Add dnd filter example (#17)

crates/egui_dnd/examples/dnd_filter_items.rs

@@ -0,0 +1,100 @@
+use std::hash::{Hash, Hasher};
+use std::mem;
+
+use eframe::NativeOptions;
+use egui::{CentralPanel, ScrollArea, Ui};
+
+use egui_dnd::dnd;
+use egui_dnd::utils::shift_vec;
+
+/// There are two ways to filter the list:
+///
+/// 1. Just skip rendering items
+/// You will have to set the item spacing to 0 so the hidden items don't cause additional padding.
+#[allow(clippy::ptr_arg)]
+fn filter_by_skipping_items(ui: &mut Ui, filter: &str, items: &mut Vec<ItemType>) {
+    let spacing = mem::replace(&mut ui.spacing_mut().item_spacing.y, 0.0);
+
+    dnd(ui, "dnd").show_vec(items, |ui, item, handle, _dragging| {
+        if !item.number.to_string().contains(filter) {
+            return;
+        }
+        ui.spacing_mut().item_spacing.y = spacing;
+        handle.ui(ui, |ui| {
+            ui.label(&item.number.to_string());
+        });
+    });
+}
+
+/// 2. Filter the source list
+/// This is a bit more complex but will work better if you e.g.
+/// use a virtual list to improve performance with a lot of items
+#[allow(clippy::ptr_arg)]
+fn filter_by_filtering_source_list(ui: &mut Ui, filter: &str, items: &mut Vec<ItemType>) {
+    let mut filtered = items
+        .iter_mut()
+        // We enumerate so we can later get the original index
+        .enumerate()
+        .filter(|(_, item)| item.number.to_string().contains(filter))
+        .collect::<Vec<_>>();
+
+    let response = dnd(ui, "dnd").show(filtered.iter_mut(), |ui, (_, item), handle, _dragging| {
+        ui.horizontal(|ui| {
+            handle.ui(ui, |ui| {
+                ui.label(&item.number.to_string());
+            });
+        });
+    });
+
+    if let Some(update) = response.final_update() {
+        // Get the index the item had in the original vec
+        let (original_index_from, _) = filtered[update.from];
+        let (original_index_to, _) = filtered[update.to];
+        // Get the original indices of the items for the update
+        shift_vec(original_index_from, original_index_to, items);
+    }
+}
+
+struct ItemType {
+    number: u32,
+}
+
+impl Hash for ItemType {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.number.hash(state);
+    }
+}
+
+fn main() -> eframe::Result<()> {
+    let mut items: Vec<_> = (0..1000).map(|number| ItemType { number }).collect();
+
+    let mut filter = String::new();
+
+    let mut filter_type = "skip";
+
+    eframe::run_simple_native(
+        "dnd filter demo",
+        NativeOptions::default(),
+        move |ctx, _| {
+            CentralPanel::default().show(ctx, |ui| {
+                ui.horizontal(|ui| {
+                    ui.label("Filter:");
+                    ui.text_edit_singleline(&mut filter);
+
+                    ui.label("Filter type:");
+                    ui.selectable_value(&mut filter_type, "skip", "skip");
+                    ui.selectable_value(&mut filter_type, "filter", "filter");
+                });
+                ScrollArea::vertical().show(ui, |ui| {
+                    ui.set_width(ui.available_width());
+
+                    if filter_type == "skip" {
+                        filter_by_skipping_items(ui, &filter, &mut items);
+                    } else {
+                        filter_by_filtering_source_list(ui, &filter, &mut items);
+                    }
+                })
+            });
+        },
+    )
+}