OpenHarmony组件内状态变量使用：@State装饰器

// for simple type
@State count: number = 0;
// value changing can be observed
this.count = 1;

  class ClassA {
    public value: string;

    constructor(value: string) {
      this.value = value;
    }
  }

  class Model {
    public value: string;
    public name: ClassA;
    constructor(value: string, a: ClassA) {
      this.value = value;
      this.name = a;
    }
  }

// class类型
 @State title: Model = new Model('Hello', new ClassA('World'));

// class类型赋值
this.title = new Model('Hi', new ClassA('ArkUI'));

// class属性的赋值
this.title.value = 'Hi'

// 嵌套的属性赋值观察不到
this.title.name.value = 'ArkUI'

class Model {
  public value: number;
  constructor(value: number) {
    this.value = value;
  }
}

@State title: Model[] = [new Model(11), new Model(1)]

this.title = [new Model(2)]

this.title[0] = new Model(2)

this.title.pop()

this.title.push(new Model(12))

@Entry
@Component
struct DatePickerExample {
  @State selectedDate: Date = new Date('2021-08-08')

  build() {
    Column() {
      Button('set selectedDate to 2023-07-08')
        .margin(10)
        .onClick(() => {
          this.selectedDate = new Date('2023-07-08')
        })
      Button('increase the year by 1')
        .margin(10)
        .onClick(() => {
          this.selectedDate.setFullYear(this.selectedDate.getFullYear() + 1)
        })
      Button('increase the month by 1')
        .margin(10)
        .onClick(() => {
          this.selectedDate.setMonth(this.selectedDate.getMonth() + 1)
        })
      Button('increase the day by 1')
        .margin(10)
        .onClick(() => {
          this.selectedDate.setDate(this.selectedDate.getDate() + 1)
        })
      DatePicker({
        start: new Date('1970-1-1'),
        end: new Date('2100-1-1'),
        selected: this.selectedDate
      })
    }.width('100%')
  }
}

@Entry
@Component
struct MyComponent {
  @State count: number = 0;

  build() {
    Button(`click times: ${this.count}`)
      .onClick(() => {
        this.count += 1;
      })
  }
}

class Model {
  public value: string;

  constructor(value: string) {
    this.value = value;
  }
}

@Entry
@Component
struct EntryComponent {
  build() {
    Column() {
      // 此处指定的参数都将在初始渲染时覆盖本地定义的默认值，并不是所有的参数都需要从父组件初始化
      MyComponent({ count: 1, increaseBy: 2 })
      MyComponent({ title: new Model('Hello, World 2'), count: 7 })
    }
  }
}

@Component
struct MyComponent {
  @State title: Model = new Model('Hello World');
  @State count: number = 0;
  private increaseBy: number = 1;

  build() {
    Column() {
      Text(`${this.title.value}`)
      Button(`Click to change title`).onClick(() => {
        // @State变量的更新将触发上面的Text组件内容更新
        this.title.value = this.title.value === 'Hello ArkUI' ? 'Hello World' : 'Hello ArkUI';
      })

      Button(`Click to increase count=${this.count}`).onClick(() => {
        // @State变量的更新将触发该Button组件的内容更新
        this.count += this.increaseBy;
      })
    }
  }
}

@State title: Model = new Model('Hello World');
@State count: number = 0;

class C1 {
   public count:number;
   public increaseBy:number;
   constructor(count: number, increaseBy:number) {
   this.count = count;
   this.increaseBy = increaseBy;
  }
}
let obj = new C1(1, 2)
MyComponent(obj)