DataContext System.NullReferenceException c＃xaml

Question

我嘗試從Msdn實現一個示例，但是發生了空引用異常，我不知道為什么：這是Mainpage.xaml.cs文件的C＃代碼：

     // Create an instance of the MyColors class 
        // that implements INotifyPropertyChanged.
        MyColors textcolor = new MyColors();

        // Brush1 is set to be a SolidColorBrush with the value Red.
        textcolor.Brush1 = new SolidColorBrush(Colors.Red);

        // Set the DataContext of the TextBox MyTextBox.
        MyTextBox.DataContext = textcolor; //HERE THE ERROR OCCURS!

        // Create the binding and associate it with the text box.
        Binding binding = new Binding() { Path = new PropertyPath("Brush1") };
        MyTextBox.SetBinding(TextBox.ForegroundProperty, binding);

這是后面的xaml代碼：

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <TextBox x:Name="MyTextBox" Text="Text" Foreground="{Binding Brush1}"/>
</Grid>

Answer 1

如注釋中所述，如果您在Window的構造函數中引用MyTextBox ，則需要在調用InitializeComponent()並生成XAML的樹之后執行此操作

InitializeComponent();

MyColors textcolor = new MyColors();
textcolor.Brush1 = new SolidColorBrush(Colors.Red);
MyTextBox.DataContext = textcolor;