单击TreeNode时发生未处理的"System.NullReferenceException"类型的异常

Question

每当点击treenode时,我都会收到此错误消息:

Picture-Resize.exe中发生类型为"System.NullReferenceException"的未处理异常附加信息:对象引用未设置为对象的实例.

我的代码如下:

public Form1()
{
    InitializeComponent();
    this.treeView1.NodeMouseClick += new TreeNodeMouseClickEventHandler (this.treeView1_NodeMouseClick);
    PopulateTreeView();
}

private void PopulateTreeView()
{
   TreeNode rootNode;

   DirectoryInfo info = new DirectoryInfo(@"c:\\");
   if (info.Exists)
   {
       rootNode = new TreeNode(info.Name);
       rootNode.Tag = info;
       GetDirectories(info.GetDirectories(), rootNode);
       treeView1.Nodes.Add(rootNode);
   }
}

private void GetDirectories(DirectoryInfo[] subDirs, TreeNode nodeToAddTo)
{
   TreeNode aNode;
   DirectoryInfo[] subSubDirs;
   foreach (DirectoryInfo subDir in subDirs)
   {
       aNode = new TreeNode(subDir.Name, 0, 0);
       aNode.Tag = subDir;
       aNode.ImageKey = "folder";
       try
       {
           /*  subSubDirs = subDir.GetDirectories();
             if (subSubDirs.Length != 0)
             {
                 GetDirectories2(subSubDirs, aNode);
             }*/
       }
       catch (System.UnauthorizedAccessException)
       {
           subSubDirs = new DirectoryInfo[0];
       }
       nodeToAddTo.Nodes.Add(aNode);
   }
}


void treeView1_NodeMouseClick(object sender, TreeNodeMouseClickEventArgs e)
{               
   //if (treeView1.SelectedNode.Nodes.Count > 0) { MessageBox.Show("Child node exists"); } else { MessageBox.Show("Child Node does not exist"); }

   try
   {
       TreeNode newSelected = e.Node;
     //  treeView1.SelectedNode.Nodes.Add("test");

       listView1.Items.Clear();
       DirectoryInfo nodeDirInfo = (DirectoryInfo)newSelected.Tag;
       ListViewItem.ListViewSubItem[] subItems;

       ListViewItem item = null;

       foreach (DirectoryInfo dir in nodeDirInfo.GetDirectories())
       {
           item = new ListViewItem(dir.Name, 0);
           subItems = new ListViewItem.ListViewSubItem[]
            {new ListViewItem.ListViewSubItem(item, "Directory"), 
             new ListViewItem.ListViewSubItem(item, 
                dir.LastAccessTime.ToShortDateString())};
           item.SubItems.AddRange(subItems);
           listView1.Items.Add(item);
       }
       foreach (FileInfo file in nodeDirInfo.GetFiles())
       {
           item = new ListViewItem(file.Name, 1);
           subItems = new ListViewItem.ListViewSubItem[]
            { new ListViewItem.ListViewSubItem(item, "File"), 
             new ListViewItem.ListViewSubItem(item, 
                file.LastAccessTime.ToShortDateString())};

           item.SubItems.AddRange(subItems);
           listView1.Items.Add(item);
       }

       listView1.AutoResizeColumns(ColumnHeaderAutoResizeStyle.HeaderSize);
   }
   catch (Exception ex)
   {
        if (ex is System.NullReferenceException || ex is System.UnauthorizedAccessException)
        {
        }
   }
}

异常处理程序捕获它会发生什么,但由于抛出异常,它需要用户单击两次才能使单击处理程序生效.

为什么我会收到此错误,我该如何避免？

Answer 1

您需要调试代码.

我假设您使用的是Visual Studio,如果是,请执行以下操作:

1. 转到"调试"菜单.
2. 单击Exceptions ...选项.
3. 应出现以下对话框:

请注意选中Common Language Runtime Exceptions复选框.

单击"确定"后,现在当您的代码或.NET Framework抛出异常时调试代码时,调试器将在引发异常的行上停止.这使得找到某些东西"破坏"的地方变得更加容易.