不能在密封的局部类中使用外部类

我是使用c#的新手，我正在尝试构建一个简单的windows商店应用程序。但是我不明白为什么找不到ArrayList。在下面的代码中，我尝试在Button_Click_1()函数中使用ArrayList。我收到的错误是"The type or namespace name 'ArrayList' could not be found"，但我使用的是System.Collections，其中包括ArrayList。

using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;
// The Basic Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=234237
namespace Statistics
{
    /// <summary>
    /// A basic page that provides characteristics common to most applications.
    /// </summary>
    public sealed partial class MainPage : Statistics.Common.LayoutAwarePage
    {
        public MainPage()
        {
            this.InitializeComponent();
        }
        /// <summary>
        /// Populates the page with content passed during navigation.  Any saved state is also
        /// provided when recreating a page from a prior session.
        /// </summary>
        /// <param name="navigationParameter">The parameter value passed to
        /// <see cref="Frame.Navigate(Type, Object)"/> when this page was initially requested.
        /// </param>
        /// <param name="pageState">A dictionary of state preserved by this page during an earlier
        /// session.  This will be null the first time a page is visited.</param>
        protected override void LoadState(Object navigationParameter, Dictionary<String, Object> pageState)
        {
        }
        /// <summary>
        /// Preserves state associated with this page in case the application is suspended or the
        /// page is discarded from the navigation cache.  Values must conform to the serialization
        /// requirements of <see cref="SuspensionManager.SessionState"/>.
        /// </summary>
        /// <param name="pageState">An empty dictionary to be populated with serializable state.</param>
        protected override void SaveState(Dictionary<String, Object> pageState)
        {
        }
        private void Button_Click_1(object sender, RoutedEventArgs e)
        {
            ArrayList data = new ArrayList();
        }
        private void TextBox_TextChanged_1(object sender, TextChangedEventArgs e)
        {
        }
    }
}