Tree view¶

Usage¶

When to use¶

• Data in hierarchical form can be represented in a tree structure. Examples include directory, organization and location structures.
• Apply a tree view to large data sets that can be categorized into two or more levels.

Best practices¶

• A tree view should not have more than four sub-levels (not including the root node).
• The most commonly accessed objects should appear in the first two levels.
• Use a natural hierarchical structure that is familiar to most users. Balance discoverability with a predictable user model that minimizes confusion.
• A tree view should be supported by a breadcrumb within the content area.
• Use nodes with icons only if you have meaningful icons available.
• Don't mix nodes with icons and nodes with just a label within the same hierarchy.

Design¶

Elements¶

A tree view consists of the following elements:

1. Expand/collapse icon
2. Node icon (optional)
3. Label
4. Badge (optional)
5. Indicator (optional)
6. Node: Hover state
7. Node: Selected state
8. Checkbox and/or option box per node (optional)
9. Options menu (e.g. additional commands) (optional)

Item representation¶

The standard tree view component supports 2 different node representations:

1. Node with main-label
2. Node with main-label and sub-label

Features¶

The tree view component has the following features:

• Showing multiple trees in a list.
• Showing the trees in a flat mode with navigation/breadcrumb on top.
• Children of parent nodes are lazy loaded upon request (in case they are not yet available in the model).
• Menu support via command pattern; the commands can be set via input properties.
• Multi selection and focus support.
• Checkbox and/or option box per node.
• Virtualization support: Input properties allow to set the page size and the number of pages to be virtualized. Current limitation is roughly half a million of tree items. This is due to some strange behavior with flex containers.
• Grouped list support.
• Support of templating, if templates are present.
• Support of expand and collapse of all child elements.

Expand / collapse all¶

The tree view component supports expanding and collapsing of all child elements:

1. Expand all
2. Collapse all

Position of tree view¶

If the tree view is the main navigation of a page, then it's placed to the left.

If the tree view is part of a page then it will be represented as a card.

Note: This pattern is still work in progress and might therefore be subject to change.

Responsive behavior¶

The tree view has a default width 300px to give enough space for the labels. If the height is not enough to show all the navigation items, a scrollbar will be available.

Menu labels¶

Menu labels have to be short and concise with a maximum of two words. They share the same space with all items, like labels, icons, badges, etc. The label will be truncated at the end with 3 ..., if there is no sufficient space.

Variant¶

Showing the tree in flat mode with back-navigation on top:

In flat mode, a node also offers a third node representation format with (1) item with main-label, sub-label and value.

Code¶

Usage¶

Within a module

import { SiTreeViewModule } from '@siemens/element-ng/tree-view';

@NgModule({
  imports: [SiTreeViewModule, ...]
})

or as a standalone component

import {
  SiTreeViewComponent,
  SiTreeViewItemComponent,
  SiTreeViewItemDirective,
  SiTreeViewItemTemplateDirective
} from '@siemens/element-ng/tree-view';

@Component({
  imports: [
    SiTreeViewComponent,
    SiTreeViewItemComponent,
    SiTreeViewItemDirective,
    SiTreeViewItemTemplateDirective
  ]
})

The items property is the most important property of the si-tree-view component. It is used to provide an array of TreeItem objects to be displayed.

Note that all properties of the TreeItem interface are optional. This allows you to directly feed a JSON structure (e.g. from an API) to the tree view.

Expand/Collapse¶

Expand and collapsing of all nodes can be enabled via the expandCollapseAll property.

Dynamic Context Menu¶

The context menu can be dynamically constructed using the MenuItemsProvider.

Custom Templates¶

The tree also supports custom templates for tree items. The TreeItem object model supports the property templateName to apply a custom template.

As you can see in the example below, you can create a ng-template structured as follows where the templateName of the model has to match the siTreeViewItemTemplate value:

<ng-template let-item siTreeViewItemTemplate="yourTemplateName">
  <!-- your template -->
</ng-template>

The following example demonstrates the use of two templates to render the root and child nodes differently.

Adding, removing, updating tree items¶

Due to the way change detection works, mutations on the tree item structure assigned to the items property might not be detected by the tree view. Thus, the UI will not reflect the changes in the model.

Depending on the use case, there are different ways to trigger the change detection mechanism of the tree view:

• Create and assign a new reference, e.g. this.items = [...this.items];
• Call refresh() function on the tree component
• Use addChildItems() function on the tree component

Note: If items should be lazy-loaded when expanding a parent, consider using the loadChildren event which allows to append children while properly handling change detection.

The following example shows how to use addChildItems() to dynamically add tree items as root elements or as children of an existing tree item:

@Component({
  selector: "app-sample",
  template: `
    <button type="button" class="btn btn-primary" (click)="addItemToRoot()">
      Add item to Root
    </button>
    <button type="button" class="btn btn-primary" (click)="addItemToCompany1()">
      Add item to Company1
    </button>
    <si-tree-view class="vh-100" [items]="items"></si-tree-view>
  `,
  imports: [SiTreeViewModule],
  changeDetection: ChangeDetectionStrategy.OnPush,
  standalone: true
})
export class SampleComponent {
  @ViewChild(SiTreeViewComponent, { static: true })
  private treeViewComponent!: SiTreeViewComponent;
  private count = 0;
  protected items: TreeItem[] = [{ label: "Company1" }];

  protected addItemToRoot() {
    this.treeViewComponent.addChildItems([
      { label: `new root item ${++this.count}`, state: "leaf" }
    ]);
  }

  protected addItemToCompany1() {
    this.treeViewComponent.addChildItems(
      [{ label: `new root item ${++this.count}`, state: "leaf" }],
      this.items[0]
    );
  }
}

Playground with various options¶