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Find character string within line from textfile

Posted on 2016-08-03
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Last Modified: 2016-08-04
Using a windows application form, I am trying to read a text file and find if a string pattern he text file.
I am receiving the error:  Cannot implicitly convert type 'System.Threading.Tasks.Task<string>' to 'string[]'


    public partial class Form1 : Form
    {
        String line;
        StringBuilder sb = new StringBuilder();
        String[] lines;

        public Form1()
        {
            InitializeComponent();
        }

        private async void button1_Click(object sender, EventArgs e)
        {          
            try
            {
                using (StreamReader sr = 
                    new StreamReader(@"\\test.txt"))
                {
                    lines = sr.ReadToEndAsync(); //line where error points to ...
                    foreach(String line in lines)
                    {
                        if (line.Contains("902"))
                        {
                            sb.Append(line);
                        }
                    }                    
                    textBox1.Text = sb.ToString();
                }
            }
            catch (Exception)
            {
                textBox1.Text = "Could not read the file";
                //throw;
            }
        }
    }

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Question by:Scarlett72
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3 Comments
 
LVL 44

Accepted Solution

by:
zephyr_hex (Megan) earned 1200 total points
ID: 41741165
sr.ReadToEndAsync() is returning something of type Task<string>
lines is defined as String[]

Try defining lines as
var lines = new List<Task>();

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And then add the task to the list:
lines.Add(sr.ReadToEndAsync());

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So your code would look like:
 public partial class Form1 : Form
    {
        String line;
        StringBuilder sb = new StringBuilder();
        var lines = new List<Task>();
        //... other stuff

        {
                    lines.Add(sr.ReadToEndAsync()); //line where error points to ...
        //... other stuff

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1
 
LVL 30

Assisted Solution

by:anarki_jimbel
anarki_jimbel earned 800 total points
ID: 41741695
Really Zephyr_hex explained what the error was but I'd like to clarify.
The problem is that ReadToEndAsync method returns a Task containing a string.
And as your error says you cannot assign this Task to a string array.
However, according to MS you may assign it to a string, something like below (see https://msdn.microsoft.com/en-us/library/dd321468(v=vs.100).aspx):

string s="";
if(task1.IsReady())
s = task1.Result;

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When you have a string representing your file ('s' above) content you may split it to an array or whatever by new line delimiters, if you need, of course.

Also, do you really need asynchronous read?
Just in case, check https://msdn.microsoft.com/en-us/library/system.io.streamreader.readtoendasync(v=vs.110).aspx and
https://msdn.microsoft.com/en-us/library/system.io.streamreader.readtoend(v=vs.110).aspx
1
 

Author Closing Comment

by:Scarlett72
ID: 41742565
Thank you both zephyr and anarki.  You've helped me understand the concepts a little better.
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