1# $$ Syntax: Two-Way Synchronization of Built-in Components 2 3 4The $$ operator provides a TypeScript variable by-reference to a built-in component so that the variable value and the internal state of that component are kept in sync. 5 6 7What the internal state is depends on the component. For example, for the [\<TextInput>](../reference/apis-arkui/arkui-ts/ts-basic-components-textinput.md) component, it is the **text** parameter. 8 9 10> **NOTE** 11> 12> $$ is also used for [by-reference parameter passing for the @Builder decorator](arkts-builder.md#by-reference-parameter-passing). Pay attention to the differences between the two usages. 13 14 15## Rules of Use 16 17- $$ supports variables of simple types and variables decorated by \@State, \@Link, or \@Prop. 18 19- $$ supports the components listed below. 20 21 | Component | Supported Parameter/Attribute| Initial API Version| 22 | ------------------------------------------------------------ | --------------- | ----------- | 23 | [Checkbox](../reference/apis-arkui/arkui-ts/ts-basic-components-checkbox.md) | select | 10 | 24 | [CheckboxGroup](../reference/apis-arkui/arkui-ts/ts-basic-components-checkboxgroup.md) | selectAll | 10 | 25 | [DatePicker](../reference/apis-arkui/arkui-ts/ts-basic-components-datepicker.md) | selected | 10 | 26 | [TimePicker](../reference/apis-arkui/arkui-ts/ts-basic-components-timepicker.md) | selected | 10 | 27 | [MenuItem](../reference/apis-arkui/arkui-ts/ts-basic-components-menuitem.md) | selected | 10 | 28 | [Panel](../reference/apis-arkui/arkui-ts/ts-container-panel.md) | mode | 10 | 29 | [Radio](../reference/apis-arkui/arkui-ts/ts-basic-components-radio.md) | checked | 10 | 30 | [Rating](../reference/apis-arkui/arkui-ts/ts-basic-components-rating.md) | rating | 10 | 31 | [Search](../reference/apis-arkui/arkui-ts/ts-basic-components-search.md) | value | 10 | 32 | [SideBarContainer](../reference/apis-arkui/arkui-ts/ts-container-sidebarcontainer.md) | showSideBar | 10 | 33 | [Slider](../reference/apis-arkui/arkui-ts/ts-basic-components-slider.md) | value | 10 | 34 | [Stepper](../reference/apis-arkui/arkui-ts/ts-basic-components-stepper.md) | index | 10 | 35 | [Swiper](../reference/apis-arkui/arkui-ts/ts-container-swiper.md) | index | 10 | 36 | [Tabs](../reference/apis-arkui/arkui-ts/ts-container-tabs.md) | index | 10 | 37 | [TextArea](../reference/apis-arkui/arkui-ts/ts-basic-components-textarea.md) | text | 10 | 38 | [TextInput](../reference/apis-arkui/arkui-ts/ts-basic-components-textinput.md) | text | 10 | 39 | [TextPicker](../reference/apis-arkui/arkui-ts/ts-basic-components-textpicker.md) | selected, value| 10 | 40 | [Toggle](../reference/apis-arkui/arkui-ts/ts-basic-components-toggle.md) | isOn | 10 | 41 | [AlphabetIndexer](../reference/apis-arkui/arkui-ts/ts-container-alphabet-indexer.md) | selected | 10 | 42 | [Select](../reference/apis-arkui/arkui-ts/ts-basic-components-select.md) | selected, value| 10 | 43 | [BindSheet](../reference/apis-arkui/arkui-ts/ts-universal-attributes-sheet-transition.md) | isShow | 10 | 44 | [BindContentCover](../reference/apis-arkui/arkui-ts/ts-universal-attributes-modal-transition.md) | isShow | 10 | 45 | [Refresh](../reference/apis-arkui/arkui-ts/ts-container-refresh.md) | refreshing | 8 | 46 47- When the variable bound to $$ changes, the UI is re-rendered synchronously. 48 49 50## Example 51 52This example uses the **text** parameter of the [\<TextInput>](../reference/apis-arkui/arkui-ts/ts-basic-components-textinput.md) component. 53 54 55```ts 56// xxx.ets 57@Entry 58@Component 59struct TextInputExample { 60 @State text: string = '' 61 controller: TextInputController = new TextInputController() 62 63 build() { 64 Column({ space: 20 }) { 65 Text(this.text) 66 TextInput({ text: $$this.text, placeholder: 'input your word...', controller: this.controller }) 67 .placeholderColor(Color.Grey) 68 .placeholderFont({ size: 14, weight: 400 }) 69 .caretColor(Color.Blue) 70 .width(300) 71 }.width('100%').height('100%').justifyContent(FlexAlign.Center) 72 } 73} 74``` 75 76 77 78
