Layout canonici

Canonical layouts are proven, versatile layouts that provide an optimal user experience on a variety of form factors.

The canonical layouts support small screen phones as well as tablets, foldables, and ChromeOS devices. Derived from Material Design guidance, the layouts are aesthetic as well as functional.

The Android framework includes specialized components that make implementation of the layouts straightforward and reliable.

The canonical layouts create engaging, productivity‑enhancing UIs that form the foundation of great apps.

List-detail

The list-detail layout enables users to explore lists of items that have descriptive, explanatory, or other supplementary information—the item detail.

The layout divides the app window into two side-by-side panes: one for the list, one for the detail. Users select items from the list to display the item detail. Deep links in the detail reveal additional content in the detail pane.

Expanded-width displays (see Use window size classes) accommodate both the list and detail at the same time. Selection of a list item updates the detail pane to show the related content for the selected item.

Medium- and compact-width displays show either the list or the detail, depending on user interaction with the app. When just the list is visible, selection of a list item displays the detail in place of the list. When just the detail is visible, pressing the back button redisplays the list.

Configuration changes such as device orientation changes or app window size changes can change the display's window size class. A list‑detail layout responds accordingly, preserving app state:

• If an expanded-width display showing both the list and detail panes narrows to medium or compact, the detail pane remains visible and the list pane is hidden
• If a medium- or compact-width display has just the detail pane visible and the window size class widens to expanded, the list and detail are shown together, and the list indicates that the item corresponding to the content in the detail pane is selected
• If a medium- or compact-width display has just the list pane visible and widens to expanded, the list and a placeholder detail pane are shown together

List-detail is ideal for messaging apps, contact managers, file browsers, or any app where the content can be organized as a list of items that reveal additional information.

Figure 1. Messaging app showing a list of conversations and the details of a selected conversation.

Implementation

The declarative paradigm of Compose supports window size class logic that determines whether to show the list and detail panes at the same time (when the width window size class is expanded) or just the list or detail pane (when the width window size class is medium or compact).

To ensure unidirectional data flow, hoist all state, including current window size class and detail of the selected list item (if any), so all composables have access to the data and can render correctly.

When showing just the detail pane on small window sizes, add a BackHandler to remove the detail pane and display just the list pane. The BackHandler is not part of the overall app navigation since the handler is dependent on the window size class and selected detail state.

For an example implementation, see the List-detail with Compose sample.

Feed

A feed layout arranges equivalent content elements in a configurable grid for quick, convenient viewing of a large amount of content.

Size and position establish relationships among the content elements.

Content groups are created by making elements the same size and positioning them together. Attention is drawn to elements by making them larger than nearby elements.

Cards and lists are common components of feed layouts.

A feed layout supports displays of almost any size because the grid can adapt from a single, scrolling column to a multi‑column scrolling feed of content.

Feeds are especially well suited for news and social media apps.

Figure 2. Social media app showing posts in cards of varying sizes.

Implementation

Feed 包含大量内容元素，这些内容元素位于一个纵向滚动容器中，而该容器采用网格布局。延迟列表可高效地在列或行中呈现大量的项。延迟网格以网格形式呈现项，支持配置项的大小和 span。

根据可用的显示区域配置网格布局的列，以设置网格项允许的最小宽度。定义网格项时，只需调整列 span 即可让某些项比其他项更为醒目。

对于部分标题、分隔线或要占据 Feed 的整个宽度的其他项，请使用 maxLineSpan 占据布局的整个宽度。

如果较小宽度的显示屏没有足够的空间来显示一个以上的列，LazyVerticalGrid 就会像 LazyColumn 一样运行。

如需查看示例实现，请参阅使用 Compose 构建 Feed 示例。

Supporting pane

Supporting pane layout organizes app content into primary and secondary display areas.

The primary display area occupies the majority of the app window (typically about two thirds) and contains the main content. The secondary display area is a pane that takes up the remainder of the app window and presents content that supports the main content.

Supporting pane layouts work well on expanded-width displays (see Use window size classes) in landscape orientation. Medium- or compact‑width displays support showing both the primary and secondary display areas if the content is adaptable to narrower display spaces, or if the additional content can be initially hidden in a bottom or side sheet accessible by means of a control such as a menu or button.

A supporting pane layout differs from a list‑detail layout in the relationship of the primary and secondary content. Secondary pane content is meaningful only in relation to the primary content; for example, a supporting pane tool window is irrelevant by itself. The supplementary content in the detail pane of a list‑detail layout, however, is meaningful even without the primary content, for example, the description of a product from a product listing.

Use cases for supporting pane include:

• Productivity apps: A document or spreadsheet accompanied by reviewer comments in a supporting pane
• Media apps: A streaming video complemented by a list of related videos in a supporting pane, or the depiction of an album of music supplemented with a playlist
• Search and reference apps: A query input form with results in a supporting pane

Figure 3. Shopping app with product descriptions in a supporting pane.

Implementation

Compose supports window size class logic, which enables you to determine whether to show both the main content and the supporting content at the same time or place the supporting content in an alternative location.

Hoist all state, including current window size class and information related to the data in the main content and supporting content.

For compact-width displays, place the supporting content below the main content or inside a bottom sheet. For medium and expanded widths, place the supporting content next to the main content, sized appropriately based on the content and space available. For medium width, split the display space equally between the main and supporting content. For expanded width, give 70% of the space to the main content, 30% to the supporting content.

For an example implementation, see the Supporting pane with Compose sample.

Additional resources

• Material Design — Canonical layouts