Binding to DataGridColumn with IMultiValueConverter encounters issues while using a similiar IValueConverter does not

问题

I have 2 Datagrid checkbox columns each with a binding.

    <DataGrid ItemsSource="{Binding}" Name="DataGrid1" DataContext="{Binding Source={StaticResource TableViewSource}}">
        <DataGridCheckBoxColumn Header="Required" Width="50" MinWidth="50">
            <DataGridCheckBoxColumn.Binding>
                <Binding Path="Required" Converter="{StaticResource DateTimeToBooleanConverter}"/>
            </DataGridCheckBoxColumn.Binding>
        </DataGridCheckBoxColumn>
        <DataGridCheckBoxColumn Header="Required Test" Width="60" MinWidth="60">
            <DataGridCheckBoxColumn.Binding>
                <MultiBinding Converter="{StaticResource DateTimeToBooleanMultiverter}">
                    <Binding Path="Required_Date" />
                    <Binding Path="Required_Time" />
                </MultiBinding>
            </DataGridCheckBoxColumn.Binding>
        </DataGridCheckBoxColumn>
    </DataGrid>

The bindings simply write the date/time the box was checked to the db field "Required" and null when unchecked.

In the first checkbox everything works great with the following converter:

public class DateTimeToBooleanConverter : IValueConverter
{

public object Convert(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
    if (value != null) {
        return true;
    } else {
        return false;
    }
}

public object ConvertBack(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
    if (value == true) {
        return System.DateTime.Now.Date;
    } else {
        return null;
    }
}
}

In the last column I wanted to save the date and time into 2 different fields "Required_Date" and "Required_Time" (String). The following IMultiConverter was created to handle it:

public class DateTimeToBooleanMultiverter : IMultiValueConverter
{

public object Convert(object[] values, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
    if (values[0] != null) {
        return true;
    } else {
        return false;
    }
}

public object[] ConvertBack(object value, System.Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
{
    if (value != null) {
        if (value == true) {
            return {
                System.DateTime.Now.Date,
                System.DateTime.Now.TimeOfDay.ToString()
            };
        }
    }
    return {
        null,
        null
    };
}
}

On initial load the column looks good. The column has all the appropriate cell checked. However, when the value is checked/unchecked I get the following binding error.

System.Windows.Data Error: 5 : Value produced by BindingExpression is not valid for target property.; Value='True' MultiBindingExpression:target element is 'DataGridCell' (Name=''); target property is 'CellContent' (type 'String')

Further, when I uncheck a cell it doesn't uncheck properly and I notice through some breakpoints in my converter that values are coming in as DependencyProperty.Unset (Probably due to the binding warning).

(9-30-12)

I found a more promising lead in a codeplex comment:

"The reason that MultiBindings are not working is that DataGridHelper.UpdateSource uses GetBindingExpression and not GetBindingExpressionBase. If this is changed multi and priority bindings should work."

I attempted to set updating to Explicit and create a DataGrid_EndCellEdit event that calls the BindingBaseExpression to update but I think the DataGridColumn is ignoring the update option.

(10-12-12)

Still no luck, I tried working with BindingBaseExpression to no avail. Obviously the IMultiValueCOnverter binding is doing something odd.

来源：https://stackoverflow.com/questions/12073597/binding-to-datagridcolumn-with-imultivalueconverter-encounters-issues-while-usin

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