Observed和ObjectLink数据管理

@Observed
class ClassA {
  public name : string;
  public c: number;
  constructor(c: number, name: string = 'OK') {
    this.name = name;
    this.c = c;
  }
}

class ClassB {
  public a: ClassA;
  constructor(a: ClassA) {
    this.a = a;
  }
}

@Component
struct ViewA {
  label : string = "ep1";
  @ObjectLink a : ClassA;
  build() {
    Column() {
      Text(`ViewA [${this.label}]: a.c=${this.a.c}`)
        .fontSize(20)
      Button(`+1`)
        .width(100)
        .margin(2)
        .onClick(() => {
          this.a.c += 1;
        })
      Button(`reset`)
        .width(100)
        .margin(2)
        .onClick(() => {
          this.a = new ClassA(0); // ERROR, this.a is immutable
        })
    }
  }
}

@Entry
@Component
struct ViewB {
  @State b : ClassB = new ClassB(new ClassA(10));
  build() {
    Flex({direction: FlexDirection.Column, alignItems: ItemAlign.Center}) {
      ViewA({label: "ViewA #1", a: this.b.a})
      ViewA({label: "ViewA #2", a: this.b.a})

      Button(`ViewB: this.b.a.c += 1` )
        .width(320)
        .margin(4)
        .onClick(() => {
          this.b.a.c += 1;
        })
      Button(`ViewB: this.b.a = new ClassA(0)`)
        .width(240)
        .margin(4)
        .onClick(() => {
          this.b.a = new ClassA(0);
        })
      Button(`ViewB: this.b = new ClassB(ClassA(0))`)
        .width(240)
        .margin(4)
        .onClick(() => {
          this.b = new ClassB(new ClassA(0));
        })
    }
  }
}

var nextID: number = 0;
@Observed
class ClassA {
  public name : string;
  public c: number;
  public id : number;
  constructor(c: number, name: string = 'OK') {
    this.name = name;
    this.c = c;
    this.id = nextID++;
  }
}

@Component
struct ViewA {
  label : string = "ViewA1";
  @ObjectLink a: ClassA;
  build() {
    Row() {
      Button(`ViewA [${this.label}] this.a.c= ${this.a.c} +1`)
        .onClick(() => {
          this.a.c += 1;
        })
    }
  }
}

@Entry
@Component
struct ViewB {
  @State arrA : ClassA[] = [ new ClassA(0), new ClassA(0) ];
  build() {
    Column() {
      ForEach (this.arrA, (item) => {
          ViewA({label: `#${item.id}`, a: item})
        },
        (item) => item.id.toString()
      )
      ViewA({label: `ViewA this.arrA[first]`, a: this.arrA[0]})
      ViewA({label: `ViewA this.arrA[last]`, a: this.arrA[this.arrA.length-1]})

      Button(`ViewB: reset array`)
        .onClick(() => {
            this.arrA = [ new ClassA(0), new ClassA(0) ];
        })
      Button(`ViewB: push`)
        .onClick(() => {
            this.arrA.push(new ClassA(0))
        })
      Button(`ViewB: shift`)
        .onClick(() => {
            this.arrA.shift()
        })
    }
  }
}