()
	grid := tview.NewGrid().SetRows(0, 0).SetColumns(0, 0)
	treeView := tview.NewTreeView()
	root := tview.NewTreeNode("hello world - tree")
	treeView.SetRoot(root).SetCurrentNode(root).SetTitle("tree").SetBorder(true)
	textView := tview.NewTextView()
	textView.SetTitle("text").SetBorder(true)
	textView.SetChangedFunc(func() {
		app.Draw()
	})
	grid.AddItem(treeView, 0, 0, 1, 1, 0, 0, true)
	grid.AddItem(textView, 1, 0, 1, 1, 0, 0, true)

	treeView.SetDoneFunc(func(key tcell.Key) {
		go func() {
			fmt.Fprintf(textView, "%v - %s\n", time.Now(), "hello")
			time.Sleep(1000 * time.Millisecond)
			fmt.Fprintf(textView, "%v - %s\n", time.Now(), "world")
			time.Sleep(1000 * time.Millisecond)
			fmt.Fprintf(textView, "%v - %s\n", time.Now(), "tview")
			time.Sleep(1000 * time.Millisecond)
			app.QueueUpdateDraw(func() {
				grid.RemoveItem(textView)
			})
		}()
	})
	if err := app.SetRoot(grid, true).EnableMouse(true).Run(); err != nil {
		panic(err)
	}
}

[rivo]

It did disappear but the screen was not cleared before redrawing everything so you could still see the remainders of the last app.Draw cycle. With the latest commit, the application will always clear the screen before drawing all elements. Try your example with the newest version of tview.

[7yyo]

@rivo After updating to the latest version, it really works. This project is so cool and the updates are timely. Thanks for the help, I will always support it!

[rivo]

@7yyo Thank you for the nice words. I try to fix bugs quickly but there may be times when I'm too busy to respond as quickly as I have in this case. Any way, I'm glad it works now.