为什么以及如何摆脱NullReferenceException

Question

namespace WindowsPhoneApp
{

    Class MainPage()
    {
        private void ProcentSlider_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
        {
            ShowSliderValue.Text = ProcentSlider.Value.ToString(); //<-- NullReferenceException
        }

    }
}

我无法将Slider控件的值引用到TextBox控件...

Answer 1

试试这个 - 可能是因为ShowSliderValue在不同的线程中运行..但是有点猜测。

private void ProcentSlider_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
{
    Dispatcher.BeginInvoke(new Action(() => ShowSliderValue.Text = ProcentSlider.Value.ToString();));
}

或者也许这个？

private void ProcentSlider_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
{
    var slider = (ProcentSlider)sender;
    ShowSliderValue.Text = slider.Value.ToString();
}