DataGrid 未绑定到 ObservableCollection答案

【问题标题】：DataGrid is not bound to the ObservableCollectionDataGrid 未绑定到 ObservableCollection
【发布时间】：2017-08-16 07:48:53
【问题描述】：

我的视图中有一个按钮，可以在 ViewModel 中执行此方法：

public void GetAudits(Guid? userId, DateTime? from, DateTime? to, string form)
        {
            StringBuilder sCondition = new StringBuilder("WHERE 0=0");

            if (userId != null && userId != Guid.Empty)
                sCondition.Append(string.Format(" AND UserId = '{0}' ", userId));

            if (!string.IsNullOrEmpty(form))
                sCondition.Append(string.Format(" AND FormName = '{0}' ", form));


            string query = string.Format("SELECT * FROM Common.TbHistoryLog {0}", sCondition);
            Audits = new ObservableCollection<HistoryLog>(oContext.Database.SqlQuery<HistoryLog>(query).ToList());

        }

Audits 属性：

 public ObservableCollection<HistoryLog> Audits
    {
        get
        {
            return audits;
        }
        set
        {
            audits = value;
        }
    }
    ObservableCollection<HistoryLog> audits;

这是按钮的处理程序：

private void BtnSearch(object sender, RoutedEventArgs e)
        {
            var userId = ((TbUsers)cmbUsers.SelectedItem)?.UserId;
            var from = dtFromDate.Value;
            var to = dtToDate.Value;
            var form = ((BlCommon.TbObjects)cmbForms.SelectedItem)?.ObjectRealName;
            using (ClsUserTransactions oUserTrans = new ClsUserTransactions())
            {
                oUserTrans.GetAudits(userId, from, to, form);
            }
        }

但是当我单击按钮时，dataGrid 不会使用 Audits 集合进行更新：

<DataGrid  Name="gvHistory" Grid.Column="0" Grid.Row="9" Margin="2" Visibility="Visible" ItemsSource="{Binding Audits}" Grid.ColumnSpan="8" IsReadOnly="True" Grid.RowSpan="2"  AutoGenerateColumns="True" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" CanUserAddRows="False"/>

当我调试时，我注意到 getter 块没有被命中

【问题讨论】：

在 ViewModel 中实现 INotifyPropertyChanged 并在 setter 中为“Audits”属性引发 PropertyChanged 事件
Observable 集合属性应该是只读的。它们向 UI 提供更改通知。在集合中添加和删除元素，不要替换集合。

标签： c# wpf mvvm datagrid observablecollection

【解决方案1】：

您为什么不简单地清除并重新填充相同的ObservableCollection？：

public void GetAudits(Guid? userId, DateTime? from, DateTime? to, string form)
{
    StringBuilder sCondition = new StringBuilder("WHERE 0=0");

    if (userId != null && userId != Guid.Empty)
        sCondition.Append(string.Format(" AND UserId = '{0}' ", userId));

    if (!string.IsNullOrEmpty(form))
        sCondition.Append(string.Format(" AND FormName = '{0}' ", form));


    string query = string.Format("SELECT * FROM Common.TbHistoryLog {0}", sCondition);
    if (Audits != null)
    {
        Audits.Clear();
        var newItems = oContext.Database.SqlQuery<HistoryLog>(query).ToList();
        if (newItems != null)
            foreach (var newItem in newItems)
                Audits.Add(newItem);
    }
}

其次，这会创建一个ClsUserTransactions 的新实例：

ClsUserTransactions oUserTrans = new ClsUserTransactions())

您需要将项目添加到DataGrid 绑定的项目，并且您当然不应该在填充其审核集合后立即处置该实例...：

private void BtnSearch(object sender, RoutedEventArgs e)
{
    var userId = ((TbUsers)cmbUsers.SelectedItem)?.UserId;
    var from = dtFromDate.Value;
    var to = dtToDate.Value;
    var form = ((BlCommon.TbObjects)cmbForms.SelectedItem)?.ObjectRealName;
    ClsUserTransactions oUserTrans = gvHistory.DataContext as ClsUserTransactions;
    oUserTrans.GetAudits(userId, from, to, form);
}

【讨论】：

【解决方案2】：

您的 ViewModel 应该实现 INotifyPropertyChanged 接口，然后在 Audits setter 上通知属性更改：

public class ViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged(string name)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(name));
        }
    }
...

public ObservableCollection<HistoryLog> Audits
{
    get
    {
        return audits;
    }
    set
    {
        audits = value;
        OnPropertyChanged("Audits");
    }
}
ObservableCollection<HistoryLog> audits;

【讨论】：