Communicating between LiveViews on the same page

The post lays out several ways to make LiveViews on the same page communicate. It first suggests checking whether multiple LiveViews are needed at all, since a single LiveView with components may fit better. When multiple LiveViews are used, the examples show message passing between parent and child, between siblings through a shared ancestor, and through PubSub when the LiveViews share a root or a page identifier.

Reading notes

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• A parent LiveView can pass session data to a child LiveView with live_render, but the data is only sent when the child mounts.
• Including an assign in the child ID makes the child remount when that value changes, but remounting resets the child’s state.
• A child LiveView can send a message to its parent because the socket exposes parent_pid; root_pid is also available for deeper nesting.
• To let a parent send to a child, the child can send its own PID to the parent during connected mount, and the parent can store it in assigns.
• If two sibling LiveViews share an ancestor, one child can send a payload to the ancestor, and the ancestor can forward it to the other child.
• PubSub can be used for communication across LiveViews on the same page when they share a root LiveView.
• The post uses root_pid in the PubSub topic so subscriptions are scoped to the current page.
• The sender can use broadcast_from!/5 so it does not receive its own broadcast.
• A process registry is mentioned as an alternative, but the post warns against it because atom names are not garbage collected and it only works on the local node.
• If a user ID or session ID is used with PubSub, all tabs or windows for that user would be affected, not only one page.
• A unique page ID can be generated in the controller and passed into both LiveViews so PubSub targets only the current page.