FlexLayout

FlexLayout is a layout manager supporting multiple TabSets with draggable+resizable tabs.

This is a feature-fork of FlexLayout by Caplin. The original project hasn't been updated in some time, so this fork includes bug fixes, performance improvements, and new features like OptimizedLayout.

To install: yarn add @aptre/flex-layout

FlexLayout's only dependency is React.

Features:

• splitters
• tabs
• tab dragging and ordering
• tab set dragging (move all the tabs in a tab set in one operation)
• dock to tab set or edge of frame
• maximize tab set (double click tab set header or use icon)
• tab overflow (show menu when tabs overflow, scroll tabs using mouse wheel)
• border tab sets
• popout tabs into new browser windows
• submodels, allow layouts inside layouts
• tab renaming (double click tab text to rename)
• theming - light, underline, gray, round and dark
• works on mobile devices (iPad, Android)
• add tabs using drag, add to active tab set, add to tab set by id
• tab and tab set attributes: enableTabStrip, enableDock, enableDrop...
• customizable tabs and tab set rendering
• component state is preserved when tabs are moved
• typescript type declarations
• OptimizedLayout - renders tab content outside FlexLayout's DOM for better performance

Demo

To demo and test this library, clone this repo, then:

npm i -g yarn
yarn
yarn test:browser

Your browser will open to show + all the tests with vitest Browser Mode.

Installation

FlexLayout is in the npm repository. install using:

npm install @aptre/flex-layout

Import FlexLayout in your modules:

import {Layout, Model} from '@aptre/flex-layout';

Include the light, underline, gray or dark theme by either:

Adding an additional import:

import '@aptre/flex-layout/style/light.css';

or by adding the css to your html:

<link rel="stylesheet" href="node_modules/@aptre/flex-layout/style/light.css" />

Usage

The <Layout> component renders the tab sets and splitters, it takes the following props:

Required props:

Prop	Description
model	the layout model
factory	a factory function for creating React components

Additional optional props

The model is tree of Node objects that define the structure of the layout.

The factory is a function that takes a Node object and returns a React component that should be hosted by a tab in the layout.

The model can be created using the Model.fromJson(jsonObject) static method, and can be saved using the model.toJson() method.

Example Configuration:

var json = {
    global: {},
    borders: [],
    layout: {
        type: "row",
        weight: 100,
        children: [
            {
                type: "tabset",
                weight: 50,
                children: [
                    {
                        type: "tab",
                        name: "One",
                        component: "button",
                    },
                ],
            },
            {
                type: "tabset",
                weight: 50,
                children: [
                    {
                        type: "tab",
                        name: "Two",
                        component: "button",
                    },
                ],
            },
        ],
    },
};

Example Code

const model = Model.fromJson(json);

function App() {
    const factory = (node) => {
        var component = node.getComponent();

        if (component === "button") {
            return <button>{node.getName()}</button>;
        }
    };

    return <Layout model={model} factory={factory} />;
}

The above code would render two tab sets horizontally each containing a single tab that hosts a button component. The tabs could be moved and resized by dragging and dropping. Additional grids could be added to the layout by sending actions to the model.

OptimizedLayout

OptimizedLayout is a wrapper around Layout that renders tab content outside of FlexLayout's DOM structure for better performance. This is particularly useful for complex tab content that shouldn't re-render when the layout model changes.

Key Benefits

1. No re-renders on layout changes - Tab components are NOT re-rendered when the Model changes
2. State preservation - Tab state (scroll position, form inputs, etc.) is preserved across layout mutations
3. CSS-only updates - Only CSS properties change when layout changes, avoiding React re-renders

How It Works

1. OptimizedLayout renders Layout with lightweight TabRef placeholders instead of actual tab content
2. TabRef components listen to resize/visibility events from TabNodes
3. A sibling TabContainer renders the actual tab content with absolute positioning
4. During drag operations, TabContainer uses pointer-events: none to prevent interfering with FlexLayout's drag overlay

Example Usage

import { Model, OptimizedLayout } from "@aptre/flex-layout";
import "@aptre/flex-layout/style/light.css";

const json = {
    global: {},
    borders: [],
    layout: {
        type: "row",
        weight: 100,
        children: [
            {
                type: "tabset",
                weight: 50,
                children: [{ type: "tab", name: "Editor", component: "editor" }],
            },
            {
                type: "tabset",
                weight: 50,
                children: [{ type: "tab", name: "Preview", component: "preview" }],
            },
        ],
    },
};

const model = Model.fromJson(json);

function App() {
    // renderTab receives a TabNode and returns the content for that tab
    const renderTab = (node) => {
        const component = node.getComponent();

        if (component === "editor") {
            return <Editor />;
        }
        if (component === "preview") {
            return <Preview />;
        }
        return <div>Unknown component: {component}</div>;
    };

    return (
        <div style={{ position: "relative", width: "100%", height: "100vh" }}>
            <OptimizedLayout model={model} renderTab={renderTab} />
        </div>
    );
}

Props

OptimizedLayout accepts all the same props as Layout, except:

• renderTab (required) - Replaces factory. A function that receives a TabNode and returns a React element to render as the tab content.

All other Layout props (model, onModelChange, classNameMapper, etc.) work the same way.

When to Use OptimizedLayout

Use OptimizedLayout when:

• Your tab content is expensive to render
• You need to preserve internal component state across layout changes
• You have many tabs and want to minimize re-renders

Use the standard Layout when:

• You need tab content to re-render when the model changes
• Your tab content is simple and lightweight
• You need the factory pattern for lazy loading components

Model JSON Structure

The model json contains 4 top level elements:

• global - (optional) where global options are defined
• layout - where the main row/tabset/tabs layout hierarchy is defined
• borders - (optional) where up to 4 borders are defined ("top", "bottom", "left", "right").
• popouts - (optional) where the popout windows are defined

The layout element is built up using 3 types of 'node':

• row - rows contains a list of tabsets and child rows, the top level 'row' will render horizontally (unless the global attribute rootOrientationVertical is set) , child 'rows' will render in the opposite orientation to their parent row.

• tabset - tabsets contain a list of tabs and the index of the selected tab

• tab - tabs specify the name of the component that they should host (that will be loaded via the factory) and the text of the actual tab.

The layout structure is defined with rows within rows that contain tabsets that themselves contain tabs.

The optional borders element is made up of border nodes

• border - borders contain a list of tabs and the index of the selected tab, they can only be used in the borders top level element.

The tree structure for the JSON model is well defined as Typescript interfaces, see JSON Model

Each type of node has a defined set of requires/optional attributes.

Weights on rows and tabsets specify the relative weight of these nodes within the parent row, the actual values do not matter just their relative values (ie two tabsets of weights 30,70 would render the same if they had weights of 3,7).

By changing global or node attributes you can change the layout appearance and functionality, for example:

Setting tabSetEnableTabStrip:false in the global options would change the layout into a multi-splitter (without tabs or drag and drop).

 global: {tabSetEnableTabStrip:false},

Model Actions

Once the model json has been loaded all changes to the model are applied through actions.

You apply actions using the Model.doAction() method.

This method takes a single argument, created by one of the action generators (typically accessed as FlexLayout.Actions.<actionName>).

See Actions.ts for available actions.

Examples

model.doAction(
    FlexLayout.Actions.updateModelAttributes({
        splitterSize: 40,
    }),
);

The above example would increase the size of the splitters, this could be used to make adjusting the layout easier on a small device.

model.doAction(FlexLayout.Actions.addNode({ type: "tab", component: "grid", name: "a grid", id: "5" }, "1", FlexLayout.DockLocation.CENTER, 0));

This example adds a new grid component to the center of tabset with id "1" and at the 0'th tab position (use value -1 to add to the end of the tabs).

Note: you can get the id of a node (e.g., the node returned by the addNode action) using the method node.getId(). If an id wasn't assigned when the node was created, then one will be created for you of the form #<uuid> (e.g. #0c459064-8dee-444e-8636-eb9ab910fb27).

Note: You can intercept actions resulting from GUI changes before they are applied by implementing the onAction callback property of the Layout.

Optional Layout Props

There are many optional properties that can be applied to the layout. See ILayoutProps in Layout.tsx for the full interface.

JSON Model Definition

The JSON model is well defined as a set of TypeScript interfaces. See IJsonModel.ts for all available attributes:

• IJsonModel - Top-level model structure
• IGlobalAttributes - Global config attributes
• IJsonRowNode - Row config attributes
• IJsonTabSetNode - Tab set config attributes (note: tab sets are dynamically created as tabs are moved, and deleted when empty unless enableDeleteWhenEmpty is false)
• IJsonTabNode - Tab config attributes
• IJsonBorderNode - Border config attributes

Layout Component Methods to Create New Tabs

There are methods on the Layout Component for adding tabs. See Layout.tsx for available methods.

Example:

layoutRef.current.addTabToTabSet("NAVIGATION", {type:"tab", component:"grid", name:"a grid"});

This would add a new grid component to the tab set with id "NAVIGATION" (where layoutRef is a ref to the Layout element, see https://reactjs.org/docs/refs-and-the-dom.html ).

Tab Node Events

You can handle events on nodes by adding a listener, this would typically be done when the component is mounted in a useEffect method:

Example:

    function MyComponent({node}) {

      useEffect(() => {
        // save subject in flexlayout node tree
        node.setEventListener("save", () => {
             node.getConfig().subject = subject;
           };
        }, []);
    }

Event	parameters	Description
resize	{rect}	called when tab is resized during layout, called before it is rendered with the new size
close	none	called when a tab is closed
visibility	{visible}	called when the visibility of a tab changes
save	none	called before a tabnode is serialized to json, use to save node config by adding data to the object returned by node.getConfig()

Popout Windows

Tabs can be rendered into external browser windows (for use in multi-monitor setups) by configuring them with the enablePopout attribute. When this attribute is present an additional icon is shown in the tab header bar allowing the tab to be popped out into an external window.

For popouts to work there needs to be an additional html page 'popout.html' hosted at the same location as the main page (copy the one from examples/demo). The popout.html is the host page for the popped out tab, the styles from the main page will be copied into it at runtime.

Because popouts are rendering into a different document to the main layout any code in the popped out tab that uses the global document or window objects for event listeners will not work correctly (for example custom popup menus where the code uses document.addEventListener(...)), they need to instead use the document/window of the popout. To get the document/window of the popout use the following method on one of the elements rendered in the popout (for example a ref or target in an event handler):

    const currentDocument = selfRef.current.ownerDocument;
    const currentWindow = currentDocument.defaultView!;

In the above code selfRef is a React ref to the toplevel element in the tab being rendered.

Note: libraries may support popout windows by allowing you to specify the document to use, for example see the getDocument() callback in agGrid at https://www.ag-grid.com/javascript-grid-callbacks/

Limitations of Popouts

• FlexLayout uses React Portals to draw the popout window content, this means all the code runs in the main Window's JS context, so effectively the popout windows are just extensions of the area on which the main window can render panels.

• Your code must use the popout window/document in popout windows when adding event listeners (e.g popoutDocument.addEventListener(...)).

• Timers throttle when main window is in the background you could implement a webworker timer replacement if needed (which will not throttle)

• Many third party controls will use the global document for some event listeners, these will not work correctly without modification

• Some third party controls will suspend when the global document is hidden you can use the tab overlay attribute to 'gray out' these tabs when the main window is hidden

• Resize observers may be throttled (or stay attached to the main window), so you may need to use some other way to resize the component when in a popout (see aggrid component in demo).

• Popouts will not size and position correctly when the browser is zoomed (ie set to 50% zoom)

• Popouts cannot reload in maximized or minimized states

• by default flexlayout will maintain react state when moving tabs between windows, but you can use the enableWindowReMount tab attribute to force the component to re-mount.

See this article about using React portals in this way: https://dev.to/noriste/the-challenges-of-rendering-an-openlayers-map-in-a-popup-through-react-2elh

Alternative Layout Managers

Name	Repository
rc-dock	https://github.com/ticlo/rc-dock
Dockview	https://dockview.dev/
lumino	https://github.com/jupyterlab/lumino
golden-layout	https://github.com/golden-layout/golden-layout
react-mosaic	https://github.com/nomcopter/react-mosaic