Add API for checking if there is anything being dragged onto a Response

crates/egui/src/drag_and_drop.rs

@@ -68,10 +68,21 @@ impl DragAndDrop {
     ///
     /// Returns `true` both during a drag and on the frame the pointer is released
     /// (if there is a payload).
-    pub fn has_payload<T>(ctx: &Context) -> bool
+    pub fn has_payload_of_type<T>(ctx: &Context) -> bool
     where
         T: Any + Send + Sync,
     {
         Self::payload::<T>(ctx).is_some()
     }
+
+    /// Are we carrying a payload?
+    ///
+    /// Returns `true` both during a drag and on the frame the pointer is released
+    /// (if there is a payload).
+    pub fn has_any_payload(ctx: &Context) -> bool {
+        ctx.data(|data| {
+            let state = data.get_temp::<Self>(Id::NULL);
+            state.map_or(false, |state| state.payload.is_some())
+        })
+    }
 }

crates/egui/src/response.rs

@@ -1,3 +1,5 @@
+use std::{any::Any, sync::Arc};
+
 use crate::{
     emath::{Align, Pos2, Rect, Vec2},
     menu, Context, CursorIcon, Id, LayerId, PointerButton, Sense, Ui, WidgetText,
@@ -325,6 +327,34 @@ impl Response {
         }
     }
 
+    /// Drag-and-Drop: Return what the is being held over this widget, if any.
+    ///
+    /// Only returns something if [`Self::contains_pointer`] is true,
+    /// and the user is drag-dropping something of this type.
+    pub fn drag_drop_hover_payload<T: Any + Send + Sync>(&self) -> Option<Arc<T>> {
+        // NOTE: we use `response.contains_pointer` here instead of `hovered`, because
+        // `hovered` is always false when another widget is being dragged.
+        if self.contains_pointer() {
+            crate::DragAndDrop::payload::<T>(&self.ctx)
+        } else {
+            None
+        }
+    }
+    /// Drag-and-Drop: Return what the is being dropped onto this widget, if any.
+    ///
+    /// Only returns something if [`Self::contains_pointer`] is true,
+    /// the user is drag-dropping something of this type,
+    /// and they released it this frame
+    pub fn dnd_release_payload<T: Any + Send + Sync>(&self) -> Option<Arc<T>> {
+        // NOTE: we use `response.contains_pointer` here instead of `hovered`, because
+        // `hovered` is always false when another widget is being dragged.
+        if self.contains_pointer() && self.ctx.input(|i| i.pointer.any_released()) {
+            crate::DragAndDrop::payload::<T>(&self.ctx)
+        } else {
+            None
+        }
+    }
+
     /// Where the pointer (mouse/touch) were when when this widget was clicked or dragged.
     ///
     /// `None` if the widget is not being interacted with.

crates/egui_demo_lib/src/demo/drag_and_drop.rs

@@ -38,7 +38,7 @@ pub fn drop_target<R>(
     can_accept_what_is_being_dragged: bool,
     body: impl FnOnce(&mut Ui) -> R,
 ) -> InnerResponse<R> {
-    let is_being_dragged = ui.memory(|mem| mem.is_anything_being_dragged());
+    let is_being_dragged = DragAndDrop::has_any_payload(ui.ctx());
 
     let margin = Vec2::splat(4.0);
 
@@ -128,7 +128,7 @@ impl super::View for DragAndDropDemo {
             for (col_idx, column) in self.columns.clone().into_iter().enumerate() {
                 let ui = &mut uis[col_idx];
                 let can_accept_what_is_being_dragged =
-                    DragAndDrop::has_payload::<DragInfo>(ui.ctx());
+                    DragAndDrop::has_payload_of_type::<DragInfo>(ui.ctx());
 
                 let response = drop_target(ui, can_accept_what_is_being_dragged, |ui| {
                     ui.set_min_size(vec2(64.0, 100.0));
@@ -145,13 +145,9 @@ impl super::View for DragAndDropDemo {
                 })
                 .response;
 
-                // NOTE: we use `response.contains_pointer` here instead of `hovered`, because
-                // `hovered` is always false when another widget is being dragged.
-                if response.contains_pointer() && ui.input(|i| i.pointer.any_released()) {
-                    if let Some(source) = DragAndDrop::payload::<DragInfo>(ui.ctx()) {
-                        let item = self.columns[source.col_idx].remove(source.row_idx);
-                        self.columns[col_idx].push(item);
-                    }
+                if let Some(source) = response.dnd_release_payload::<DragInfo>() {
+                    let item = self.columns[source.col_idx].remove(source.row_idx);
+                    self.columns[col_idx].push(item);
                 }
             }
         });