# ArkUI Subsystem Changelog

## cl.arkui.1 Support for the undefined Parameter by Universal Events

Added support for passing **undefined** as a parameter for universal events (click, touch, show/hide, key, focus, mouse, and component area change events).

**Example**

```ts
// xxx.ets
@Entry
@Component
struct Example {
  build() {
    Button("test")
    .onClick(()=>{
      console.log("click");
    })
    .onClick(undefined)
  }
}
```

**Change Impact**

If the event callback parameter is **undefined**, the system will not respond to the configured event callback.


**Key API/Component Changes**

N/A

**Adaptation Guide**

If the event parameter is set to **undefined**, the event is disabled. Set the parameter based on the use case.


## cl.arkui.2 Initialization Requirement Change of @Prop/@BuilderParam Decorated Variables

**Example**

```ts
// xxx.ets
@Entry
@Component
struct Parent {
  @State message: string = 'Parent'
  build() {
    Column() {
      Child() // Compile time error.
    }
  }
}

@Component
struct Child {
  @Prop message: string
  build() {
    Column() {
      
    }
  }
}
```

**Change Impact**

If the @Prop or @BuilderParam decorated variable is not initialized locally or initialized from its parent component, a compile time error will occur.


**Key API/Component Changes**

N/A

**Adaptation Guide**

Assign an initial value to the @Prop or @BuilderParam decorated variable or pass the value from the parent component.


## cl.arkui.3 Initial Value Requirement Change of @BuilderParam Decorated Variables

**Example**

```ts
// xxx.ets
@Builder
function builderFunction() {
  Text('Hello Builder')
}

function normal () {

}

@Component
struct Index {
  @BuilderParam builderParam: ()=>void = builderFunction
  @BuilderParam builderParam2: ()=>void = normal // Compile time error.
  build() {
    Column() {

    }
  }
}
```

**Change Impact**

If the initial value of the @BuilderParam decorated variable is not an @Builder method, the compilation will fail.


**Key API/Component Changes**

N/A

**Adaptation Guide**

Pass in an @Builder method as the initial value of the @BuilderParam variable.

## cl.arkui.4 Type Change of the searchButton Attribute in the \<Search> Component from SearchButtonOption to SearchButtonOptions

**Change Impact**

If the **SearchButtonOption** type is explicitly used, the compilation will fail.

**Key API/Component Changes**

The type of the **searchButton** attribute is changed from **SearchButtonOption** to **SearchButtonOptions**.

**Adaptation Guide**

Change **SearchButtonOption** to **SearchButtonOptions**.

## cl.arkui.5 Type Change of the BindSheet Attribute in Overlay Components from SheetStyle to SheetOptions

**Change Impact**

If the **SheetStyle** type is explicitly used, the compilation will fail.

**Key API/Component Changes**

The type of the **BindSheet** attribute is changed from **SheetStyle** to **SheetOptions**.

**Adaptation Guide**

Change **SheetStyle** to **SheetOptions**.

## cl.arkui.6 Change of the Value Returned by onBackPress from void to void | boolean for Custom Components

**Example**

```ts
// xxx.ets
@Entry
@Component
struct Index {
  async onBackPress() {}    // Compile-time error
  build() {
    Column() {

    }
  }
}
```

**Change Impact**

When the lifecycle function **onBackPress** of a custom component is modified with **async**, the compilation fails.

**Key API/Component Changes**

**onBackPress? (): void** is changed to **onBackPress? (): void | boolean**.

**Adaptation Guide**

The custom component lifecycle APIs are synchronous callbacks invoked by the system when appropriate. They must be used according to the synchronous API specifications defined by the SDK. Do not use modifiers such as **async** to change API specifications.