如何为ToolStripMenuItem项目数组创建实例？

Question

In top of form1:

ToolStripMenuItem[] items;

In constructor:

for (int i = 0; i < items.Length; i++)
{
    items[i] = new ToolStripMenuItem();
    recentFilesToolStripMenuItem.DropDownItems.AddRange(items);
}

if (!File.Exists(@"e:\RecentFiles.txt"))
{
    recentfiles = new StreamWriter(@"e:\RecentFiles.txt");
    recentfiles.Close();
}
else
{
    lines = File.ReadAllLines(@"e:\RecentFiles.txt");
}

Before it i used single item and i made one instance for it in the top of form1. But i want to add to the DropDownItems array of items. And i don't how many items i want for it to be unlimited.

Then i have this event:

private void recentFilesToolStripMenuItem_MouseEnter(object sender, EventArgs e)
{
    for (int i = 0; i < lines.Length; i++)
    {
        items[i].Text = lines[i];
    }            
}

When i used a single item i just did in the MouseEnter event:

item.Text = "hello world";

But now i want to add the items from the text file it can be 1 items or 200 items the problem is that items are null in the constructor.

I did now in the constructor changed it to:

if (!File.Exists(@"e:\RecentFiles.txt"))
{
    recentfiles = new StreamWriter(@"e:\RecentFiles.txt");
    recentfiles.Close();
}
else
{
    lines = File.ReadAllLines(@"e:\RecentFiles.txt");
    items = new ToolStripMenuItem[lines.Length];
}

In this case lines.Length is 3. But now when i look on items i see 3 items that each one of them is null. So i know how many items i need to instance but for some reason they are all null.

Answer 1

It seems, that your main problem is in the fact that you don't know in advance the length of items[] ; such problem is a good task for Linq , something like that:

  private ToolStripMenuItem[] items;

  ...

in the constructor:

  items = File
    .ReadLines(@"e:\RecentFiles.txt")
    .Select(line => new ToolStripMenuItem() {
       Text = line
     })
    .ToArray();
  ...
  // if items are used in AddRange only
  // you have no need neither of ToArray() nor in private field
  recentFilesToolStripMenuItem.DropDownItems.AddRange(items);

in case you want, say, 10 first recent files only:

  items = File
    .ReadLines(@"e:\RecentFiles.txt")
    .Take(10)
    .Select(line => new ToolStripMenuItem() {
       Text = line
     })
    .ToArray();