event docs

docs/examples/events/custom01.py

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+from textual.app import App, ComposeResult
+from textual.color import Color
+from textual.message import Message, MessageTarget
+from textual.widgets import Static
+
+
+class ColorButton(Static):
+    """A color button."""
+
+    class Selected(Message):
+        """Color selected message."""
+
+        def __init__(self, sender: MessageTarget, color: Color) -> None:
+            self.color = color
+            super().__init__(sender)
+
+    def __init__(self, color: Color) -> None:
+        self.color = color
+        super().__init__()
+
+    def on_mount(self) -> None:
+        self.styles.margin = (1, 2)
+        self.styles.content_align = ("center", "middle")
+        self.styles.background = Color.parse("#ffffff33")
+        self.styles.border = ("tall", self.color)
+
+    async def on_click(self) -> None:
+        # The emit method sends an event to a widget's parent
+        await self.emit(self.Selected(self, self.color))
+
+    def render(self) -> str:
+        return str(self.color)
+
+
+class ColorApp(App):
+    def compose(self) -> ComposeResult:
+        yield ColorButton(Color.parse("#008080"))
+        yield ColorButton(Color.parse("#808000"))
+        yield ColorButton(Color.parse("#E9967A"))
+        yield ColorButton(Color.parse("#121212"))
+
+    def on_color_button_selected(self, message: ColorButton.Selected) -> None:
+        self.screen.styles.animate("background", message.color, duration=0.5)
+
+
+app = ColorApp()
+if __name__ == "__main__":
+    app.run()