RadioButton Checked事件发生错误

Question

Here is xaml codes for your testing needs.

<Window x:Class="MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="200" Width="325">
<Grid>
    <RadioButton x:Name="RadioButton1" IsChecked="True" GroupName="MyGroup" Content="Select" Margin="0,10,0,0"/>
    <RadioButton x:Name="RadioButton2" GroupName="MyGroup" Content="Select" Margin="0,30,0,0"/>
    <Menu x:Name="Menu1" HorizontalAlignment="Left" Margin="0,50,0,0">
        <MenuItem x:Name="MenuItem1" Header="Saving">
            <MenuItem x:Name="MenuItem2" Header="Save"/>
            <MenuItem x:Name="MenuItem3" Header="Don't save"/>
        </MenuItem>
    </Menu>
</Grid>
</Window>

Following code is working great.

Class MainWindow 
Private Sub RadioButton1_Unchecked(sender As Object, e As RoutedEventArgs) Handles RadioButton1.Unchecked
    Menu1.IsEnabled = False
End Sub
End Class

Following code is not working. Do you know why?

Class MainWindow 
Private Sub RadioButton1_Checked(sender As Object, e As RoutedEventArgs) Handles RadioButton1.Checked
    Menu1.IsEnabled = True
End Sub
End Class

Error picture:

Answer 1

Because your RadioButton node is above from the Menu node. The Checked event will occur before Menu1 created. You have to check the Menu1 is not null .

if (null != Menu1)
    Menu1.IsEnabled = true;

And place IsEnabled="True" to Menu node for default state.

<Menu x:Name="Menu1" IsEnabled="True" HorizontalAlignment="Left" Margin="0,50,0,0">