为什么此WPF滑块会引发异常？

Question

Code:

private void slider1_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
        {
            updateTickCounter(slider1.Value);
        }

        private void updateTickCounter(double value)
        {
            tickCounter.Content = value.ToString();
        }

XAML:

<Slider Height="32" HorizontalAlignment="Right" Margin="0,21,61,0" Name="slider1" VerticalAlignment="Top" Width="200" IsSnapToTickEnabled="True" Orientation="Horizontal" TickFrequency="1" TickPlacement="BottomRight" Value="1" Minimum="1" Maximum="10" ValueChanged="slider1_ValueChanged" />

I'm trying to have a slider that starts at value 1 out of 10. Every time the slider is moved I want a label called 'tickCounter' to change text.

The code above throws an exception when ran -- "Object reference not set to an instance of an object."

However, once I change both the values of "Value" and "Minimum" in XAML it works fine. It's as if I can't make it not start at zero. It's really weird. Any help?

Answer 1

如果我查看提供的堆栈跟踪，那么我唯一可能的nullexception似乎是tickCounter == null

Answer 2

Rather than using events to update the label, use DataBinding .

<Slider Name="slider1" IsSnapToTickEnabled="True" Orientation="Horizontal" Value="1" Minimum="1" Maximum="10" />

<Label Name="tickCounter" Content="{Binding Path=Value, ElementName=slider1"} />

Also, if you do not need any of the additional abilities of a Label you should use a TextBlock .

<TextBlock Name="tickCounter" Text="{Binding Path=Value, ElementName=slider1"} />