TextBox can receive EditAction commands

This makes it possible for another widget to tell the TextBox
to perform some edit action, such as modifying the selection or
replacing the text.

druid/src/widget/textbox.rs

@@ -51,6 +51,9 @@ pub struct TextBox {
 }
 
 impl TextBox {
+    /// Perform an `EditAction`. The payload *must* be an `EditAction`.
+    pub const PERFORM_EDIT: Selector = Selector::new("druid-builtin.textbox.perform-edit");
+
     /// Create a new TextBox widget
     pub fn new() -> TextBox {
         Self {
@@ -237,7 +240,9 @@ impl Widget<String> for TextBox {
 
         match event {
             Event::MouseDown(mouse) => {
-                ctx.request_focus();
+                if !ctx.has_focus() {
+                    ctx.request_focus();
+                }
                 ctx.set_active(true);
 
                 let cursor_offset = self.offset_for_point(mouse.pos, &text_layout);
@@ -289,6 +294,12 @@ impl Widget<String> for TextBox {
                 ctx.set_handled();
             }
             Event::Command(cmd) if cmd.selector == RESET_BLINK => self.reset_cursor_blink(ctx),
+            Event::Command(cmd) if cmd.selector == TextBox::PERFORM_EDIT => {
+                let edit = cmd
+                    .get_object::<EditAction>()
+                    .expect("PERFORM_EDIT contained non-edit payload");
+                self.do_edit_action(edit.to_owned(), data);
+            }
             Event::Paste(ref item) => {
                 if let Some(string) = item.get_string() {
                     edit_action = Some(EditAction::Paste(string));