feat: 新增技能扩展N15一章相关示例源码

code/newsletter/N15/05_reactivity.py

@@ -0,0 +1,55 @@
+from textual.app import App
+from textual.containers import Vertical
+from textual.reactive import reactive
+from textual.widget import Widget
+from textual.widgets import Input
+
+
+class WelcomeWidget(Widget):
+    who = reactive("World!")
+    total = reactive(15)
+
+    def on_mount(self):
+        default_styles = """
+        margin: 1;
+        padding: 1;
+        """
+        self.set_styles(default_styles)
+
+    def render(self):
+        return f":partying_face: Hello, [b red]{self.who}[/]! ({self.total}/15)"
+
+    def watch_who(self, old_value, new_value):
+        self.log(
+            f"who attribute changed: old value: {old_value}, "
+            f"new value: {new_value}  "
+        )
+
+    def compute_total(self):
+        return len(self.who)
+
+
+class InputChangeApp(App):
+    def compose(self):
+        yield Vertical(
+            Input(placeholder="enter your name..."),
+            WelcomeWidget(classes="welcome"),
+        )
+
+    def on_input_changed(self, event: Input.Changed) -> None:
+        target = self.query_one(".welcome")
+        value = event.value
+
+        if len(value) > 15:
+            event.input.value = value[:15]
+            return
+
+        if not value:
+            target.who = "World!"
+        else:
+            target.who = value
+
+
+if __name__ == '__main__':
+    app = InputChangeApp()
+    app.run()