widget: add Editor.Filter for filtering unwanted characters

Signed-off-by: Elias Naur <mail@eliasnaur.com>

widget/editor.go

@@ -49,6 +49,9 @@ type Editor struct {
 	InputHint key.InputHint
 	// MaxLen limits the editor content to a maximum length. Zero means no limit.
 	MaxLen int
+	// Filter is the list of characters allowed in the Editor. If Filter is empty,
+	// all characters are allowed.
+	Filter string
 
 	eventKey     int
 	font         text.Font
@@ -1235,12 +1238,21 @@ func (e *Editor) replace(start, end int, s string, addHistory bool) int {
 	startPos := e.closestPosition(combinedPos{runes: start})
 	endPos := e.closestPosition(combinedPos{runes: end})
 	startOff := e.runeOffset(startPos.runes)
-	sc := utf8.RuneCountInString(s)
 	el := e.Len()
-	for e.MaxLen > 0 && el+sc > e.MaxLen {
-		_, n := utf8.DecodeLastRuneInString(s)
-		s = s[:len(s)-n]
-		sc--
+	var sc int
+	idx := 0
+	for idx < len(s) {
+		if e.MaxLen > 0 && el+sc >= e.MaxLen {
+			s = s[:idx]
+			break
+		}
+		_, n := utf8.DecodeRuneInString(s[idx:])
+		if e.Filter != "" && !strings.Contains(e.Filter, s[idx:idx+n]) {
+			s = s[:idx] + s[idx+n:]
+			continue
+		}
+		idx += n
+		sc++
 	}
 	newEnd := startPos.runes + sc
 	replaceSize := endPos.runes - startPos.runes

widget/editor_test.go

@@ -1036,6 +1036,37 @@ func TestEditor_MaxLen(t *testing.T) {
 	}
 }
 
+func TestEditor_Filter(t *testing.T) {
+	e := new(Editor)
+
+	e.Filter = "123456789"
+	e.SetText("abcde1234")
+	if got, want := e.Text(), "1234"; got != want {
+		t.Errorf("editor failed to filter SetText")
+	}
+
+	e.SetText("2345678")
+	gtx := layout.Context{
+		Ops:         new(op.Ops),
+		Constraints: layout.Exact(image.Pt(100, 100)),
+		Queue: newQueue(
+			key.EditEvent{Range: key.Range{Start: 0, End: 0}, Text: "ab1"},
+			key.SelectionEvent{Start: 4, End: 4},
+		),
+	}
+	cache := text.NewCache(gofont.Collection())
+	fontSize := unit.Sp(10)
+	font := text.Font{}
+	e.Layout(gtx, cache, font, fontSize, nil)
+
+	if got, want := e.Text(), "12345678"; got != want {
+		t.Errorf("editor failed to filter EditEvent")
+	}
+	if start, end := e.Selection(); start != 2 || end != 2 {
+		t.Errorf("editor failed to adjust SelectionEvent")
+	}
+}
+
 func textWidth(e *Editor, lineNum, colStart, colEnd int) float32 {
 	var w fixed.Int26_6
 	glyphs := e.lines[lineNum].Layout.Glyphs