Add cancel event (#4476)

* feat: add cancel event

* feat: provide cancel event

* feat: insert cancel event in web

* fix: typo

* feat: propagate implementation of cancel event

* fix merge conflicts / tests

---------

Co-authored-by: Jonathan Kelley <jkelleyrtp@gmail.com>

packages/html/src/events/cancel.rs

@@ -0,0 +1,88 @@
+use dioxus_core::Event;
+
+pub type CancelEvent = Event<CancelData>;
+
+pub struct CancelData {
+    inner: Box<dyn HasCancelData>,
+}
+
+impl<E: HasCancelData> From<E> for CancelData {
+    fn from(e: E) -> Self {
+        Self { inner: Box::new(e) }
+    }
+}
+
+impl std::fmt::Debug for CancelData {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("CancelData").finish()
+    }
+}
+
+impl PartialEq for CancelData {
+    fn eq(&self, _other: &Self) -> bool {
+        true
+    }
+}
+
+impl CancelData {
+    /// Create a new CancelData
+    pub fn new(inner: impl HasCancelData + 'static) -> Self {
+        Self {
+            inner: Box::new(inner),
+        }
+    }
+
+    /// Downcast this event to a concrete event type
+    #[inline(always)]
+    pub fn downcast<T: 'static>(&self) -> Option<&T> {
+        self.inner.as_any().downcast_ref::<T>()
+    }
+}
+
+#[cfg(feature = "serialize")]
+/// A serialized version of CancelData
+#[derive(serde::Serialize, serde::Deserialize, Debug, PartialEq, Clone)]
+pub struct SerializedCancelData {}
+
+#[cfg(feature = "serialize")]
+impl From<&CancelData> for SerializedCancelData {
+    fn from(_: &CancelData) -> Self {
+        Self {}
+    }
+}
+
+#[cfg(feature = "serialize")]
+impl HasCancelData for SerializedCancelData {
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
+}
+
+#[cfg(feature = "serialize")]
+impl serde::Serialize for CancelData {
+    fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
+        SerializedCancelData::from(self).serialize(serializer)
+    }
+}
+
+#[cfg(feature = "serialize")]
+impl<'de> serde::Deserialize<'de> for CancelData {
+    fn deserialize<D: serde::Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
+        let data = SerializedCancelData::deserialize(deserializer)?;
+        Ok(Self {
+            inner: Box::new(data),
+        })
+    }
+}
+
+pub trait HasCancelData: std::any::Any {
+    /// return self as Any
+    fn as_any(&self) -> &dyn std::any::Any;
+}
+
+impl_event! {
+    CancelData;
+
+    /// oncancel
+    oncancel
+}