feat(dropdown): Draw rune at the end of the field to indicate that this field is a dropdown

dropdown.go

@@ -127,6 +127,9 @@ type DropDown struct {
 	// The chars to show when the option's text gets shortened.
 	abbreviationChars string
 
+	// The symbol to draw at the end of the field.
+	dropDownSymbol rune
+
 	sync.RWMutex
 }
 
@@ -151,6 +154,7 @@ func NewDropDown() *DropDown {
 		fieldTextColor:              Styles.PrimaryTextColor,
 		fieldTextColorFocused:       Styles.PrimaryTextColor,
 		prefixTextColor:             Styles.ContrastSecondaryTextColor,
+		dropDownSymbol:              Styles.DropDownSymbol,
 		abbreviationChars:           Styles.DropDownAbbreviationChars,
 	}
 
@@ -159,6 +163,15 @@ func NewDropDown() *DropDown {
 	return d
 }
 
+// SetDropDownSymbolRune sets the rune to be drawn at the end of the dropdown field
+// to indicate that this field is a dropdown.
+func (d *DropDown) SetDropDownSymbolRune(symbol rune) *DropDown {
+	d.Lock()
+	defer d.Unlock()
+	d.dropDownSymbol = symbol
+	return d
+}
+
 // SetCurrentOption sets the index of the currently selected option. This may
 // be a negative value to indicate that no option is currently selected. Calling
 // this function will also trigger the "selected" callback (if there is one).
@@ -398,6 +411,7 @@ func (d *DropDown) getFieldWidth() int {
 	}
 	fieldWidth += len(d.optionPrefix) + len(d.optionSuffix)
 	fieldWidth += len(d.currentOptionPrefix) + len(d.currentOptionSuffix)
+	fieldWidth += 3 // space + dropDownSymbol + space
 	return fieldWidth
 }
 
@@ -589,6 +603,9 @@ func (d *DropDown) Draw(screen tcell.Screen) {
 		Print(screen, text, x, y, fieldWidth, AlignLeft, color)
 	}
 
+	// Draw drop down symbol
+	screen.SetContent(x+fieldWidth-2, y, d.dropDownSymbol, nil, new(tcell.Style).Foreground(fieldTextColor).Background(fieldBackgroundColor))
+
 	// Draw options list.
 	if hasFocus && d.open {
 		// We prefer to drop down but if there is no space, maybe drop up?

styles.go

@@ -36,6 +36,7 @@ type Theme struct {
 
 	// Drop down
 	DropDownAbbreviationChars string // The chars to show when the option's text gets shortened.
+	DropDownSymbol            rune   // The symbol to draw at the end of the field.
 }
 
 // Styles defines the appearance of an application. The default is for a black
@@ -67,4 +68,5 @@ var Styles = Theme{
 	CheckBoxCheckedRune: 'X',
 
 	DropDownAbbreviationChars: "...",
+	DropDownSymbol:            '▼',
 }