绑定按钮IsEnabled取决于组合框选择

Question

I'm sure this is really easy, but I don't know how do it. I have a ComboBox and a Button, and I need to have the Button enabled only if the ComboBox has an item selected, ie if in the ComboBox has no elements showing, then the Button must be disabled. How can I do this?

I have tried doing the following:

IsEnabled="{Binding ElementName=mycombobox, Path=SelectedIndex}"/>

But it does not work. I'm using Silverlight 5.

Thanks in advance

Answer 1

可能有一种更有效的方法，但我只需要确定SelectedIndexChanged事件中ComboBox.SelectedItem是否为null。

Answer 2

MSDN has something that may be of help to you here . It suggests you use a converter or a data trigger. I haven't tested this, but perhaps this will work?

<Window.Resources>
    <Style x:Key="MyButtonStyle" TargetType="{x:Type Button}">
        <Setter Property="IsEnabled" Value="True"/>
        <Style.Triggers>
            <DataTrigger Binding="{Binding Path=SelectedItem, ElementName=comboBox1}" Value="{x:Null}">
                <Setter Property="UIElement.IsEnabled" Value="False"/>
            </DataTrigger>
        </Style.Triggers>
    </Style>
</Window.Resources>

<Grid>
    <ComboBox Name="comboBox1">
        <ComboBoxItem>One</ComboBoxItem>
        <ComboBoxItem>Two</ComboBoxItem>
        <ComboBoxItem>Three</ComboBoxItem>
    </ComboBox>

    <Button Style="{StaticResource MyButtonStyle}" Name="myButton" Content="Push me"/>
</Grid>

EDIT

I am under the impression that Cyndy has already figured all this out, but for any future readers...

As noted in the comments, you cannot do DataTriggers in Silverlight. You'll need to do a converter. Here is another post that may help. In essence, you'll need to have your XAML set something like:

<Button Content="MyButton" IsEnabled="{Binding SelectedItem, ElementName=comboBox1, Converter={StaticResource myConverter}}"/>

and then in your code-behind, you'll need something like:

public class MyConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return !(value == null);
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}