When a window is refreshed or restored from a previous session, the view and its associated objects are deserialized from a JSON representation that was stored during the window's previous shutdown. For your own views and objects to be compatible with refreshing, you'll need to make them play nicely with the serializing and deserializing.
Your package's main module can optionally include a serialize method, which will be called before your package is deactivated. You should return a JSON-serializable object, which will be handed back to you as an object argument to activate next time it is called. In the following example, the package keeps an instance of MyObject in the same state across refreshes.
module.exports = {
activate(state) {
this.myObject = state ? atom.deserializers.deserialize(state) : new MyObject("Hello")
},
serialize() {
return this.myObject.serialize()
}
}
class MyObject {
constructor(data) {
this.data = data
}
serialize() {
return {
deserializer: 'MyObject',
data: this.data
}
}
}
serialize()
Objects that you want to serialize should implement .serialize(). This method should return a serializable object, and it must contain a key named deserializer whose value is the name of a registered deserializer that can convert the rest of the data to an object. It's usually just the name of the class itself.
The other side of the coin is deserializers, whose job is to convert a state object returned from a previous call to serialize back into a genuine object.
deserializers in package.json
The preferred way to register deserializers is via your package's package.json file:
{
"name": "wordcount",
...
"deserializers": {
"MyObject": "deserializeMyObject"
}
}
Here, the key ("MyObject") is the name of the deserializer—the same string used by the deserializer field in the object returned by your serialize() method. The value ("deserializeMyObject") is the name of a function in your main module that'll be passed the serialized data and will return a genuine object. For example, your main module might look like this:
module.exports = {
deserializeMyObject({data}) {
return new MyObject(data)
}
}
Now you can call the global deserialize method with state returned from serialize, and your class's deserialize method will be selected automatically.
An alternative is to use the atom.deserializers.add method with your class in order to make it available to the deserialization system. Usually this is used in conjunction with a class-level deserialize method:
class MyObject {
static initClass() {
atom.deserializers.add(this)
}
static deserialize({data}) {
return new MyObject(data)
}
constructor(data) {
this.data = data;
}
serialize() {
return {
deserializer: 'MyObject',
data: this.data
}
}
}
MyObject.initClass()
While this used to be the standard method of registering a deserializer, the package.json method is now preferred since it allows Atom to defer loading and executing your code until it's actually needed.
class MyObject {
static initClass() {
atom.deserializers.add(this);
this.version = 2;
}
static deserialize(state) {
// ...
}
serialize() {
return {
version: this.constructor.version,
// ...
}
}
}
MyObject.initClass();
Your serializable class can optionally have a class-level @version property and include a version key in its serialized state. When deserializing, Atom will only attempt to call deserialize if the two versions match, and otherwise return undefined. We plan on implementing a migration system in the future, but this at least protects you from improperly deserializing old state.