Communicating with a Thread

[Demian Panello]

Hi!. I wrote an application that start a thread that read some data from the communication port. The problem is that I want to put the data in a textbox, (text1), and I don't know how to do that:confused:. In C++ I just use a global variable, but how can I define a global variable in Visual C#. How can I get data from the thread?. Thank you very much. Demian.

[Judah Gabriel Himango]

Global variables are looked down upon in the object-oriented world, and are not allowed in Java or C#. If you want to place text inside the textbox, just pass your textbox instance to the object reading your communication port. Also note that Windows Forms controls are single threaded in nature; it's a no-no to modify them from a thread other than the thread that owns the handle to the control (ie the thread that the control was created on). Fortunately for you and I, all Windows Forms controls contain a method called .Invoke that lets you call a method on the control using the thread that owns the handle. --------------------------- He who knows that enough is enough will always have enough. -Lao Tsu

[Heath Stewart]

Use Control.InvokeRequired and Control.Invoke from threads other than the thread on which the control was created. Global variables are also not a very good way unless you use good locking when reading/writing from/to them (the lock keyword in C# is a simple way to do this using a monitor). To use a global variable, you can always use a static property or, if your threaded method is a method defined on the Control class that contains your TextBox, just use a private variable (and be sure to lock it). To write to the text box, make sure your thread class or procedure has a reference to your TextBox (for example, you could thread a single method in your class which contains the TextBox reference). If you're not sure if your method would be threaded or not, use the code below (otherwise eliminate the check for Control.InvokeRequired):

private void ReadFromPort()
{
string value = value from port;
if (text1.InvokeRequired)
{
// This isn't really optimized, but it's only an example...
Type t = text1.GetType();
MethodInfo info = t.GetProperty("Text").GetSetMethod();
Delegate d = Delegate.CreateDelegate(t, info);
text1.Invoke(d, new object[] {value});
}
else text1.Text = value;
}

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[SapiensBwG]

sorry judah didnt get that last part! could u exemplify! thx in advance i was needing this for another app

[Judah Gabriel Himango]

See Heath's post below. --------------------------- He who knows that enough is enough will always have enough. -Lao Tsu

[Judah Gabriel Himango]

Keeping in mind that was example code, FYI that snippet won't work; Delegate.CreateDelegate takes a Type parameter for delegate types only. You might want to try this instead:

private delegate void SetTextDelegate(TextBox tb, string text);

private void ReadFromPort(TextBox tb)
{
string portData = ... // read from communications port

   this.SetText(tb, portData);

}

private void SetText(TextBox tb, string text)
{
if(tb.InvokeRequired) // if we're calling from any thread other than the one used to create the text box
{
tb.Invoke(new SetTextDelegate(SetText), new object[] {tb, text});
}
else tb.Text = text; // no invoke required
}

I *think* that should work. :) --------------------------- He who knows that enough is enough will always have enough. -Lao Tsu

[SapiensBwG]

thx for the help guys appreciate it

[Demian Panello]

Hi Lao. Thank you for you help. But, the thread method is the method that read the comm. port, so can I pass a parameter to it?, a parameter like TextBox tb?. That method is in another class, no in the class that holds the textbox, and should I pass every control as parameter that I want to write, (with data from the comm port)?. Thank you again for your time. Demian.

[Demian Panello]

The code works fine. But I must pass a textbox reference to the class constructor. And this is a very particular case, 'cause I don't know how many controls I will have, to show the data that the thread read from the comm port. Thank you Judah. Demian.

[Heath Stewart]

This is only if your thread method is in a different class. More than likely, there's no need to do that. In both Judah's and my examples, we assumed the method that will be invoked in another thread was part of the same class, so it already has a reference to the TextBox. This is preferred unless you have some good reason for changing it. If you do, then create a new instance of another class - passing the TextBox reference into the constructor - and start a thread on a method of that class. This is unnecessary, though, because you're creating another class just to run a method in another thread? Why go to the trouble if you don't have to.

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[Demian Panello]

Hi! Well, I have a class hierarchy, and theses classes must keep a communication "alive" with a devices pluged in the comm port. The device, if it has no heceived a command stop the communication. That is the trouble, the thread method is a method deep int the hierarchy. Thank you for your time. Demian.

[Heath Stewart]

Like I said, then, either pass the TextBox reference into the class's constructor or set a property before you start the thread on a method of that class.

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[Demian Panello]

Hi. Yes, that works, but there's no relation between the classes hierarchy and a control as reference in a constructor or in a property. Theses are communication protocol classes, it's so weird to find a control reference in their definitions. I loss the essence of the class hierarchy just putting a textbox in the definitions. That's the problem. Thank you very much for your feedback. Demian.