List局部刷新，有人知道怎么处理吗？

@Component 
struct Child { 
  @Link items: TestList[]; 
 
  build() { 
    Column() { 
      ForEach(this.items, (item: TestList) => { 
        ChildChild({ item: item }); 
      }) 
      Button(`Button: push`).onClick(() => { 
        this.items[0].index1 = 3; 
        this.items[0].str = 'Third'; 
      }) 
    } 
  } 
} 
 
@Component 
struct ChildChild { 
  @State item: TestList = new TestList(); 
 
  build() { 
    Column() { 
      Text(`${this.item.index1}+'-----'${this.item.str}`) 
    } 
  } 
} 
 
@Entry 
@Component 
struct Parent { 
  @State arr: TestList[] = []; 
  aboutToAppear() { 
    let test1: TestList = new TestList(); 
    test1.index1 = 1; 
    test1.str = 'First'; 
    this.arr.push(test1) 
    let test2: TestList = new TestList(); 
    test2.index1 = 2; 
    test2.str = 'Second'; 
    this.arr.push(test2) 
  } 
 
  build() { 
    Column() { 
      Child({ items: this.arr }) 
      Button(`Button: push`).onClick(() => { 
        this.arr[1].index1 = 4; 
        this.arr[1].str = 'Fourth'; 
      }) 
    } 
  } 
} 
 
@Observed 
class TestList { 
  index1: number = 0; 
  str: string = ''; 
}