Domain entry special cases

[w3suli]

Checklist

• I have searched the issue tracker for open issues that relate to the same feature, before opening a new one.
• This issue only relates to a single feature. I will open new issues for any other features.

Is your feature request related to a problem?

I am creating a domain input field in the fyne graphical environment.
The basic input is easy to filter, but there were problems.
The domain name cannot contain two dots in a row.
There cannot be a hyphen before or after the period.
My questions:
If, while typing, the user moves the cursor in the already typed text. Is it possible to scan the character before the cursor and the character after the cursor?
If the user selects a piece of text, can the character before and after the selection be read?
The goal is to prevent the user from writing or pasting text that invalidates the already entered domain name.

Is it possible to construct a solution with the existing API?

No response

Describe the solution you'd like to see.

I would like to detect when the user clicks on the entry and then request the characters before and after the cursor in the program.
I would like to detect when the user clicks in the entry and selects a text section and then request the characters before and after the selection in the program.

[andydotxyz]

It sounds like a case for Validation.

Otherwise an extended Entry where you intercept the TypedRune and paste functionality to do as you desire.

[dweymouth]

If you extend Entry and override the TypedKey function, you will intercept every character and can choose whether to pass it along to the underlying widget.Entry. You can check the current text (entry.Text) and the cursor column, and you should be able to write whatever logic you need to accept or reject that character

[w3suli]

I solved the first problem, but I can't manage the second one.
The start and stop values ​​also included in the function below are required, which I cannot achieve. This is what I need: start, stop := e.selection(). However, I cannot access e.selection().

func (e *Entry) SelectedText() string {
	e.propertyLock.RLock()
	defer e.propertyLock.RUnlock()

	if !e.selecting {
		return ""
	}

	start, stop := e.selection()
	if start == stop {
		return ""
	}
	r := ([]rune)(e.textProvider().String())
	return string(r[start:stop])
}

[andydotxyz]

The cursor position will be at the end of the selection, and the start will be len(e.SelectedText()) runes earlier.

[w3suli]

Unfortunately not. That's what I thought at first too.
Text can be selected not only from left to right, but also from right to left.
Also, there may be repeated sections of text, and in this case, even scanning the text on both sides of the cursor and comparing it with the content of the selected section does not guarantee the correct position.

[andydotxyz]

Text can be selected not only from left to right, but also from right to left.

Hmm I see. I will have to think about that - but you could keep track of the cursor position when selection is set, then follow it for changes. Not ideal but that is possible with existing API...

Also, there may be repeated sections of text, and in this case, even scanning the text on both sides of the cursor and comparing it with the content of the selected section does not guarantee the correct position.

Absolutely - that is not a suitable solution.

[w3suli]

To extract the characters before and after the cursor position, e.CursorColumn can be used well (e.Text[e.CursorColumn]), so part of the problem is solved.
However, I do not have access to the starting and ending positions of the selection. Would there be a way to query the start and end position of the marking?

[andydotxyz]

func main() {
	a := app.New()
	w := a.NewWindow("Hello")

	hello := widget.NewLabel("")
	ent := widget.NewEntry()
	selstart := -1
	ent.OnCursorChanged = func() {
		pos := ent.CursorColumn
		text := ent.SelectedText()
		if text == "" {
			hello.SetText("No selection")
			selstart = -1
			return
		}
		pos2 := 0
		if selstart == -1 {
			selstart = ent.CursorColumn
		}

		if ent.CursorColumn >= selstart {
			pos = ent.CursorColumn - len(text)
		}
		pos2 = pos + len(text)

		info := fmt.Sprintf("Selection \"%s\", range %d:%d", text, pos, pos2)
		hello.SetText(info)
	}
	w.SetContent(container.NewVBox(
		hello,
		ent,
	))

	w.ShowAndRun()
}

[w3suli]

Partly true. I didn't think of that, thanks!
There is one problem with the solution:
If the user clicks into the text and then presses the Shift key to make the selection, strange results can occur.
Example:
0123456789
In the number line above, by placing the cursor after the number eight, then pressing the Shift key and clicking behind the number three, the program returns the value -2:3 (the correct value would be 3:8).
Or by clicking after the nine and pressing Shift, then clicking after the four, the result will be -1:4 (the correct one would be 4:9).
Or clicking after the seven and holding down the shift key and clicking after the single will result in -5:1 instead of a1:7.

[andydotxyz]

// Package main loads a very basic Hello World graphical application.
package main

import (
	"fmt"

	"fyne.io/fyne/v2/app"
	"fyne.io/fyne/v2/container"
	"fyne.io/fyne/v2/widget"
)

func main() {
	a := app.New()
	w := a.NewWindow("Hello")

	hello := widget.NewLabel("")
	ent := widget.NewEntry()
	selstart := -1
	lastCol := 0
	ent.OnCursorChanged = func() {
		pos := ent.CursorColumn
		text := ent.SelectedText()
		if text == "" {
			hello.SetText("No selection")
			lastCol = pos
			selstart = -1
			return
		}
		pos2 := 0
		if selstart == -1 {
			selstart = lastCol
		}

		if ent.CursorColumn >= selstart {
			pos = ent.CursorColumn - len(text)
		}
		pos2 = pos + len(text)

		info := fmt.Sprintf("Selection \"%s\", range %d:%d", text, pos, pos2)
		hello.SetText(info)
	}
	w.SetContent(container.NewVBox(
		hello,
		ent,
	))

	w.ShowAndRun()
}

[w3suli]

Looks good, thank you very much!