Event Handling

Less than 1 minute

Event Handling

The WebCAD event system lets you listen to changes in entities, documents, commands, and more.

Online Examples

Example	Description	Link
Entity Added Event	Listen to `EntityAdded`	Online Demo{target="_blank"}
Entity Modified Event	Listen to `EntityModified`	Online Demo{target="_blank"}
Selection Changed Event	Listen to `SelectionChanged`	Online Demo{target="_blank"}
Command Events	`CommandStarted` and `CommandEnded`	Online Demo{target="_blank"}
Document Events	`DocumentOpened` and `DocumentSaved`	Online Demo{target="_blank"}

Core API

Listen to Events

const { Engine, CadEvents } = vjcad;

// Listen to entity-added event
Engine.eventManager.on(CadEvents.EntityAdded, (args) => {
    const entity = args.entity;
    console.log("Entity added:", entity.type);
});

// Listen to entity-modified event
Engine.eventManager.on(CadEvents.EntityModified, (args) => {
    console.log("Entity modified:", args.entity.id);
});

// Listen to selection-changed event
Engine.eventManager.on(CadEvents.SelectionChanged, (args) => {
    console.log("Selection changed:", args.entities.length);
});

Cancelable Events

Some events can be intercepted and canceled before the operation is executed:

// Listen to entity-adding event (cancelable)
Engine.eventManager.on(CadEvents.EntityAdding, (args) => {
    if (someCondition) {
        args.cancel = true;  // Cancel add operation
    }
});

Command Events

// Command started
Engine.eventManager.on(CadEvents.CommandStarted, (args) => {
    console.log("Command started:", args.commandName);
});

// Command ended
Engine.eventManager.on(CadEvents.CommandEnded, (args) => {
    console.log("Command ended:", args.commandName);
});

Remove Event Listeners

// Remove a specific event listener
const handler = (args) => { /* ... */ };
Engine.eventManager.on(CadEvents.EntityAdded, handler);
Engine.eventManager.off(CadEvents.EntityAdded, handler);

Common Event Types

Event	Description
`EntityAdding`	Before entity is added, cancelable
`EntityAdded`	After entity is added
`EntityModifying`	Before entity is modified, cancelable
`EntityModified`	After entity is modified
`EntityErasing`	Before entity is deleted, cancelable
`EntityErased`	After entity is deleted
`SelectionChanged`	Selection set changed
`CommandStarted`	Command started
`CommandEnded`	Command ended
`DocumentOpened`	Document opened
`DocumentSaved`	Document saved