Eclipse Theia技术揭秘——自定义布局

更多内容可以查看专题https://codeteenager.github.io/theia-analysis/

在上篇文章 脚手架源码分析 文章中，我们分析了启动过程中前端页面是如何展示的，那么本篇文章我们介绍一下theia布局的相关内容以及如何自定义布局。

PhosphorJS

Theia的组件和布局系统是使用PhosphorJS实现的，PhosphorJS提供了一组丰富的组件、布局、事件和数据结构。这些使开发人员能够构建高质量的、类桌面的 Web 应用程序。Theia为什么要用PhosphorJS作为布局系统呢？在IDE 应用程序中的选项卡式和停靠式面板，这些类型的交互必须使用 JavaScript 实现，并且以可扩展且优雅的方式实现动态添加数量的模式，这就包括消息传递、调整大小/附加/分离/显示/隐藏事件、大小约束聚合和高效布局计算。PhosphorJS 以一种灵活、独立且与现有代码兼容的方式提供了这些目前在web上缺少的能力。

Github地址：https://github.com/phosphorjs/phosphor，文档地址：http://phosphorjs.github.io/。不过PhosphorJS 作者退休，项目已归档，该项目现在被 Jupyter 团队重命名为 jupyterlab/lumino，Github地址为：https://github.com/jupyterlab/lumino 。

如何实现的？

• PhosphorJS提供了一个简单而灵活的小部件类，它为消息传递和DOM节点操作建立了层次结构。这允许在整个层次结构中传播各种消息，例如：调整大小、附加、分离、显示和隐藏（以及其他功能）
• 一旦建立了可靠传播的调整大小消息，就有可能在JavaScript中实现布局，这是单独使用CSS无法实现的。通过以绝对值明确指定节点的位置和大小，浏览器能够优化回流，使其包含在页面的受影响部分中。这意味着对应用程序一部分的更改不会导致整个页面的回流成本。
• PhosphorJS认识到CSS在很多方面都很好，并且不会阻止开发人员在适当的时候使用它。PhosphorJS布局与标准CSS布局配合得很好，两者可以在小部件层次结构中自由混合。
• PhosphorJS认识到开发人员最喜欢的框架非常适合特定任务。Phosphor Widget实例可以托管由任何其他框架生成的DOM内容，并且这样的可以自由嵌Widget入任何Phosphor Widget层次结构中。
• PhosphorJS提供了大量预定义的小部件和布局，这些部件和布局很难正确有效地实现，例如：菜单和菜单栏、拆分面板、选项卡和停靠面板。这使得创建前面描述的富桌面风格应用程序变得简单。

@phosphor/widgets提供了很多布局和组件：

• BoxLayout
• BoxPanel
• DockLayout
• DockPanel
• Menu
• MenuBar
• Panel
• PanelLayout
• TabBar

其中像BoxLayout、DockLayout都是继承layout，像BoxPanel、MenuBar、TabBar等都是继承Widget。Widget有诸多的生命周期回调函数：

• onActivateRequest
• onBeforeShow
• onAfterShow
• onBeforeHide
• onAfterHide
• onBeforeAttach
• onAfterAttach
• onBeforeDetach
• onAfterDetach
• onChildAdded
• onChildRemoved
• onCloseRequest
• onResize
• onUpdateRequest
• onFitRequest

通过attach方法，将widget插入到dom节点中。attach实现如下：

//@phosphor/widgets/src/widget.ts
 
export
 function attach(widget: Widget, host: HTMLElement, ref: HTMLElement | null = null): void {
    if (widget.parent) {
      throw new Error('Cannot attach a child widget.');
    }
    if (widget.isAttached || document.body.contains(widget.node)) {
      throw new Error('Widget is already attached.');
    }
    if (!document.body.contains(host)) {
      throw new Error('Host is not attached.');
    }
    MessageLoop.sendMessage(widget, Widget.Msg.BeforeAttach);
    host.insertBefore(widget.node, ref);
    MessageLoop.sendMessage(widget, Widget.Msg.AfterAttach);
  }

最终调用host.insertBefore插入到ref节点前。

在之前脚手架分析中，我们最后看到FrontendApplication的start方法启动主要做了这样几件事：1、初始化并启动frontend application contributions，2、调用@phosphor/widgets的Widget.attach方法，将ApplicationShell布局插入到document.body中class为theia-preload的节点前，3、初始化ApplicationShell的布局，4、隐藏启动动画，展示页面。

//@theia/core/src/browser/frontend-application.ts 

get shell(): ApplicationShell {
        return this._shell;
}
protected attachShell(host: HTMLElement): void {
        const ref = this.getStartupIndicator(host);
        Widget.attach(this.shell, host, ref);
}

其中shell是ApplicationShell，接下来具体介绍一下ApplicationShell。

ApplicationShell

Theia整个视图布局主要包括topPanel、leftPanel、mainPanel、rightPanel、bottomPanel和statusBar。

ApplicationShell继承了Widget，在ApplicationShell中分别定义了以上几个视图，在createLayout方法中使用@phosphor/widgets提供的布局容器进行组装。

//@theia/core/src/browser/shell/application-shell.ts

@injectable()
export class ApplicationShell extends Widget {
    /**
     * The dock panel in the main shell area. This is where editors usually go to.
     */
    mainPanel: TheiaDockPanel;

    /**
     * The dock panel in the bottom shell area. In contrast to the main panel, the bottom panel
     * can be collapsed and expanded.
     */
    bottomPanel: TheiaDockPanel;

    /**
     * Handler for the left side panel. The primary application views go here, such as the
     * file explorer and the git view.
     */
    leftPanelHandler: SidePanelHandler;

    /**
     * Handler for the right side panel. The secondary application views go here, such as the
     * outline view.
     */
    rightPanelHandler: SidePanelHandler;

    /**
     * General options for the application shell.
     */
    protected options: ApplicationShell.Options;

    /**
     * The fixed-size panel shown on top. This one usually holds the main menu.
     */
    topPanel: Panel;

    protected initializeShell(): void {
        this.addClass(APPLICATION_SHELL_CLASS);
        this.id = 'theia-app-shell';
        // Merge the user-defined application options with the default options
        this.options = {
            bottomPanel: {
                ...ApplicationShell.DEFAULT_OPTIONS.bottomPanel,
                ...this.options?.bottomPanel || {}
            },
            leftPanel: {
                ...ApplicationShell.DEFAULT_OPTIONS.leftPanel,
                ...this.options?.leftPanel || {}
            },
            rightPanel: {
                ...ApplicationShell.DEFAULT_OPTIONS.rightPanel,
                ...this.options?.rightPanel || {}
            }
        };

        this.mainPanel = this.createMainPanel();
        this.topPanel = this.createTopPanel();
        this.bottomPanel = this.createBottomPanel();

        this.leftPanelHandler = this.sidePanelHandlerFactory();
        this.leftPanelHandler.create('left', this.options.leftPanel);
        this.leftPanelHandler.dockPanel.widgetAdded.connect((_, widget) => this.fireDidAddWidget(widget));
        this.leftPanelHandler.dockPanel.widgetRemoved.connect((_, widget) => this.fireDidRemoveWidget(widget));

        this.rightPanelHandler = this.sidePanelHandlerFactory();
        this.rightPanelHandler.create('right', this.options.rightPanel);
        this.rightPanelHandler.dockPanel.widgetAdded.connect((_, widget) => this.fireDidAddWidget(widget));
        this.rightPanelHandler.dockPanel.widgetRemoved.connect((_, widget) => this.fireDidRemoveWidget(widget));

        this.layout = this.createLayout();

        this.tracker.currentChanged.connect(this.onCurrentChanged, this);
        this.tracker.activeChanged.connect(this.onActiveChanged, this);
}

    /**
     * Assemble the application shell layout. Override this method in order to change the arrangement
     * of the main area and the side panels.
     */
    protected createLayout(): Layout {
        const bottomSplitLayout = this.createSplitLayout(
            [this.mainPanel, this.bottomPanel],
            [1, 0],
            { orientation: 'vertical', spacing: 0 }
        );
        const panelForBottomArea = new SplitPanel({ layout: bottomSplitLayout });
        panelForBottomArea.id = 'theia-bottom-split-panel';

        const leftRightSplitLayout = this.createSplitLayout(
            [this.leftPanelHandler.container, panelForBottomArea, this.rightPanelHandler.container],
            [0, 1, 0],
            { orientation: 'horizontal', spacing: 0 }
        );
        const panelForSideAreas = new SplitPanel({ layout: leftRightSplitLayout });
        panelForSideAreas.id = 'theia-left-right-split-panel';

        return this.createBoxLayout(
            [this.topPanel, panelForSideAreas, this.statusBar],
            [0, 1, 0],
            { direction: 'top-to-bottom', spacing: 0 }
        );
    }
}

自定义布局

以上介绍了ApplicationShell的组成和布局，那么我们要扩展一个toolbar或者simulator也就简单了，只需重写ApplicationShell的createLayout方法，添加自己定义的视图，然后使用inversify重新绑定即可。其实官方提供了一个@theia/toolbar的模块，也是按上述的方法去重写的。效果如图：

代码如下：

@injectable()
export class ApplicationShellWithToolbarOverride extends ApplicationShell {
    @inject(ToolbarPreferences) protected toolbarPreferences: ToolbarPreferences;
    @inject(PreferenceService) protected readonly preferenceService: PreferenceService;
    @inject(ToolbarFactory) protected readonly toolbarFactory: () => Toolbar;

    protected toolbar: Toolbar;

    @postConstruct()
    protected override async init(): Promise<void> {
        this.toolbar = this.toolbarFactory();
        this.toolbar.id = 'main-toolbar';
        super.init();
        await this.toolbarPreferences.ready;
        this.tryShowToolbar();
        this.mainPanel.onDidToggleMaximized(() => {
            this.tryShowToolbar();
        });
        this.bottomPanel.onDidToggleMaximized(() => {
            this.tryShowToolbar();
        });
        this.preferenceService.onPreferenceChanged(event => {
            if (event.preferenceName === TOOLBAR_ENABLE_PREFERENCE_ID) {
                this.tryShowToolbar();
            }
        });
    }

    protected tryShowToolbar(): boolean {
        const doShowToolbarFromPreference = this.toolbarPreferences[TOOLBAR_ENABLE_PREFERENCE_ID];
        const isShellMaximized = this.mainPanel.hasClass(MAXIMIZED_CLASS) || this.bottomPanel.hasClass(MAXIMIZED_CLASS);
        if (doShowToolbarFromPreference && !isShellMaximized) {
            this.toolbar.show();
            return true;
        }
        this.toolbar.hide();
        return false;
    }

    protected override createLayout(): Layout {
        const bottomSplitLayout = this.createSplitLayout(
            [this.mainPanel, this.bottomPanel],
            [1, 0],
            { orientation: 'vertical', spacing: 0 },
        );
        const panelForBottomArea = new SplitPanel({ layout: bottomSplitLayout });
        panelForBottomArea.id = 'theia-bottom-split-panel';

        const leftRightSplitLayout = this.createSplitLayout(
            [this.leftPanelHandler.container, panelForBottomArea, this.rightPanelHandler.container],
            [0, 1, 0],
            { orientation: 'horizontal', spacing: 0 },
        );
        const panelForSideAreas = new SplitPanel({ layout: leftRightSplitLayout });
        panelForSideAreas.id = 'theia-left-right-split-panel';
        return this.createBoxLayout(
            [this.topPanel, this.toolbar, panelForSideAreas, this.statusBar],
            [0, 0, 1, 0],
            { direction: 'top-to-bottom', spacing: 0 },
        );
    }
}

export const bindToolbarApplicationShell = (bind: interfaces.Bind, rebind: interfaces.Rebind, unbind: interfaces.Unbind): void => {
    bind(ApplicationShellWithToolbarOverride).toSelf().inSingletonScope();
    rebind(ApplicationShell).toService(ApplicationShellWithToolbarOverride);
};

定义了ApplicationShellWithToolbarOverride继承自ApplicationShell，然后创建toolbar，并在createLayout方法中将toolbar添加进去，最后将ApplicationShellWithToolbarOverride绑定到容器中，然后通过rebind替换掉ApplicationShell即可。

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