Allow layout to be a list of components.

CHANGELOG.md

@@ -5,6 +5,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ## [UNRELEASED]
 
 ## Added
+
+- [#2795](https://github.com/plotly/dash/pull/2795) Allow list of components to be passed as layout.
 - [2760](https://github.com/plotly/dash/pull/2760) New additions to dcc.Loading resolving multiple issues:
   - `delay_show` and `delay_hide` props  to prevent flickering during brief loading periods (similar to Dash Bootstrap Components dbc.Spinner)
   - `overlay_style` for styling the loading overlay,  such as setting  visibility and opacity for children

dash/_validate.py

@@ -398,12 +398,13 @@ def validate_index(name, checks, index):
 
 
 def validate_layout_type(value):
-    if not isinstance(value, (Component, patch_collections_abc("Callable"))):
+    if not isinstance(
+        value, (Component, patch_collections_abc("Callable"), list, tuple)
+    ):
         raise exceptions.NoLayoutException(
             """
-            Layout must be a single dash component
+            Layout must be a single dash component, a list of dash components
             or a function that returns a dash component.
-            Cannot be a tuple (are there any trailing commas?)
             """
         )
 
@@ -418,18 +419,34 @@ def validate_layout(layout, layout_value):
             """
         )
 
-    layout_id = stringify_id(getattr(layout_value, "id", None))
+    component_ids = set()
 
-    component_ids = {layout_id} if layout_id else set()
-    for component in layout_value._traverse():  # pylint: disable=protected-access
-        component_id = stringify_id(getattr(component, "id", None))
-        if component_id and component_id in component_ids:
-            raise exceptions.DuplicateIdError(
-                f"""
-                Duplicate component id found in the initial layout: `{component_id}`
-                """
-            )
-        component_ids.add(component_id)
+    def _validate(value):
+        def _validate_id(comp):
+            component_id = stringify_id(getattr(comp, "id", None))
+            if component_id and component_id in component_ids:
+                raise exceptions.DuplicateIdError(
+                    f"""
+                    Duplicate component id found in the initial layout: `{component_id}`
+                    """
+                )
+            component_ids.add(component_id)
+
+        _validate_id(value)
+
+        for component in value._traverse():  # pylint: disable=protected-access
+            _validate_id(component)
+
+    if isinstance(layout_value, (list, tuple)):
+        for component in layout_value:
+            if isinstance(component, (Component,)):
+                _validate(component)
+            else:
+                raise exceptions.NoLayoutException(
+                    "List of components as layout must be a list of components only."
+                )
+    else:
+        _validate(layout_value)
 
 
 def validate_template(template):

dash/dash-renderer/src/APIController.react.js

@@ -21,6 +21,7 @@ import {getAppState} from './reducers/constants';
 import {STATUS} from './constants/constants';
 import {getLoadingState, getLoadingHash} from './utils/TreeContainer';
 import wait from './utils/wait';
+import isSimpleComponent from './isSimpleComponent';
 
 export const DashContext = createContext({});
 
@@ -97,20 +98,44 @@ const UnconnectedContainer = props => {
 
         content = (
             <DashContext.Provider value={provider.current}>
-                <TreeContainer
-                    _dashprivate_error={error}
-                    _dashprivate_layout={layout}
-                    _dashprivate_loadingState={getLoadingState(
-                        layout,
-                        [],
-                        loadingMap
-                    )}
-                    _dashprivate_loadingStateHash={getLoadingHash(
-                        [],
-                        loadingMap
-                    )}
-                    _dashprivate_path={JSON.stringify([])}
-                />
+                {Array.isArray(layout) ? (
+                    layout.map((c, i) =>
+                        isSimpleComponent(c) ? (
+                            c
+                        ) : (
+                            <TreeContainer
+                                _dashprivate_error={error}
+                                _dashprivate_layout={c}
+                                _dashprivate_loadingState={getLoadingState(
+                                    c,
+                                    [i],
+                                    loadingMap
+                                )}
+                                _dashprivate_loadingStateHash={getLoadingHash(
+                                    [i],
+                                    loadingMap
+                                )}
+                                _dashprivate_path={`[${i}]`}
+                                key={i}
+                            />
+                        )
+                    )
+                ) : (
+                    <TreeContainer
+                        _dashprivate_error={error}
+                        _dashprivate_layout={layout}
+                        _dashprivate_loadingState={getLoadingState(
+                            layout,
+                            [],
+                            loadingMap
+                        )}
+                        _dashprivate_loadingStateHash={getLoadingHash(
+                            [],
+                            loadingMap
+                        )}
+                        _dashprivate_path={'[]'}
+                    />
+                )}
             </DashContext.Provider>
         );
     } else {
@@ -216,7 +241,7 @@ UnconnectedContainer.propTypes = {
     graphs: PropTypes.object,
     hooks: PropTypes.object,
     layoutRequest: PropTypes.object,
-    layout: PropTypes.object,
+    layout: PropTypes.any,
     loadingMap: PropTypes.any,
     history: PropTypes.any,
     error: PropTypes.object,

tests/integration/test_integration.py

@@ -427,3 +427,87 @@ def test_inin027_multi_page_without_pages_folder(dash_duo):
     del dash.page_registry["not_found_404"]
 
     assert not dash_duo.get_logs()
+
+
+def test_inin028_layout_as_list(dash_duo):
+    app = Dash()
+
+    app.layout = [
+        html.Div("one", id="one"),
+        html.Div("two", id="two"),
+        html.Button("direct", id="direct"),
+        html.Div(id="direct-output"),
+        html.Div([html.Button("nested", id="nested"), html.Div(id="nested-output")]),
+    ]
+
+    @app.callback(
+        Output("direct-output", "children"),
+        Input("direct", "n_clicks"),
+        prevent_initial_call=True,
+    )
+    def on_direct_click(n_clicks):
+        return f"Clicked {n_clicks} times"
+
+    @app.callback(
+        Output("nested-output", "children"),
+        Input("nested", "n_clicks"),
+        prevent_initial_call=True,
+    )
+    def on_nested_click(n_clicks):
+        return f"Clicked {n_clicks} times"
+
+    dash_duo.start_server(app)
+
+    dash_duo.wait_for_text_to_equal("#one", "one")
+    dash_duo.wait_for_text_to_equal("#two", "two")
+
+    dash_duo.wait_for_element("#direct").click()
+    dash_duo.wait_for_text_to_equal("#direct-output", "Clicked 1 times")
+
+    dash_duo.wait_for_element("#nested").click()
+    dash_duo.wait_for_text_to_equal("#nested-output", "Clicked 1 times")
+
+
+def test_inin029_layout_as_list_with_pages(dash_duo):
+    app = Dash(use_pages=True, pages_folder="")
+
+    dash.register_page(
+        "list-pages",
+        "/",
+        layout=[
+            html.Div("one", id="one"),
+            html.Div("two", id="two"),
+            html.Button("direct", id="direct"),
+            html.Div(id="direct-output"),
+            html.Div(
+                [html.Button("nested", id="nested"), html.Div(id="nested-output")]
+            ),
+        ],
+    )
+
+    @app.callback(
+        Output("direct-output", "children"),
+        Input("direct", "n_clicks"),
+        prevent_initial_call=True,
+    )
+    def on_direct_click(n_clicks):
+        return f"Clicked {n_clicks} times"
+
+    @app.callback(
+        Output("nested-output", "children"),
+        Input("nested", "n_clicks"),
+        prevent_initial_call=True,
+    )
+    def on_nested_click(n_clicks):
+        return f"Clicked {n_clicks} times"
+
+    dash_duo.start_server(app)
+
+    dash_duo.wait_for_text_to_equal("#one", "one")
+    dash_duo.wait_for_text_to_equal("#two", "two")
+
+    dash_duo.wait_for_element("#direct").click()
+    dash_duo.wait_for_text_to_equal("#direct-output", "Clicked 1 times")
+
+    dash_duo.wait_for_element("#nested").click()
+    dash_duo.wait_for_text_to_equal("#nested-output", "Clicked 1 times")