Improved drop down list usability.

dropdown.go

@@ -140,6 +140,9 @@ type DropDown struct {
 	// The symbol to draw at the end of the field when opened.
 	dropDownOpenSymbol rune
 
+	// The symbol used to draw the selected item when opened.
+	dropDownSelectedSymbol rune
+
 	// A flag that determines whether the drop down symbol is always drawn.
 	alwaysDrawDropDownSymbol bool
 
@@ -166,12 +169,16 @@ func NewDropDown() *DropDown {
 		prefixTextColor:             Styles.ContrastSecondaryTextColor,
 		dropDownSymbol:              Styles.DropDownSymbol,
 		dropDownOpenSymbol:          Styles.DropDownOpenSymbol,
+		dropDownSelectedSymbol:      Styles.DropDownSelectedSymbol,
 		abbreviationChars:           Styles.DropDownAbbreviationChars,
 		labelColorFocused:           ColorUnset,
 		fieldBackgroundColorFocused: ColorUnset,
 		fieldTextColorFocused:       ColorUnset,
 	}
 
+	if sym := d.dropDownSelectedSymbol; sym != 0 {
+		list.SetIndicators(" "+string(sym)+" ", "", "   ", "")
+	}
 	d.focus = d
 
 	return d
@@ -191,6 +198,21 @@ func (d *DropDown) SetDropDownOpenSymbolRune(symbol rune) {
 	d.Lock()
 	defer d.Unlock()
 	d.dropDownOpenSymbol = symbol
+
+	if symbol != 0 {
+		d.list.SetIndicators(" "+string(symbol)+" ", "", "   ", "")
+	} else {
+		d.list.SetIndicators("", "", "", "")
+	}
+
+}
+
+// SetDropDownSelectedSymbolRune sets the rune to be drawn at the start of the
+// selected list item.
+func (d *DropDown) SetDropDownSelectedSymbolRune(symbol rune) {
+	d.Lock()
+	defer d.Unlock()
+	d.dropDownSelectedSymbol = symbol
 }
 
 // SetAlwaysDrawDropDownSymbol sets a flad that determines whether the drop
@@ -415,7 +437,8 @@ func (d *DropDown) getFieldWidth() int {
 	}
 	fieldWidth += len(d.optionPrefix) + len(d.optionSuffix)
 	fieldWidth += len(d.currentOptionPrefix) + len(d.currentOptionSuffix)
-	fieldWidth += 3 // space + dropDownSymbol + space
+	// space <text> space + dropDownSymbol + space
+	fieldWidth += 4
 	return fieldWidth
 }
 

list.go

@@ -194,6 +194,15 @@ type List struct {
 	// The height of the list the last time it was drawn.
 	height int
 
+	// Prefix and suffix strings drawn for unselected elements.
+	unselectedPrefix, unselectedSuffix []byte
+
+	// Prefix and suffix strings drawn for selected elements.
+	selectedPrefix, selectedSuffix []byte
+
+	// Maximum prefix and suffix width.
+	prefixWidth, suffixWidth int
+
 	sync.RWMutex
 }
 
@@ -627,6 +636,24 @@ func (l *List) SetItemEnabled(index int, enabled bool) {
 	item.disabled = !enabled
 }
 
+// SetIndicators is used to set prefix and suffix indicators for selected and unselected items.
+func (l *List) SetIndicators(selectedPrefix, selectedSuffix, unselectedPrefix, unselectedSuffix string) {
+	l.Lock()
+	defer l.Unlock()
+	l.selectedPrefix = []byte(selectedPrefix)
+	l.selectedSuffix = []byte(selectedSuffix)
+	l.unselectedPrefix = []byte(unselectedPrefix)
+	l.unselectedSuffix = []byte(unselectedSuffix)
+	l.prefixWidth = len(selectedPrefix)
+	if len(unselectedPrefix) > l.prefixWidth {
+		l.prefixWidth = len(unselectedPrefix)
+	}
+	l.suffixWidth = len(selectedSuffix)
+	if len(unselectedSuffix) > l.suffixWidth {
+		l.suffixWidth = len(unselectedSuffix)
+	}
+}
+
 // FindItems searches the main and secondary texts for the given strings and
 // returns a list of item indices in which those strings are found. One of the
 // two search strings may be empty, it will then be ignored. Indices are always
@@ -866,7 +893,7 @@ func (l *List) Draw(screen tcell.Screen) {
 	// Determine the dimensions.
 	x, y, width, height := l.GetInnerRect()
 	leftEdge := x
-	fullWidth := width + l.paddingLeft + l.paddingRight
+	fullWidth := width + l.paddingLeft + l.paddingRight + l.prefixWidth + l.suffixWidth
 	bottomLimit := y + height
 
 	l.height = height
@@ -934,7 +961,25 @@ func (l *List) Draw(screen tcell.Screen) {
 			RenderScrollBar(screen, l.scrollBarVisibility, scrollBarX, y, scrollBarHeight, len(l.items), scrollBarCursor, index-l.itemOffset, l.hasFocus, l.scrollBarColor)
 			y++
 			continue
-		} else if item.disabled {
+		}
+
+		if index == l.currentItem {
+			if len(l.selectedPrefix) > 0 {
+				mainText = append(l.selectedPrefix, mainText...)
+			}
+			if len(l.selectedSuffix) > 0 {
+				mainText = append(mainText, l.selectedSuffix...)
+			}
+
+		} else {
+			if len(l.unselectedPrefix) > 0 {
+				mainText = append(l.unselectedPrefix, mainText...)
+			}
+			if len(l.unselectedSuffix) > 0 {
+				mainText = append(mainText, l.unselectedSuffix...)
+			}
+		}
+		if item.disabled {
 			// Shortcuts.
 			if showShortcuts && item.shortcut != 0 {
 				Print(screen, []byte(fmt.Sprintf("(%c)", item.shortcut)), x-5, y, 4, AlignRight, tcell.ColorDarkSlateGray.TrueColor())

styles.go

@@ -39,6 +39,7 @@ type Theme struct {
 	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 when closed.
 	DropDownOpenSymbol        rune   // The symbol to draw at the end of the field when opened.
+	DropDownSelectedSymbol    rune   // The symbol to draw to indicate the selected list item.
 
 	// Scroll bar
 	ScrollBarColor tcell.Color
@@ -80,6 +81,7 @@ var Styles = Theme{
 	DropDownAbbreviationChars: "...",
 	DropDownSymbol:            '◀',
 	DropDownOpenSymbol:        '▼',
+	DropDownSelectedSymbol:    '▶',
 
 	ScrollBarColor: tcell.ColorWhite.TrueColor(),