MVVM:命令和canExecute标志

Question

我正在使用带有动态标志canExecute的第一个命令。

我有保存命令，只有当用户更改某些数据时，它才能启用。

我想在制作mod时绑定一个操作，但我遇到了错误，也许这不是正确的方式。

这是我的xaml（正如你所看到的，我所有的字段都在一个布局控件中）：

            <dxlc:LayoutGroup Header="Configurazione tecnica" View="GroupBox" Orientation="Vertical">
                <dxlc:LayoutItem Label="Tipo sistema">
                    <dxe:ComboBoxEdit IsTextEditable="False" EditValue="{Binding IDTTS}" ItemsSource="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}},Path=DataContext.tts}"  />
                </dxlc:LayoutItem>
                <dxlc:LayoutItem Label="Locazione">
                    <!--<dxe:ComboBoxEdit  EditValue="{Binding REMOTO}" ItemsSource="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}},Path=DataContext.locations}"  />-->
                    <StackPanel Margin="0" Orientation="Horizontal" VerticalAlignment="Center" HorizontalAlignment="Left">
                        <RadioButton x:Name="rd_LOCALE" Content="{DynamicResource Locale}" Margin="10,0,0,0" VerticalAlignment="Center" GroupName="Location" IsChecked="True" Panel.ZIndex="9" TabIndex="10" />
                        <RadioButton Content="{DynamicResource Remoto}" Margin="10,0,6,0" x:Name="rd_REMOTO" Tag="PRISMA" VerticalAlignment="Center" IsChecked="{Binding REMOTO}" GroupName="Location" Panel.ZIndex="10" TabIndex="11" />
                    </StackPanel>
                </dxlc:LayoutItem>
                <dxlc:LayoutItem Label="Tipo di connessione">
                    <!--<dxe:ComboBoxEdit  EditValue="{Binding TIPOCONN}" />-->
                    <StackPanel Margin="0" Orientation="Horizontal" VerticalAlignment="Center">
                        <RadioButton Content="{DynamicResource Terminale}" Margin="10,0,0,0" x:Name="rd_TIPOCONN" Tag="PRISMA" VerticalAlignment="Center" GroupName="TipoConn" IsChecked="True" Panel.ZIndex="11" TabIndex="12" />
                        <RadioButton x:Name="rd_SLAVE" Content="Slave" Margin="10,0,6,0" Tag="PRISMA" VerticalAlignment="Center" IsChecked="{Binding TIPOCONN}" GroupName="TipoConn" Panel.ZIndex="12" TabIndex="13" />
                    </StackPanel>
                </dxlc:LayoutItem>
            </dxlc:LayoutGroup>
            <dxlc:LayoutGroup Header="Centralina STK" View="GroupBox" Orientation="Vertical">
                <dxlc:LayoutItem >
                    <!--<dxe:ComboBoxEdit  EditValue="{Binding SERMATIC}" />-->
                    <StackPanel DockPanel.Dock="Top" Orientation="Horizontal" HorizontalAlignment="Center" Margin="0,6">
                        <RadioButton x:Name="rd_sermatic" Content="{DynamicResource SI}" Margin="10,0,0,0"  Tag="PRISMA" VerticalAlignment="Center" Width="100" HorizontalAlignment="Left" IsChecked="{Binding SERMATIC}" GroupName="stk" Panel.ZIndex="13" TabIndex="14" />
                        <RadioButton x:Name="rd_sermaticNO" Content="{DynamicResource NO}" Margin="10,0,0,0" Tag="PRISMA" VerticalAlignment="Center" Width="100" HorizontalAlignment="Left" GroupName="stk" IsChecked="True" Panel.ZIndex="14" TabIndex="15" />
                    </StackPanel>
                </dxlc:LayoutItem>
                <dxlc:LayoutItem >
                    <!--<dxe:ComboBoxEdit  EditValue="{Binding SERMATICCOM}"/>-->
                    <UniformGrid Rows="1" Columns="2" DockPanel.Dock="Top" Margin="4,0,4,4" IsEnabled="{Binding IsChecked, ElementName=rd_sermatic}">
                        <TextBlock Margin="0" TextWrapping="Wrap" Text="{DynamicResource PortaCOM}" TextAlignment="Right" VerticalAlignment="Center" HorizontalAlignment="Right"/>
                        <ComboBox x:Name="cmb_SERMATICCOM" Height="23" Margin="10,2,0,0" Panel.ZIndex="15" TabIndex="16">
                            <ComboBoxItem Content="----" />
                            <ComboBoxItem Content="COM1" />
                            <ComboBoxItem Content="COM2" />
                            <ComboBoxItem Content="COM3" />
                            <ComboBoxItem Content="COM4" />
                            <ComboBoxItem Content="COM5" />
                            <ComboBoxItem Content="COM6" />
                            <ComboBoxItem Content="COM7" />
                            <ComboBoxItem Content="COM8" />
                        </ComboBox>
                    </UniformGrid>
                </dxlc:LayoutItem>
            </dxlc:LayoutGroup>
        </dxlc:LayoutControl>

这是我的MainWindowVIewModel，我在其中定义命令和canExceute:

private bool CanSave()
{
    return SaveButtonEnabled;
}
public ICommand SaveCommand { get; private set; }
void EnableSave(NotifyCollectionChangedEventArgs e)
{
    if (e.Action == NotifyCollectionChangedAction.Replace)
        SaveButtonEnabled = true;
}
private bool p_saveButtonEnabled=false;
public bool SaveButtonEnabled
{
    get{ return p_saveButtonEnabled; }
    set
        {
        p_saveButtonEnabled = value;
        base.RaisePropertyChangedEvent("SaveButtonEnabled");
    }
}
private void SaveData()
{
    MainWindow.dbContext.SaveChanges();
    SaveButtonEnabled = false;
    //base.RaisePropertyChangedEvent("SaveButtonEnabled");
}

当我填充observableColletion时，在绑定的用户控件中更改数据，我得到了：

ListaImpianti.CollectionChanged += (s, e) => EnableSave(e);

ListaImpanti以这种方式绑定到xaml：

<DockPanel Grid.Row="1" Margin="0,60,0,0">
    <dxg:GridControl x:Name="lst1" ItemsSource="{Binding ListaImpianti}"  EnableSmartColumnsGeneration="True" FilterCriteria="{Binding FilterCriteria, ElementName=searchControl}"  MaxHeight="500" Height="266" VerticalAlignment="Top" Margin="0,-27,0,0" Width="332" ShowBorder="False">
        <dxg:GridControl.Columns>
            <dxg:GridColumn x:Name="CODICE" Binding="{Binding CODICE}" FieldName="CODICE"/>
            <dxg:GridColumn x:Name="NOME" Binding="{Binding NOME}" FieldName="NOME"/>
        </dxg:GridControl.Columns>
        <dxg:GridControl.View>
            <dxg:TableView AllowPerPixelScrolling="True" AllowEditing="False" ShowGroupPanel="False" ShowFilterPanelMode="Never"  />
        </dxg:GridControl.View>
     </dxg:GridControl>
</DockPanel>

ListaImpanti定义为：

 public ObservableCollection<TabImpianti> ListaImpianti
 {
    get { return p_ListaImpianti; }
    set
    {
        p_ListaImpianti = value;
        base.RaisePropertyChangedEvent("ListaImpianti");
    }
}
[...]
p_ListaImpianti = new ObservableCollection<TabImpianti>();
var query2 = (from r in MainWindow.dbContext.TabImpianti select r);
foreach (TabImpianti ti in query2) { p_ListaImpianti.Add(ti); }

但从未调用enable-save。。为什么？

Piero

Answer 1

如果用户更改了什么，视图模型就会知道，对吧？对我来说，标志SaveButtonEnabled应该由视图模型本身更改，而不是由绑定到视图的任何命令更改。

例如，如果用户更改SERMATIC属性，则该属性的setter是您必须在必要时更改标志的位置。

附带说明：将这些base.RaisePropertyChangedEvent("SaveButtonEnabled")片段移动到SaveButtonEnabled属性的setter中。

Answer 2

通常，如果您想在属性更改时完成某些操作，您会为PropertyChangedEvent添加一个侦听器。当有许多属性时，这不会改变，这里有一个可能的实现：为包含要监视的属性的viewModel的PropertyChanged事件注册一个侦听器，并检查更改后的属性的名称是否与您想要监视的属性之一匹配。如果是，请启用保存按钮。

MainWindowViewModel()
{
  otherVewModel.PropertyChanged += ( s, e ) => EnableSaveIfCertainPropertiesChange( e );
}
List<string> propertiesTriggeringEnableSave = new List<string> {
  "IDTTS", "REMOTO", "TIPOCONN" //and so on
};
void EnableSaveIfCertainPropertiesChange( PropertyChangedEventArgs e )
{
  if( propertiesTriggeringEnableSave.Contains( e.PropertyName ) )
    SaveButtonEnabled = true;
}
public bool SaveButtonEnabled
{
  get{ return saveButtonEnabled; }
  set
  {
    saveButtonEnabled = value;
    base.RaisePropertyChangedEvent("SaveButtonEnabled");
  }
}
bool saveButtonEnabled

还有一些通用指南：注意，我将SaveButtonEnabled更改为mvvm中常用的方式：这比您现在使用的更好，因为您不必重复RaisePropertyChangedEvent行（容易出错）。此外，我不会为命令的延迟初始化而烦恼，边际（如果有的话）性能增益会产生更丑陋的代码。在我看来，如果你的命令在像这样的构造函数中初始化，代码会更短、更可读

MainViewModel()
{
  SaveCommand = new DelegateCommand( Save, CanSave );
}
public ICommand SaveCommand{ get; private set; }