Controls that bjogui does not wrap, with (bjogui native)

A native is made with a function that makes the control and hooks its
events, and one that puts a value on it. hosted puts it in a view: the
control is made once for its place, given a value only when the view's
value changes, and what it sends while it is given one is dropped. Its
outputs become the app's messages through on-output and view-map, and
may be sent from any thread.

🤖 Generated with [ECA](https://eca.dev) (anthropic/claude-opus-4-8)

Co-Authored-By: eca-agent <git@eca.dev>

Readme.org

@@ -255,6 +255,53 @@ a playhead, marks and a hover line. ~start-headless!~ sets Avalonia up with no
 screen, so that a test can draw components and read their pixels; see
 ~tests/components.bjo~.
 
+* Controls bjogui does not wrap: (bjogui native)
+
+Any control of Avalonia's, or of another package's, can be put in a view.
+The program makes the control and hooks its events itself, so this is the
+one place where it names Avalonia's types.
+
+#+BEGIN_SRC scheme
+(import (std interop))
+(import (bjogui native))
+(import/class (Control (: Avalonia.Controls.Control))
+              (Calendar (: Avalonia.Controls.Calendar (-> Calendar)))
+              (DateTime (: System.DateTime))
+              ((Nullable %a) (: System.Nullable)))
+(import/extern
+  (selected-date (: Avalonia.Controls.Calendar.SelectedDate (-> Calendar (Nullable DateTime)) #:get))
+  (selected-date! (: Avalonia.Controls.Calendar.SelectedDate (-> Calendar (Nullable DateTime) void) #:set))
+  (parse-date (: System.DateTime.Parse (-> string DateTime))))
+
+;; A calendar, for a date as "2026-10-25".
+(: calendar (Native string string))
+(def calendar
+  (native (fun (send)                          ; makes one control
+            (def c (Calendar.))
+            (ignore (add-event-handler! c "SelectedDatesChanged"
+                      (: (fun (s e)
+                           (def d (selected-date c))
+                           (when (.-HasValue d) (send (.ToString (.-Value d) "yyyy-MM-dd"))))
+                         (-> Object Object void))))
+            (cast Control c))
+          (fun (control date)                  ; puts a value on it
+            (selected-date! (cast Calendar control) (parse-date date)))))
+
+;; In a view:
+(hosted calendar (.date model) Picked)
+#+END_SRC
+
+- ~(make send)~ makes the control once for its place in the view. ~send~
+  gives an output to the app, as a message that ~hosted~ makes with
+  ~on-output~. It may be called from any thread.
+- ~(put-value control value)~ is called after ~make~, and again each time the
+  view gives another value. What the control sends while it is given a value
+  is dropped, because it is not the user's.
+- ~#:width~, ~#:height~ and ~#:margin~ are set on the control, as on any
+  view. A control measures itself, as Avalonia's do.
+- Make a ~native~ once, at the top of a module. A view in the place of
+  another one is a new control.
+
 * Styles and themes
 
 [[file:docs/styles.png]]
@@ -410,6 +457,7 @@ bjo run tests/dialogs.bjo   # prints "bjogui dialogs ok"
 bjo run tests/tree.bjo      # prints "bjogui tree ok"
 bjo run tests/canvas.bjo    # prints "bjogui canvas ok"
 bjo run tests/components.bjo  # prints "bjogui components ok"
+bjo run tests/native.bjo    # prints "bjogui native ok"
 bjo run examples/counter.bjo
 bjo run examples/stopwatch.bjo
 bjo run examples/todo.bjo
@@ -424,7 +472,6 @@ bjo run examples/mixer.bjo
 - Dialogs of one's own, with a view and a state.
 - The macOS menu bar.
 - Pointer-over and pressed colours for kinds other than buttons.
-- Controls of Avalonia's or another package's that bjogui does not wrap.
 - A component asks for no size of its own: it is given one, or fills the
   space it gets. Measuring itself, an accessibility tree, and text input
   inside a component would need a subclass.