Read file in memory and then invoke a richtextbox

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2.50/5 (2 votes)

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So I am having a difficult problem:
Form1=> added a progress bar
Form2 => added a background worker
In the DoWork, I want to read a file into memory, than send that file to open in a richtextbox from Form2.

I am getting an error : "Cross-thread operation not valid: Richtextbox accessed from a thread other than the thread it was created on"

So, I searched google, and found put that I need to invoke the rochtextbox..

can you please help?
This is my code till now:

C#

void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {

            // Your background task goes here
            for (int i = 0; i <= 100; i++)
            {
                // Report progress to 'UI' thread
                backgroundWorker1.ReportProgress(i);

                string path = "articles\\" + name + ".dat";
                try
                {
                    using (FileStream fileStream = File.OpenRead(path))
                    {
                        MemoryStream memStream = new MemoryStream();
                        memStream.SetLength(fileStream.Length);
                        fileStream.Read(memStream.GetBuffer(), 0, (int)fileStream.Length);
                    }
                    richTextBox1.Invoke(new MethodInvoker(delegate { name1 = richTextBox1.Text; }));
//
                    this.richTextBox1.LoadFile(path, RichTextBoxStreamType.RichText);
                    this.richTextBox1.ReadOnly = true;
                }
                catch (Exception ee)
                {
                    Console.WriteLine(ee.Message);
                }
  

            }
        }

Posted 8-Apr-13 10:10am

Luci C

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Comments

S@53K^S 8-Apr-13 16:13pm

Did you try creating a global string variable and send the content of the file to that variable?

Luci C 8-Apr-13 16:14pm

i have formatted text and images in the file... And sometimes files get bigger than 100 mb..
I don't know if all my code is correct

S@53K^S 8-Apr-13 16:24pm

How are you planning to dump all the binary data into a richtextbox if it is mixed like images and text ? and the trick is to run progress bar in separate thread and do all the file reading and assigning to rich text box on the main thread

Luci C 8-Apr-13 16:26pm

reading it's done very well with "Load file" method, but i do not know how can I animate the progressbar while it loads the file...
so I thought I have to put it into memory and then send it to the richtextbox..

Alan N 8-Apr-13 18:50pm

As no one else has asked I will. Why do you
1) Read the file into a memorystream 100 times and then do nothing with it
2) Copy the RichTextBox.Text to a variable 100 times
3) Load the RichTextBox directly from the file 100 times

3 solutions

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Clifford Nelson · Answer 1 · 2013-04-08T10:18:00

Solution 1

TPL is the easest:

XML

Task<FxMaintenanceChildViewModel> task = Task.Factory.StartNew<strReturn>((stateObj) =>
    {
        // Get the data here
        return strReturn;
    }, null);
task.ContinueWith(rtn =>
    {
       //put string into 
       richTextBox1.Text = rtn;
    }, UiScheduler);

Posted 8-Apr-13 10:18am

Clifford Nelson

Comments

Luci C 8-Apr-13 16:23pm

didn't understand too much... so you say i must run tasks in parallel

Clifford Nelson 8-Apr-13 17:14pm

What happens is that the first part would read the text into memory, the second continues after the task has completed, and, if you are on the UI thread when you start, you will be on the UI thread when the task completes. Besides possilby Async, this is actually quite easy.

Luci C 8-Apr-13 17:22pm

ok, understood...but what are these "FxMaintenanceChildViewModel"and UIScheduler?
what do I have to include?

Clifford Nelson 8-Apr-13 22:29pm

Forgot to clean that stuff out. Just replace with var. Should have been strReturn

Sergey Alexandrovich Kryukov · Answer 2 · 2013-04-08T10:30:00

The problem is here:

C#

this.richTextBox1.LoadFile(path, RichTextBoxStreamType.RichText);
this.richTextBox1.ReadOnly = true;

These two lines should be in a method invoked via System.Windows.Forms.Control.Invoke.

You cannot call anything related to UI from non-UI thread. Instead, you need to use the method Invoke or BeginInvoke of System.Windows.Threading.Dispatcher (for both Forms or WPF) or System.Windows.Forms.Control (Forms only).

You will find detailed explanation of how it works and code samples in my past answers:
Control.Invoke() vs. Control.BeginInvoke()[^],
Problem with Treeview Scanner And MD5[^].

See also more references on threading:
How to get a keydown event to operate on a different thread in vb.net[^],
Control events not firing after enable disable + multithreading[^].

Also, previous two lines make no sense. Your invoked method does nothing, and you read the content of the file stream to memory stream, which makes no sense. You really need a string to be assigned to the string property RichTextBox.Rtf, so you need to read to the char[] buffer, convert it to string and assign.

Besides, the whole activity with the thread won't help you to avoid some UI freezing much, because most of the time will be spent not on reading of the file, but on the assignment of Rtf value to the control, as the changes should be rendered. So, practically, it would be better to read the RTF file by the control itself in the UI thread.

—SA

Sergey Alexandrovich Kryukov · Answer 3 · 2013-04-08T10:50:00

Luci C wrote:
Form 1 is MDIParent and it show up Form2 which is an mdichild. On the Form2 I have a link-> which opens Form3 with some content read from file.

Here is the idea: who needs MDI, ever? Why torturing yourself and scaring off your users?
Do yourself a great favor: do not use MDI at all. You can do much easier to implement design without it, with much better quality. MDI is highly discouraged even by Microsoft, in fact, Microsoft dropped it out of WPF and will hardly support it. More importantly, you will scare off all your users if you use MDI. Just don't. Please see:
http://en.wikipedia.org/wiki/Multiple_document_interface#Disadvantages[^],
How to Create MDI Parent Window in WPF?[^].

I can explain what to do instead. Please see my past answers:
How to Create MDI Parent Window in WPF? [Solution 2],
Question on using MDI windows in WPF[^],
MDIContainer giving error[^],
How to set child forms maximized, last childform minimized[^].

—SA