FormArray 調整數據位置

get beans() {
    return this.validateForm.get('beans') as FormArray;
}

change(fromIdx, toIdx){
    const formGroup = this.beans.at(fromIdx);
    this.beans.removeAt(fromIdx);
    this.beans.insert(toIdx, formGroup);
}

trackByFn(index: any, item: any) {
    return index;
}

同時需要在ng-for循環部分增加trackBy
*ngFor="let item of beans.controls; let i = index; trackBy:trackByFn"