@Require Decorator: Validating Constructor Input Parameters

@Require is a decorator for declaring that parameters must be passed in to the constructor. This decorator must be used with @Prop or @BuilderParam.

NOTE

This decorator is supported since API version 11.

Overview

When @Require is used together with @Prop or @BuilderParam, parameters must be passed in to the constructor of a custom component.

Constraints

The @Require decorator can only decorate an @Prop or @BuilderParam decorated member variable in a struct.

Use Scenarios

When the @Require decorator is used together with @Prop or @BuilderParam in the Child component, the parent component Index must pass in parameters for constructing the Child component. Otherwise, the compilation fails.

@Entry
@Component
struct Index {
  @State message: string = 'Hello World';

  @Builder buildTest() {
    Row() {
      Text('Hello, world')
        .fontSize(30)
    }
  }

  build() {
    Row() {
      Child({ initMessage: this.message, message: this.message,
        buildTest: this.buildTest, initBuildTest: this.buildTest })
    }
  }
}

@Component
struct Child {
  @Builder buildFuction() {
    Column() {
      Text('initBuilderParam')
        .fontSize(30)
    }
  }

  @Require @BuilderParam buildTest: () => void;
  @Require @BuilderParam initBuildTest: () => void = this.buildFuction;
  @Require @Prop initMessage: string = 'Hello';
  @Require @Prop message: string;

  build() {
    Column() {
      Text(this.initMessage)
        .fontSize(30)
      Text(this.message)
        .fontSize(30)
      this.initBuildTest();
      this.buildTest();
    }
    .width('100%')
    .height('100%')
  }
}

Incorrect Usage

@Entry
@Component
struct Index {
  @State message: string = 'Hello World';

  @Builder buildTest() {
    Row() {
      Text('Hello, world')
        .fontSize(30)
    }
  }

  build() {
    Row() {
      Child()
    }
  }
}

@Component
struct Child {
  @Builder buildFuction() {
    Column() {
      Text('initBuilderParam')
        .fontSize(30)
    }
  }
  // As @Require is used here, parameters must be passed in to the constructor.
  @Require @BuilderParam initBuildTest: () => void = this.buildFuction;
  @Require @Prop initMessage: string = 'Hello';

  build() {
    Column() {
      Text(this.initMessage)
        .fontSize(30)
      this.initBuildTest();
    }
  }
}