$$语法：系统组件双向同步
=============

$$运算符为系统组件提供TS变量的引用，使得TS变量和系统组件的内部状态保持同步。

内部状态的具体含义取决于组件。例如，[TextInput](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-textinput)组件的text参数。

#### 使用规则

*   当前$$支持基础类型变量，当该变量使用[@State](https://developer.huawei.com/consumer/cn/doc/harmonyos-guides/arkts-state)、[@Link](https://developer.huawei.com/consumer/cn/doc/harmonyos-guides/arkts-link)、[@Prop](https://developer.huawei.com/consumer/cn/doc/harmonyos-guides/arkts-prop)、[@Provide](https://developer.huawei.com/consumer/cn/doc/harmonyos-guides/arkts-provide-and-consume)等状态管理V1装饰器装饰，或者[@Local](https://developer.huawei.com/consumer/cn/doc/harmonyos-guides/arkts-new-local)等状态管理V2装饰器装饰时，变量值的变化会触发UI刷新。
    
*   当前$$支持的组件：
    
    | 组件 | 支持的参数/属性 | 起始API版本 |
    | :-- | :-- | :-- |
    | [Checkbox](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-checkbox) | select | 10 |
    | [CheckboxGroup](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-checkboxgroup) | selectAll | 10 |
    | [DatePicker](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-datepicker) | selected | 10 |
    | [TimePicker](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-timepicker) | selected | 10 |
    | [MenuItem](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-menuitem) | selected | 10 |
    | [Panel](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-container-panel) | mode | 10 |
    | [Radio](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-radio) | checked | 10 |
    | [Rating](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-rating) | rating | 10 |
    | [Search](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-search) | value | 10 |
    | [SideBarContainer](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-container-sidebarcontainer) | showSideBar | 10 |
    | [Slider](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-slider) | value | 10 |
    | [Stepper](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-stepper) | index | 10 |
    | [Swiper](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-container-swiper) | index | 10 |
    | [Tabs](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-container-tabs) | index | 10 |
    | [TextArea](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-textarea) | text | 10 |
    | [TextInput](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-textinput) | text | 10 |
    | [TextPicker](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-textpicker) | selected、value | 10 |
    | [Toggle](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-toggle) | isOn | 10 |
    | [AlphabetIndexer](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-container-alphabet-indexer) | selected | 10 |
    | [Select](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-select) | selected、value | 10 |
    | [BindSheet](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-universal-attributes-sheet-transition#bindsheet) | isShow | 10 |
    | [BindContentCover](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-universal-attributes-modal-transition#bindcontentcover) | isShow | 10 |
    | [Refresh](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-container-refresh) | refreshing | 8 |
    | [GridItem](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-container-griditem) | selected | 10 |
    | [ListItem](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-container-listitem) | selected | 10 |
    

#### 使用示例

以[TextInput](https://developer.huawei.com/consumer/cn/doc/harmonyos-references/ts-basic-components-textinput)方法的text参数为例：

// xxx.ets
@Entry
@Component
struct TextInputExample {
  @State text: string = '';
  controller: TextInputController = new TextInputController();

  build() {
    Column({ space: 20 }) {
      Text(this.text)
      TextInput({ text: $$this.text, placeholder: 'input your word...', controller: this.controller })
        .placeholderColor(Color.Grey)
        .placeholderFont({ size: 14, weight: 400 })
        .caretColor(Color.Blue)
        .width(300)
    }
    .width('100%')
    .height('100%')
    .justifyContent(FlexAlign.Center)
  }
}

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