widgets, widgets/material: add RadioButton & Enum

Signed-off-by: Alexander Arin <fralx@yandex.ru>

widget/enum.go

@@ -0,0 +1,51 @@
+package widget
+
+import (
+	"gioui.org/gesture"
+	"gioui.org/layout"
+)
+
+type Enum struct {
+	clicks []gesture.Click
+	values []string
+	value  string
+}
+
+func index(vs []string, t string) int {
+	for i, v := range vs {
+		if v == t {
+			return i
+		}
+	}
+	return -1
+}
+
+// Value processes events and returns the last selected value, or
+// the empty string.
+func (e *Enum) Value(gtx *layout.Context) string {
+	for i := range e.clicks {
+		for _, ev := range e.clicks[i].Events(gtx) {
+			switch ev.Type {
+			case gesture.TypeClick:
+				e.value = e.values[i]
+			}
+		}
+	}
+	return e.value
+}
+
+// Layout adds the event handler for key.
+func (rg *Enum) Layout(gtx *layout.Context, key string) {
+	if index(rg.values, key) == -1 {
+		rg.values = append(rg.values, key)
+		rg.clicks = append(rg.clicks, gesture.Click{})
+		rg.clicks[len(rg.clicks)-1].Add(gtx.Ops)
+	} else {
+		idx := index(rg.values, key)
+		rg.clicks[idx].Add(gtx.Ops)
+	}
+}
+
+func (rg *Enum) SetValue(value string) {
+	rg.value = value
+}