How to create a simple HMI screen

QuickOPC.NET
Product Version 5.1
Application Note
How to create a simple HMI screen
Update: Starting with version 5.20, the same outcome can be achieved more easily, with the use of Live Binding
(no coding required).
In this article, we will create a Windows Forms application that shows how to use implement an HMI screen by
storing OPC Item IDs in the Tag property of screen controls, and animate the controls by subscribing to all items at
once. We will also show a possibility how to write to an OPC item from the screen.
The first step is to create the form, and place the required controls on it. We will use plain TextBox controls for
simplicity, but you can create much fancier user interfaces by using different and advanced controls and changing
their properties based on OPC data.
We will also place an EasyDAClient non-visual component on the form. This can be done by placing it on the
Toolbox and then dragging from there; please read the Quick Start or Concepts documents for instructions on this.
CODE Consulting and Development, s.r.o. , Bolevecka naves 27, 323 00 Plzen, Czech Republic
e-mail: [email protected], Web: www.opclabs.com, tel. +420 603 214 412, fax +420 378 600 795
QuickOPC.NET-8-How to create a simple HMI screen.docx; 2013-11-21
Page 1 of 4
QuickOPC.NET
Product Version 5.1
Application Note
We will use a "trick" here that allows us to link each control directly to its corresponding OPC item. We will store
the OPC Item ID (a string) in a Tag property of each control that we want to have periodically updated. For
example, for our first text box:
In the Load handler of the form, we will go through all controls on the form. For each control that has non-null Tag,
we will subscribe to OPC item specified by that tag. For performance reasons, it is wise to subscribe to multiple
items at once, so we will first assemble a list "arguments", and then subscribe in a single method call. Each
DAItemGroupArguments object has a State property (the last argument in its constructor) that can be an arbitrary
object; we will pass in a reference to the control being subscribed. This will later allow us to directly update the
control, when a change notification arrives, without having to look it up.
Next, we will write a handler for the ItemChanged event of the EasyDAClient object. This handler will be called for
any significant change in the items we have subscribed to. In the event handler, we will inspect the State property
of the event arguments, and if it corresponds to a TextBox control, we will update its text either by the value that
has arrived (if there was no exception), or by an error text.
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
CODE Consulting and Development, s.r.o. , Bolevecka naves 27, 323 00 Plzen, Czech Republic
e-mail: [email protected], Web: www.opclabs.com, tel. +420 603 214 412, fax +420 378 600 795
QuickOPC.NET-8-How to create a simple HMI screen.docx; 2013-11-21
Page 2 of 4
QuickOPC.NET
Product Version 5.1
Application Note
var argumentsList = new List<DAItemGroupArguments>();
foreach (Control control in Controls)
{
var itemId = control.Tag as string;
if (itemId != null)
argumentsList.Add(new DAItemGroupArguments("",
"OPCLabs.KitServer.2", itemId, 50, control));
}
easyDAClient1.SubscribeMultipleItems(argumentsList.ToArray());
}
private void easyDAClient1_ItemChanged(object sender,
EasyDAItemChangedEventArgs e)
{
var textBox = e.State as TextBox;
if (textBox != null && textBox.ReadOnly)
{
if (e.Exception == null)
textBox.Text = e.Vtq.DisplayValue();
else
textBox.Text =
Resources.Form1_easyDAClient1_ItemChanged____Error___;
}
}
private void writeButton_Click(object sender, EventArgs e)
{
TextBox textBox = writeValueTextBox;
easyDAClient1.WriteItemValue("", "OPCLabs.KitServer.2",
(string)textBox.Tag, textBox.Text);
}
}
The last method in the example allows a communication in the opposite direction, e.g. for process setpoints.
Pressing the "Write" button takes the value entered by the user into the text box, and writes it into an OPC item.
CODE Consulting and Development, s.r.o. , Bolevecka naves 27, 323 00 Plzen, Czech Republic
e-mail: [email protected], Web: www.opclabs.com, tel. +420 603 214 412, fax +420 378 600 795
QuickOPC.NET-8-How to create a simple HMI screen.docx; 2013-11-21
Page 3 of 4
QuickOPC.NET
Product Version 5.1
Application Note
When you run the application, it will show quickly updating values and allow you to perform the Write operation:
This application is fully resistant against network problems, OPC server crashes etc. You do not need to write
any additional code for that! To prove it, find and select the OPC Simulation Server process (opcrtkit.exe) in the
Task Manager, and "kill it" by pressing the "End process" button. You will see that the values on the form
change to an error text. If you, however, wait for some minutes, you will see that the server process restarts
itself (this is caused by the reconnection facility in the QuickOPC component), and valid values appear on the
form again. The reconnection delays can be influenced by setting various properties on EasyDAClient object.
This example project is included with the product. Please use the example from the product itself for the most upto-date code of the example.
CODE Consulting and Development, s.r.o. , Bolevecka naves 27, 323 00 Plzen, Czech Republic
e-mail: [email protected], Web: www.opclabs.com, tel. +420 603 214 412, fax +420 378 600 795
QuickOPC.NET-8-How to create a simple HMI screen.docx; 2013-11-21
Page 4 of 4