使用Button抛出NullReferenceException; 我错过了什么吗？

Question

我收到了一个错误Object reference not set to an instance of an object.我想我不会初始化一些东西.

这是代码; 错误在线if (btn.Background.Equals(new SolidColorBrush(Color.FromArgb(0, 0, 0, 0)))):

private void vbOpenGuiaMaestro_Tapped(object sender, TappedRoutedEventArgs e)
{
    Button btn = default(Button);
    if (btn.Background.Equals(new SolidColorBrush(Color.FromArgb(0, 0, 0, 0))))
    {
         btn.Background = materiaColor;
         btn.Foreground = new SolidColorBrush(Color.FromArgb(255, 255, 255, 255));
         stckTeachersGuideClosed.Visibility = Visibility.Visible;
         stckTeachersGuideOpened.Visibility = Visibility.Collapsed;
    }
    else
    {
         btn.Background = new SolidColorBrush(Color.FromArgb(0, 0, 0, 0));
         btn.Foreground = new SolidColorBrush(Color.FromArgb(255, 140, 140, 140));
    }
 }

Answer 1

default(Button)

给你null的Button是一个引用类型.我想你想要的

Button btn = (Button)sender;