singleton.md

## Singleton Pattern

You need to take the singleton and multiton pattern of components into account when invoking the component by API. If the component is singleton, then there will be only one instance when instantiating it multiple times, and there is only one corresponding view layer; If the component is multiton, then a new instance will be created each time you instantiate it, and there are multiple corresponding view layers which don't affect each other.

The components that are involved with api-invoking in cube-ui are all popups. Frequently used ones among them are listed below:

- [Toast](#/en-US/docs/toast)
- [Picker](#/en-US/docs/picker)
- [TimePicker](#/en-US/docs/time-picker)
- [Dialog](#/en-US/docs/dialog)
- [ActionSheet](#/en-US/docs/action-sheet)

All the api-invokings are implemented with the `createAPI` function exported by the [create-api](#/en-US/docs/create-api) module. It is decided whether the component is singleton in definition. See details in [create-api](#/en-US/docs/create-api).

By default, Toast, Dialog and ActionSheet is singleton, while Picker and TimePicker is multiton because their scenes tend to be more complex with a lot of extra data processing. If you want to change the default behavior at the time of instantiation,you can modify the parameter of `$createX`. For example, we change the Dialog into multiton:

```js
const dialog = this.$createDialog({
  type: 'confirm',
  title: 'title',
  content: 'content'
}, false)
dialog.show()
```

In general cases, default behavior can meet the demand, except you have special need.

**Note:** Considering the scenes of Picker and TimePicker, neither of them support singleton pattern.