CODEWITHSUNDEEP
c#wpfmultithreadingvisual-studiotask
Guilherme
Guilherme

Reputation: 37

Write on textbox in a thread (TASK) in WPF Application

I have a program (In WPF Application) which receive by a thread info from COM port. Here's part from that:

static async Task ReceiveData(SerialPort port)
    {
       try
            {
                Thread.Sleep(50);  // Time for read works
                await port.BaseStream.ReadAsync(buffer, 0, 55);  //Wait recive data from Serial Port

                textBox.AppendText("Test");
            }           
    }

The problem occurs because it can be write in the text box just in this task. I have a lot of others textBox outside and works just fine. The error who show is:

An object reference is required for the non-static field, method, or property 'MainWindow.textBox'

If I change the task for public the error disappears but when I build the program the text don't appear on the box.

I know the message it's about reference but it seems this part is OK, I think it's something about turn the textBox in public access.

I change the code just for:

async Task ReceiveData(SerialPort port)

And the following error appears on output:

Exception thrown: 'System.InvalidOperationException' in WindowsBase.dll

And the error is: ""The calling thread cannot access this object because a different thread owns it.""

---------- SOLVED BY @BrandonKramer ---------- Using:

 Dispatcher.BeginInvoke((Action)(() => textBox.AppendText("Test")));

Upvotes: 1

Views: 6236

Answers (1)

Brandon Kramer
Brandon Kramer

Reputation: 1118

Your error is because UI elements, such as a TextBox, can only be modified from the UI thread.

In order to fix this issue, change:

textBox.AppendText("Test");

to

Dispatcher.BeginInvoke((Action)(() => textBox.AppendText("Test")));

This will cause textBox.AppendText("Test"); to be executed on the UI thread, rather then the background thread that your task is executing on.

Upvotes: 6

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