上下文范围异常

Question

我正在用C＃编程，在使用xaml.cs代码隐藏时我遇到了一个非常奇怪的错误。我找到了一个解决方法，但这是一个巨大的黑客攻击：

这不起作用 - 无声地失败。当我输入断点时，当我尝试观察fileList时出现此错误：

“当前上下文中不存在fileList。”

void item_Selected(object sender, RoutedEventArgs e) {

    // Does not work even if on two separate lines.

    IList<string> fileList = new List<string>(); 

    TreeViewItem _item = (TreeViewItem)sender;
    FileName = _item.Tag as string;

    fileList = Directory.GetFiles(FileName, "*.extension").ToList();

    // Other stuff to be done with fileList here, which has not been coded yet.

    OnDirectoryChanged(FileName, EventArgs.Empty);  // Breakpoint here
}

这是有效的黑客：

IList<string> fileList;

void item_Selected(object sender, RoutedEventArgs e) {

    fileList = new List<string>();
    TreeViewItem _item = (TreeViewItem)sender;
    FileName = _item.Tag as string;
    fileList = Directory.GetFiles(FileName, "*.xls?").ToList();

    // Other stuff to be done with fileList here, which has not been coded yet.

    OnDirectoryChanged(FileName, EventArgs.Empty);  // Breakpoint here
}

我想知道的是：为什么？