Question

我在ObservableCollection CollectionChanged事件中添加新项目时效果非常好，

这是 MVVM代码

public List<BOMForDesignMasterModel> BOMCollection { get; set; } 

public ObservableCollection<BOMForDesignMasterModel> BOM
    {
        get { return _BOM; }
        set
        {
            _BOM = value;
            NotifyPropertyChanged("BOM");
            BOM.CollectionChanged += BOM_CollectionChanged;
        }
    }
public DesignMasterModel DesignMaster
    {
        get
        {
            return _DesignMaster;
        }
        set
        {
            if (value != null)
            {
                _DesignMaster = value;
                BOM.Clear();
                BOM = new ObservableCollection<BOMForDesignMasterModel>(BOMCollection.Where(x => x.DesignMasterId == value.DesignMasterId));
                NotifyPropertyChanged("DesignMaster");
            }
        }
    }
void BOM_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
        if (e.NewItems != null)
            foreach (BOMForDesignMasterModel item in e.NewItems)
                item.PropertyChanged += item_PropertyChanged;
        if (e.OldItems != null)
            foreach (BOMForDesignMasterModel item in e.OldItems)
                item.PropertyChanged -= item_PropertyChanged;

    }
    public String TotalWeight { get { return _TotalWeight; } set { _TotalWeight = value; NotifyPropertyChanged("TotalWeight"); } }
    void item_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        if (e.PropertyName == "Weight")
        {
            TotalWeight = BOM.Sum(x => x.Weight).ToString();
        }
    }

这里使用基于条件的副本集合，

BOM = new ObservableCollection<BOMForDesignMasterModel>(BOMCollection.Where(x => x.DesignMasterId == value.DesignMasterId));

当我确实喜欢这个item_PropertyChanged事件时，无法处理复制的项目。

如何解决此问题？

Answer 1

我认为这是你的问题：

BOM = new ObservableCollection<BOMForDesignMasterModel>(BOMCollection.Where(x => x.DesignMasterId == value.DesignMasterId));

当您新建这样的ObservableCollection时，您不会更改其内容，这将触发NotifyPropertyChanged。您正在更改ObservableCollection的实例，而不是。

虽然您不能只是新建ObservableCollection，但可以使用Clear / Add / Remove来根据需要更改其内容。为了防止你的setter变得太乱，我建议将这个逻辑移到自己的方法中，并找到一些其他方法来触发它。

这看起来像这样：

private void RefreshBOM(int designMasterId)
{
    BOM.Clear();
    var bomResult = BOMCollection.Where(x => x.DesignMasterId == designMasterId);
    if(bomResult != null)
    {
        foreach(var result in bomResult)
        {
            BOM.Add(result);
        }
    }
}

ObservableCollection CollectionChanged事件问题

1 个答案: