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当模型属性设置为新实例时更新MVVM视图

mvvm wpf c#

Rob King · 技术社区 · 13 年前

我在WPF应用程序中有一个ViewModel和一个View。在屏幕上可以选择输入(日期选择器、文本框和组合框)。

输入绑定到ViewModel的NewItem属性,DataGrid绑定到WorkLog集合属性。

当用户单击“添加”按钮时,我希望将NewItem添加到WorkLog集合中,并重置NewItem属性以允许用户添加更多项目。问题是,当我添加项目时,如果我重新实例化NewItem,那么控件仍然被填充,但在后台,VM值都是默认值(或null),所以它不起作用。

如何重置NewItem属性并更新UI以反映这一点?我尝试了INotifyPropertyChanged,但没有成功(因为我正在设置新实例,而不是更改值)。

为了简洁起见,我对代码进行了删减

模型

public class WorkLogItem : INotifyPropertyChanged
{
    public WorkLogItem()
    {
        this.Datestamp = DateTime.Today;
        this.Staff = new Lookup();
        this.WorkItem = new Lookup();
    }

    #region ID

    private Int32 _ID;

    public Int32 ID
    {
        get { return this._ID; }
        set
        {
            this._ID = value;
            FirePropertyChanged("ID");
        }
    }

    #endregion

    #region Datestamp

    private DateTime? _Datestamp;

    public DateTime? Datestamp
    {
        get { return this._Datestamp; }
        set
        {
            this._Datestamp = value;
            FirePropertyChanged("Datestamp");
        }
    }

    #endregion

    #region Staff

    private Model.Lookup _Staff;

    public Model.Lookup Staff
    {
        get { return this._Staff; }
        set
        {
            this._Staff = value;
            FirePropertyChanged("Staff");
        }
    }

    #endregion

    #region WorkItem

    private Model.Lookup _WorkItem;

    public Model.Lookup WorkItem
    {
        get { return this._WorkItem; }
        set
        {
            this._WorkItem = value;
            FirePropertyChanged("WorkItem");
        }
    }

    #endregion

    #region Hours

    private Decimal _Hours;

    public Decimal Hours
    {
        get { return this._Hours; }
        set
        {
            this._Hours = value;
            FirePropertyChanged("Hours");
        }
    }

    #endregion

    public event PropertyChangedEventHandler PropertyChanged;

    // Create the OnPropertyChanged method to raise the event
    protected void FirePropertyChanged(String name)
    {
        PropertyChangedEventHandler handler = PropertyChanged;

        if (handler != null)
            handler(this, new PropertyChangedEventArgs(name));
    }
}

查看模型

public Model.WorkLogItem NewItem { get; set; }

public ObservableCollection<Model.WorkLogItem> WorkLog { get; set; }

看法

<Label Content="Date " />
<DatePicker SelectedDate="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}, Path=DataContext.NewItem.Datestamp, NotifyOnSourceUpdated=True}" />

<Label Content="Work Item " />
<ComboBox Grid.Column="1" Grid.Row="2" DataContext="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}, Path=DataContext.WorkItems}" ItemsSource="{Binding}" DisplayMemberPath="Value" SelectedValuePath="ID" SelectedItem="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}, Path=DataContext.WorkLogItem.Type, NotifyOnSourceUpdated=True}" IsSynchronizedWithCurrentItem="True" />

<Label Grid.Row="3" Content="Hours " />
<TextBox Grid.Column="1" Grid.Row="3" Text="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Window}}, Path=DataContext.NewItem.Hours, NotifyOnSourceUpdated=True}" />

在加载的窗口中(_L):

this.DataContext = this.VM;

在Add_Click中

this.VM.WorkLog.Add(this.VM.NewItem);

this.VM.NewItem = new Model.WorkLogItem();

2 回复 | 直到 13 年前

Ed Chapel 13 年前

你的 ViewModel 还必须执行 INotifyPropertyChanged

public class ViewModel : INotifyPropertyChanged
{
    private Model.WorkLogItem _newItem;

    public ViewModel()
    {
        NewItem = new Model.WorkLogItem();
        WorkLog  = new ObservableCollection<Model.WorkLogItem>();
    }

    public Model.WorkLogItem NewItem
    { 
        get { return _newItem; }
        set
        {
            _newItem = value;
            FirePropertyChanged("NewItem");
        }
    }

    public ObservableCollection<Model.WorkLogItem> WorkLog { get; set; }

    // INotifyPropertyChanged implementation here...
}

当绑定到您的 ComboBox ,请务必使用 Mode=TwoWay :

<ComboBox ... SelectedItem="{Binding ... Mode=TwoWay}" />

Sheridan 13 年前

我这样做的方法是在数据对象中设置一个空构造函数,将其所有财产设置为默认值。然后,当我想将视图“重置”为所有空字段时,我只需将数据绑定属性设置为一个新项:

NewItem = new YourDataType();

这将按预期更新所有数据绑定控件的财产。请注意,我的数据类型类都实现了 INotifyPropertyChanged 接口,并且这种清除UI控件的方法只有在它们确实实现了它的情况下才会起作用。