simplify example, replace get_single to Single Query (#16187)

# Objective

clean up example get_single method, make code clean;

## Solution

- replace `Query`  with `Single` Query
- remove `get_single` or `get_single_mut` condition block

examples/2d/2d_viewport_to_world.rs

@@ -12,15 +12,11 @@ fn main() {
 
 fn draw_cursor(
     camera_query: Single<(&Camera, &GlobalTransform)>,
-    windows: Query<&Window>,
+    window: Single<&Window>,
     mut gizmos: Gizmos,
 ) {
     let (camera, camera_transform) = *camera_query;
 
-    let Ok(window) = windows.get_single() else {
-        return;
-    };
-
     let Some(cursor_position) = window.cursor_position() else {
         return;
     };

examples/3d/camera_sub_view.rs

@@ -253,13 +253,9 @@ fn move_camera_view(
 
 // To ensure viewports remain the same at any window size
 fn resize_viewports(
-    windows: Query<&Window, With<bevy::window::PrimaryWindow>>,
+    window: Single<&Window, With<bevy::window::PrimaryWindow>>,
     mut viewports: Query<(&mut Camera, &ExampleViewports)>,
 ) {
-    let Ok(window) = windows.get_single() else {
-        return;
-    };
-
     let window_size = window.physical_size();
 
     let small_height = window_size.y / 5;

examples/3d/pbr.rs

@@ -127,10 +127,9 @@ fn setup(
 fn environment_map_load_finish(
     mut commands: Commands,
     asset_server: Res<AssetServer>,
-    environment_maps: Query<&EnvironmentMapLight>,
+    environment_map: Single<&EnvironmentMapLight>,
-    label_query: Query<Entity, With<EnvironmentMapLabel>>,
+    label_entity: Single<Entity, With<EnvironmentMapLabel>>,
 ) {
-    if let Ok(environment_map) = environment_maps.get_single() {
     if asset_server
         .load_state(&environment_map.diffuse_map)
         .is_loaded()
@@ -138,10 +137,7 @@ fn environment_map_load_finish(
             .load_state(&environment_map.specular_map)
             .is_loaded()
     {
-            if let Ok(label_entity) = label_query.get_single() {
+        commands.entity(*label_entity).despawn();
-                commands.entity(label_entity).despawn();
-            }
-        }
     }
 }
 

examples/asset/alter_mesh.rs

@@ -149,13 +149,11 @@ fn spawn_text(mut commands: Commands) {
 
 fn alter_handle(
     asset_server: Res<AssetServer>,
-    mut right_shape: Query<(&mut Mesh3d, &mut Shape), Without<Left>>,
+    right_shape: Single<(&mut Mesh3d, &mut Shape), Without<Left>>,
 ) {
     // Mesh handles, like other parts of the ECS, can be queried as mutable and modified at
     // runtime. We only spawned one shape without the `Left` marker component.
-    let Ok((mut mesh, mut shape)) = right_shape.get_single_mut() else {
+    let (mut mesh, mut shape) = right_shape.into_inner();
-        return;
-    };
 
     // Switch to a new Shape variant
     shape.set_next_variant();
@@ -174,17 +172,11 @@ fn alter_handle(
 
 fn alter_mesh(
     mut is_mesh_scaled: Local<bool>,
-    left_shape: Query<&Mesh3d, With<Left>>,
+    left_shape: Single<&Mesh3d, With<Left>>,
     mut meshes: ResMut<Assets<Mesh>>,
 ) {
-    // It's convenient to retrieve the asset handle stored with the shape on the left. However,
-    // we could just as easily have retained this in a resource or a dedicated component.
-    let Ok(handle) = left_shape.get_single() else {
-        return;
-    };
-
     // Obtain a mutable reference to the Mesh asset.
-    let Some(mesh) = meshes.get_mut(handle) else {
+    let Some(mesh) = meshes.get_mut(*left_shape) else {
         return;
     };
 

examples/asset/alter_sprite.rs

@@ -107,13 +107,11 @@ fn spawn_text(mut commands: Commands) {
 
 fn alter_handle(
     asset_server: Res<AssetServer>,
-    mut right_bird: Query<(&mut Bird, &mut Sprite), Without<Left>>,
+    right_bird: Single<(&mut Bird, &mut Sprite), Without<Left>>,
 ) {
     // Image handles, like other parts of the ECS, can be queried as mutable and modified at
     // runtime. We only spawned one bird without the `Left` marker component.
-    let Ok((mut bird, mut sprite)) = right_bird.get_single_mut() else {
+    let (mut bird, mut sprite) = right_bird.into_inner();
-        return;
-    };
 
     // Switch to a new Bird variant
     bird.set_next_variant();
@@ -124,15 +122,9 @@ fn alter_handle(
     sprite.image = asset_server.load(bird.get_texture_path());
 }
 
-fn alter_asset(mut images: ResMut<Assets<Image>>, left_bird: Query<&Sprite, With<Left>>) {
+fn alter_asset(mut images: ResMut<Assets<Image>>, left_bird: Single<&Sprite, With<Left>>) {
-    // It's convenient to retrieve the asset handle stored with the bird on the left. However,
-    // we could just as easily have retained this in a resource or a dedicated component.
-    let Ok(sprite) = left_bird.get_single() else {
-        return;
-    };
-
     // Obtain a mutable reference to the Image asset.
-    let Some(image) = images.get_mut(&sprite.image) else {
+    let Some(image) = images.get_mut(&left_bird.image) else {
         return;
     };
 

examples/audio/audio_control.rs

@@ -20,32 +20,20 @@ fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
 #[derive(Component)]
 struct MyMusic;
 
-fn update_speed(music_controller: Query<&AudioSink, With<MyMusic>>, time: Res<Time>) {
+fn update_speed(sink: Single<&AudioSink, With<MyMusic>>, time: Res<Time>) {
-    if let Ok(sink) = music_controller.get_single() {
     sink.set_speed((ops::sin(time.elapsed_secs() / 5.0) + 1.0).max(0.1));
-    }
 }
 
-fn pause(
+fn pause(keyboard_input: Res<ButtonInput<KeyCode>>, sink: Single<&AudioSink, With<MyMusic>>) {
-    keyboard_input: Res<ButtonInput<KeyCode>>,
-    music_controller: Query<&AudioSink, With<MyMusic>>,
-) {
     if keyboard_input.just_pressed(KeyCode::Space) {
-        if let Ok(sink) = music_controller.get_single() {
         sink.toggle();
     }
-    }
 }
 
-fn volume(
+fn volume(keyboard_input: Res<ButtonInput<KeyCode>>, sink: Single<&AudioSink, With<MyMusic>>) {
-    keyboard_input: Res<ButtonInput<KeyCode>>,
-    music_controller: Query<&AudioSink, With<MyMusic>>,
-) {
-    if let Ok(sink) = music_controller.get_single() {
     if keyboard_input.just_pressed(KeyCode::Equal) {
         sink.set_volume(sink.volume() + 0.1);
     } else if keyboard_input.just_pressed(KeyCode::Minus) {
         sink.set_volume(sink.volume() - 0.1);
     }
-    }
 }

examples/camera/2d_top_down_camera.rs

@@ -73,18 +73,10 @@ fn setup_camera(mut commands: Commands) {
 
 /// Update the camera position by tracking the player.
 fn update_camera(
-    mut camera: Query<&mut Transform, (With<Camera2d>, Without<Player>)>,
+    mut camera: Single<&mut Transform, (With<Camera2d>, Without<Player>)>,
-    player: Query<&Transform, (With<Player>, Without<Camera2d>)>,
+    player: Single<&Transform, (With<Player>, Without<Camera2d>)>,
     time: Res<Time>,
 ) {
-    let Ok(mut camera) = camera.get_single_mut() else {
-        return;
-    };
-
-    let Ok(player) = player.get_single() else {
-        return;
-    };
-
     let Vec3 { x, y, .. } = player.translation;
     let direction = Vec3::new(x, y, camera.translation.z);
 
@@ -101,14 +93,10 @@ fn update_camera(
 ///
 /// A more robust solution for player movement can be found in `examples/movement/physics_in_fixed_timestep.rs`.
 fn move_player(
-    mut player: Query<&mut Transform, With<Player>>,
+    mut player: Single<&mut Transform, With<Player>>,
     time: Res<Time>,
     kb_input: Res<ButtonInput<KeyCode>>,
 ) {
-    let Ok(mut player) = player.get_single_mut() else {
-        return;
-    };
-
     let mut direction = Vec2::ZERO;
 
     if kb_input.pressed(KeyCode::KeyW) {

examples/camera/first_person_view_model.rs

@@ -207,11 +207,10 @@ fn spawn_text(mut commands: Commands) {
 
 fn move_player(
     accumulated_mouse_motion: Res<AccumulatedMouseMotion>,
-    mut player: Query<(&mut Transform, &CameraSensitivity), With<Player>>,
+    player: Single<(&mut Transform, &CameraSensitivity), With<Player>>,
 ) {
-    let Ok((mut transform, camera_sensitivity)) = player.get_single_mut() else {
+    let (mut transform, camera_sensitivity) = player.into_inner();
-        return;
+
-    };
     let delta = accumulated_mouse_motion.delta;
 
     if delta != Vec2::ZERO {
@@ -242,12 +241,9 @@ fn move_player(
 
 fn change_fov(
     input: Res<ButtonInput<KeyCode>>,
-    mut world_model_projection: Query<&mut Projection, With<WorldModelCamera>>,
+    mut world_model_projection: Single<&mut Projection, With<WorldModelCamera>>,
 ) {
-    let Ok(mut projection) = world_model_projection.get_single_mut() else {
+    let Projection::Perspective(ref mut perspective) = world_model_projection.as_mut() else {
-        return;
-    };
-    let Projection::Perspective(ref mut perspective) = projection.as_mut() else {
         unreachable!(
             "The `Projection` component was explicitly built with `Projection::Perspective`"
         );

examples/helpers/camera_controller.rs

@@ -109,11 +109,12 @@ fn run_camera_controller(
     key_input: Res<ButtonInput<KeyCode>>,
     mut toggle_cursor_grab: Local<bool>,
     mut mouse_cursor_grab: Local<bool>,
-    mut query: Query<(&mut Transform, &mut CameraController), With<Camera>>,
+    query: Single<(&mut Transform, &mut CameraController), With<Camera>>,
 ) {
     let dt = time.delta_secs();
 
-    if let Ok((mut transform, mut controller)) = query.get_single_mut() {
+    let (mut transform, mut controller) = query.into_inner();
+
     if !controller.initialized {
         let (yaw, pitch, _roll) = transform.rotation.to_euler(EulerRot::YXZ);
         controller.yaw = yaw;
@@ -219,8 +220,6 @@ fn run_camera_controller(
             .clamp(-PI / 2., PI / 2.);
         controller.yaw -=
             accumulated_mouse_motion.delta.x * RADIANS_PER_DOT * controller.sensitivity;
-            transform.rotation =
+        transform.rotation = Quat::from_euler(EulerRot::ZYX, 0.0, controller.yaw, controller.pitch);
-                Quat::from_euler(EulerRot::ZYX, 0.0, controller.yaw, controller.pitch);
-        }
     }
 }

examples/math/cubic_splines.rs

@@ -308,7 +308,7 @@ fn handle_mouse_press(
     mouse_position: Res<MousePosition>,
     mut edit_move: ResMut<MouseEditMove>,
     mut control_points: ResMut<ControlPoints>,
-    camera: Query<(&Camera, &GlobalTransform)>,
+    camera: Single<(&Camera, &GlobalTransform)>,
 ) {
     let Some(mouse_pos) = mouse_position.0 else {
         return;
@@ -336,9 +336,7 @@ fn handle_mouse_press(
                     continue;
                 };
 
-                let Ok((camera, camera_transform)) = camera.get_single() else {
+                let (camera, camera_transform) = *camera;
-                    continue;
-                };
 
                 // Convert the starting point and end point (current mouse pos) into world coords:
                 let Ok(point) = camera.viewport_to_world_2d(camera_transform, start) else {
@@ -365,7 +363,7 @@ fn draw_edit_move(
     edit_move: Res<MouseEditMove>,
     mouse_position: Res<MousePosition>,
     mut gizmos: Gizmos,
-    camera: Query<(&Camera, &GlobalTransform)>,
+    camera: Single<(&Camera, &GlobalTransform)>,
 ) {
     let Some(start) = edit_move.start else {
         return;
@@ -373,9 +371,8 @@ fn draw_edit_move(
     let Some(mouse_pos) = mouse_position.0 else {
         return;
     };
-    let Ok((camera, camera_transform)) = camera.get_single() else {
+
-        return;
+    let (camera, camera_transform) = *camera;
-    };
 
     // Resources store data in viewport coordinates, so we need to convert to world coordinates
     // to display them:

examples/mobile/src/lib.rs

@@ -171,12 +171,8 @@ fn setup_music(asset_server: Res<AssetServer>, mut commands: Commands) {
 // This is handled by the OS on iOS, but not on Android.
 fn handle_lifetime(
     mut lifecycle_events: EventReader<AppLifecycle>,
-    music_controller: Query<&AudioSink>,
+    music_controller: Single<&AudioSink>,
 ) {
-    let Ok(music_controller) = music_controller.get_single() else {
-        return;
-    };
-
     for event in lifecycle_events.read() {
         match event {
             AppLifecycle::Idle | AppLifecycle::WillSuspend | AppLifecycle::WillResume => {}

examples/window/screenshot.rs

@@ -32,18 +32,15 @@ fn screenshot_on_spacebar(
 fn screenshot_saving(
     mut commands: Commands,
     screenshot_saving: Query<Entity, With<Capturing>>,
-    windows: Query<Entity, With<Window>>,
+    window: Single<Entity, With<Window>>,
 ) {
-    let Ok(window) = windows.get_single() else {
-        return;
-    };
     match screenshot_saving.iter().count() {
         0 => {
-            commands.entity(window).remove::<CursorIcon>();
+            commands.entity(*window).remove::<CursorIcon>();
         }
         x if x > 0 => {
             commands
-                .entity(window)
+                .entity(*window)
                 .insert(CursorIcon::from(SystemCursorIcon::Progress));
         }
         _ => {}