Textbox输入状态提示

前：

 <DockPanel Margin="10">
            <TextBox SelectionChanged="TextBox_SelectionChanged" DockPanel.Dock="Top" />
            <TextBox Name="txtStatus" AcceptsReturn="True" TextWrapping="Wrap" IsReadOnly="True" />

        </DockPanel>

后：

        private void TextBox_SelectionChanged(object sender, RoutedEventArgs e)
        {
            TextBox textBox = sender as TextBox;
            txtStatus.Text = "Selection starts at character #" + textBox.SelectionStart + Environment.NewLine;
            txtStatus.Text += "Selection is " + textBox.SelectionLength + " character(s) long" + Environment.NewLine;
            txtStatus.Text += "Selected text: '" + textBox.SelectedText + "'";
        }