New to C# - problems with link labels and functions

Question

I am brand new to C# and have previously only written programs in JavaScript, so go easy on me !

I have written an "app launcher" program which reads a text file line by line. Each line is just a path to a program e.g. C:\Users\Jim\Desktop\Gravity.exe

So far, my program can successfully read each line and produce a list of links. As intended, each link appears as the path itself.

The problem I am having is that these links will not work. However they WILL work if they are all just given the same fixed path. I would like each link to use its .Text property as the destination. (please see the comments "works" and "does not work" in my code below). The only error I get is "cannot find the file specified".

I would really appreciate any help on this as I am finding C# a lot harder than Javascript !

public partial class Form1 : Form
{
    private void Form1_Load(object sender, EventArgs e)   //on form load
    {
        int counter = 0;
        string line;
        string myfile = @"c:\users\matt\desktop\file.txt";

        // Read the file and display it line by line.
        System.IO.StreamReader file = new System.IO.StreamReader(myfile);
        while ((line = file.ReadLine()) != null)
        {
            //MessageBox.Show(line);   //check whats on each line

            LinkLabel mylinklabel = new LinkLabel();        //LinkLabel tells us the type of the object   e.g.  string mystring ="hello";
            mylinklabel.Text = line;
            this.Controls.Add(mylinklabel);
            mylinklabel.Location = new Point(0, 30 + counter * 30);

            mylinklabel.Click += new System.EventHandler(LinkClick);

            counter++;
        }
        file.Close();
    }

    private void LinkClick(object sender, System.EventArgs e)
    {
        //Process.Start(this.Text);  //doesn't work
        Process.Start(@"C:\Users\Jim\Desktop\gravity.exe");   //works
    }        
}

Update:

Thank you for your comments guys. I have changed the line in question to:

Process.Start(((LinkLabel)sender).Text);

... and it does indeed work. But perhaps I could ask a question about this line, as I am finding the syntax a little unusual and confusing.

Isn't sender a property of the LinkLabel object? So to reference it, shouldn't we use LinkLabel.sender? (this would be more JavaScript style ! I don't understand the (LinkLabel)sender notation)

I also do not understand:

private void LinkClick(object sender, System.EventArgs e)

What does a space mean? Such as between object and sender? Or between System.EventArgs e? LinkClick is the name of the event, but why do we have two things here, separated by a comma?

As you can tell, I am currently finding the C# syntax a bit hard going!

Thank you in advance.

@user: Welcome to StackOverflow, but FYI, StackOverflow is a Q&A site, not a discussion forum, so we don't use "Hi", or "Thanks", or signatures. — John Saunders, May 02 '11 at 18:43
@user What you need is a tutorial on C#. After that things should be much clearer to you. — dandan78, May 04 '11 at 11:47

score 3 · Answer 1 · answered May 02 '11 at 18:41

Your use of this.Text appears to be at least one of the problems.

this refers to the current instance of your class. What you want is the instance of the LinkLabel that was clicked. Fortunately, the event's sender argument provides this information.

So try something like this instead.

LinkLabel lnk = sender as LinkLabel;
System.Diagnostics.Process.Start(lnk.Text);

score 0 · Answer 2 · answered May 02 '11 at 18:41

0

In that context "this.Text" refers to your FORMS text caption. User ((LinkLabel)sender).Text

answered May 02 '11 at 18:41

asawyer

17,642
8
59
87

score 0 · Answer 3 · answered May 02 '11 at 18:43

0

private void LinkClick(object sender, System.EventArgs e)
{
    LinkLabel ll = (LinkLabel)sender;
    System.Diagnostics.Process.Start(ll.Text);
}

answered May 02 '11 at 18:43

Thomas Levesque

286,951
70
623
758

score 0 · Answer 4 · answered May 02 '11 at 18:47

This example tells you better way to achieve this.

http://msdn.microsoft.com/en-us/library/system.windows.forms.linklabel.linkclicked%28v=VS.100%29.aspx

 private void linkLabel1_LinkClicked(object sender, System.Windows.Forms.LinkLabelLinkClickedEventArgs e)
    {
        // Determine which link was clicked within the LinkLabel.
        this.linkLabel1.Links[linkLabel1.Links.IndexOf(e.Link)].Visited = true;

        // Display the appropriate link based on the value of the 
        // LinkData property of the Link object.
        string target = e.Link.LinkData as string;

        // If the value looks like a URL, navigate to it.
        // Otherwise, display it in a message box.
        if(null != target && target.StartsWith("www"))
        {
            System.Diagnostics.Process.Start(target);
        }
        else
        {    
            MessageBox.Show("Item clicked: " + target);
        }
    }

New to C# - problems with link labels and functions

4 Answers4