Cross thread Exception

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hello
i have a main FORM. in this form, users enter their username and password and then log in to system... a have a DatabaseConnection class which responsible for any database connection. here is my problem:
when program try to connect to database, my FORM freez and any update cant has effect until database operations finished. i have a PicturBox1 and i want to set its visibility to TRUE immediately after i click logIn button. i dedicated a thread for my purpose of UPDATING GUI, but i see Cross-thread Exception....
I spend lots of time on the net but cant find my answer yet. oh, of course i apologize for my poor English, because English isn't my first language.

anywhere here is my code:

private void login_Click(object sender, EventArgs e)
{

Thread t = new Thread(new ThreadStart(test));
t.Start();
DB = new DatabaseConnection();

}
public void test()
{
pictureBox1.Visible = true;

}
Is it possible for you to give me an exact solution to this problem?
Thanks in advance for your attention
have a nice day
Best Regards,hamed

Posted 13-Jul-13 1:56am

hamed1991

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[no name] 13-Jul-13 8:56am

What do you mean you could not find this? There are examples of this AND the solutions all over the web. You cannot access UI controls from a thread that did not create them, the UI thread. It's that simple. You need to call the Invoke method. http://msdn.microsoft.com/en-us/library/system.windows.forms.picturebox.invoke.aspx

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Ravimal Bandara · Answer 1 · 2013-07-13T02:57:00

This exception is thrown when you try to access controls from a thread other than the one it was created. To access controls and controls' properties use delegate. Its easy.

C#

delegate void updatePictureBoxDelegate();
private void updatePictureBoxVisibilityTrue()
{
 if (pictureBox1.InvokeRequired)
 {
     // this is worker thread
     updatePictureBoxDelegate del = new        updatePictureBoxDelegate(updatePictureBoxVisibilityTrue);
     pictureBox1.Invoke(del, null);
 }
 else
 {
     // this is UI thread
     pictureBox1.Visible = true;
 }
}

call "updatePictureBoxVisibilityTrue" from your thread instead of "test" method.

User 8696850 · Answer 2 · 2013-07-13T03:15:00

Solution 2

try to use a backgrounworker :

link[^]

before calling the sync method show the picture then in the do work of the background worker put the connection to database and all the function that take a lot of time then when background worker completed hide the picture

Posted 13-Jul-13 3:15am

User 8696850