Add dropdown button event handling

app/src/ui/app-menu/menu-list-item.tsx

@@ -140,10 +140,7 @@ export class MenuListItem extends React.Component<IMenuListItemProps, {}> {
     }
 
     return (
-      <AccessText
-        text={item.label}
-        highlight={this.props.highlightAccessKey}
-      />
+      <AccessText text={item.label} highlight={this.props.highlightAccessKey} />
     )
   }
 

app/src/ui/app-menu/menu-pane.tsx

@@ -138,15 +138,21 @@ export class MenuPane extends React.Component<IMenuPaneProps> {
   }
 
   private tryMoveSelectionByFirstCharacter(key: string, source: ClickSource) {
-    if (key.length > 1 || !isPrintableCharacterKey(key) || !this.props.allowFirstCharacterNavigation) {
+    if (
+      key.length > 1 ||
+      !isPrintableCharacterKey(key) ||
+      !this.props.allowFirstCharacterNavigation
+    ) {
       return
     }
     const { items, selectedItem } = this.props
-    const char = key.toLowerCase();
+    const char = key.toLowerCase()
     const currentRow = selectedItem ? items.indexOf(selectedItem) + 1 : 0
-    const start = currentRow + 1 > items.length ? 0 : currentRow + 1;
+    const start = currentRow + 1 > items.length ? 0 : currentRow + 1
 
-    const firstChars = items.map(v => v.type === 'separator' ? '' : v.label.trim()[0].toLowerCase())
+    const firstChars = items.map(v =>
+      v.type === 'separator' ? '' : v.label.trim()[0].toLowerCase()
+    )
 
     // Check menu items after selected
     let ix: number = firstChars.indexOf(char, start)
@@ -286,5 +292,5 @@ const supportedKeys = [
 const isSupportedKey = (key: string): key is typeof supportedKeys[number] =>
   (supportedKeys as readonly string[]).includes(key)
 
-const isPrintableCharacterKey = (key: string) => key.length === 1 && key.match(/\S/);
-  
+const isPrintableCharacterKey = (key: string) =>
+  key.length === 1 && key.match(/\S/)

app/src/ui/dropdown-select-button.tsx

@@ -70,6 +70,7 @@ export class DropdownSelectButton<
   IDropdownSelectButtonState<T>
 > {
   private invokeButtonRef: HTMLButtonElement | null = null
+  private dropdownButtonRef: HTMLButtonElement | null = null
   private optionsContainerRef: HTMLDivElement | null = null
 
   public constructor(props: IDropdownSelectButtonProps<T>) {
@@ -140,12 +141,13 @@ export class DropdownSelectButton<
     depth: number | undefined,
     event: React.KeyboardEvent<HTMLDivElement>
   ) => {
-    if (event.key !== 'Escape') {
+    if (event.key !== 'Escape' && event.key !== 'Esc') {
       return
     }
 
     event.preventDefault()
     event.stopPropagation()
+    this.dropdownButtonRef?.focus()
     this.setState({ showButtonOptions: false })
   }
 
@@ -167,10 +169,58 @@ export class DropdownSelectButton<
     this.setState({ showButtonOptions: !this.state.showButtonOptions })
   }
 
+  private onDropdownButtonKeyDown = (
+    event: React.KeyboardEvent<HTMLButtonElement>
+  ) => {
+    const { key } = event
+    let flag = false
+
+    switch (key) {
+      case ' ':
+      case 'Enter':
+      case 'ArrowDown':
+      case 'Down':
+        this.setState({
+          selectedOption: this.props.options.at(0) ?? null,
+          showButtonOptions: true,
+        })
+        flag = true
+        break
+
+      case 'Esc':
+      case 'Escape':
+        this.dropdownButtonRef?.focus()
+        this.setState({ showButtonOptions: false })
+        flag = true
+        break
+
+      case 'Up':
+      case 'ArrowUp':
+        this.setState({
+          selectedOption: this.props.options.at(-1) ?? null,
+          showButtonOptions: true,
+        })
+        flag = true
+        break
+
+      default:
+        break
+    }
+
+    if (flag) {
+      event.stopPropagation()
+      event.preventDefault()
+    }
+  }
+
   private onInvokeButtonRef = (buttonRef: HTMLButtonElement | null) => {
     this.invokeButtonRef = buttonRef
   }
 
+  private onDropdownButtonRef = (buttonRef: HTMLButtonElement | null) => {
+    this.dropdownButtonRef = buttonRef
+  }
+
   private onOptionsContainerRef = (ref: HTMLDivElement | null) => {
     this.optionsContainerRef = ref
   }
@@ -284,6 +334,8 @@ export class DropdownSelectButton<
           <Button
             className={dropdownClasses}
             onClick={this.openSplitButtonDropdown}
+            onKeyDown={this.onDropdownButtonKeyDown}
+            onButtonRef={this.onDropdownButtonRef}
             type="button"
             ariaExpanded={showButtonOptions}
             ariaHaspopup={true}

app/src/ui/lib/button.tsx

@@ -27,6 +27,12 @@ export interface IButtonProps {
    */
   readonly onMouseEnter?: (event: React.MouseEvent<HTMLButtonElement>) => void
 
+  /**
+   * A function that's called when the user moves over the button with
+   * a pointer device.
+   */
+  readonly onKeyDown?: (event: React.KeyboardEvent<HTMLButtonElement>) => void
+
   /** An optional tooltip to render when hovering over the button */
   readonly tooltip?: string
 
@@ -185,6 +191,7 @@ export class Button extends React.Component<IButtonProps, {}> {
       <button
         className={className}
         onClick={disabled ? preventDefault : this.onClick}
+        onKeyDown={this.props.onKeyDown}
         onContextMenu={disabled ? preventDefault : this.onContextMenu}
         type={this.props.type || 'button'}
         ref={this.innerButtonRef}