I'm trying to build a GUI for my application. I'm stuck on one problem. I try to use timer "OnTImedEvent" to call my function to update the chart. Unfortunately, MVS gives me a "Cross-thread operation not valid". I've came across some tips, regarding something called delegate but I can't manage to get it working. Since I'm nooby in windowsFormsApp (started today) I'm asking for your help. Here's my code:
using System;
using System.IO.Ports;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Timers;
namespace WindowsFormsApp1
{
public partial class Form1 : Form
{
bool state = false;
private static System.Timers.Timer timer;
public Form1()
{
InitializeComponent();
timer = new System.Timers.Timer(10);
timer.Elapsed += OnTimedEvent;
timer.AutoReset = true;
timer.Enabled = true;
}
private void button1_Click(object sender, EventArgs e)
{
if (serialPort1.IsOpen)
{
serialPort1.WriteLine("a\n");
}
else
MessageBox.Show("Brak połączenia z urządzeniem");
}
private void button4_Click(object sender, EventArgs e)
{
if (serialPort1.IsOpen)
{
Form2 form2 = new Form2(serialPort1);
form2.Show();
}
else
MessageBox.Show("Brak połączenia z urządzeniem");
}
private void Form1_Load(object sender, EventArgs e)
{
string[] ports = SerialPort.GetPortNames();
comBoxPort.Items.AddRange(ports);
}
private void btnCon_Click(object sender, EventArgs e)
{
if (state)
{
state = false;
btnCon.ForeColor = Color.Red;
try
{
serialPort1.Close();
}
catch (Exception ex)
{
MessageBox.Show(ex.Message, "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
throw;
}
}
else
{
state = true;
btnCon.ForeColor = Color.Green;
try
{
serialPort1.PortName = comBoxPort.Text;
serialPort1.Open();
}
catch (Exception ex)
{
MessageBox.Show(ex.Message, "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
throw;
}
}
}
private void btnRoll_Click(object sender, EventArgs e)
{
if (serialPort1.IsOpen)
{
serialPort1.WriteLine("s\n");
}
else
MessageBox.Show("Brak połączenia z urządzeniem");
}
private void btnYAW_Click(object sender, EventArgs e)
{
drawChart();
if (serialPort1.IsOpen)
{
serialPort1.WriteLine("d\n");
}
//else
//MessageBox.Show("Brak połączenia z urządzeniem");
}
private void drawChart()
{
chart1.Series["PITCH"].Points.AddY(21);
chart1.Series["ROLL"].Points.AddY(122);
chart1.Series["YAW"].Points.AddY(13);
}
public delegate void drawChartCallback();
private void chart1_Click(object sender, EventArgs e)
{
}
private void OnTimedEvent(Object source, ElapsedEventArgs e)
{
drawChart();
}
}
}
Thanks in advance for your help.
While its not the best way to do it, for a beginner the easist way to avoid the problem is to use the following variable form.CheckForIllegalCrossThreadCalls = false;
Related
private void Form1_KeyPress(object sender, KeyPressEventArgs e)
{
if (this.m_keyCode == Keys.Enter)
{
webBrowser1.Navigate(textBox1.Text);
}
public static bool WriteBeamDataToFile(string Filename, List<Part> Parts)
{
// Open a Streamwriter to write data to the specified Filename
using (StreamWriter TeklaDataWriter = new StreamWriter(Filename))
{
// Connect to the Currently Open Tekla Model
Model Model = new Model();
foreach (Part CurrentPart in Parts)
{
if (CurrentPart != null)
{
string Name = CurrentPart.Name;
string Profile = CurrentPart.Profile.ProfileString;
string Material = CurrentPart.Material.MaterialString;
string Finish = CurrentPart.Finish;
TeklaDataWriter.WriteLine(Name + "," + Profile + "," + Material + "," + Finish);
}
}
}
return File.Exists(Filename);
}
Example:
private void button1_Click(object sender, EventArgs e)
{
How to call above method here?
}
private void button1_Click(object sender, EventArgs e) {
private bool isFileExists;
List<Parts> partsList = new List<Parts>();
isFileExists = WriteBeamDataToFile("example.txt",partsList)
if(isFileExists){
//do something..
}
}
Method above is mark as static. That's why you faced some issue.
Static method could be call from Class it' self.
While non static methods could be called from class instance.
See example:
class MyClass {
//static method
public static void Method1() {}
//non static method
public void Method2() {}
}
class MyForm:Form {
...
private void button1_Click(object sender, EventArgs e)
{
//here we call static method of MyClass
MyClass.Method1();
}
//or
private void button1_Click(object sender, EventArgs e)
{
// Here we create an instance of MyClass
var class = new MyClass();
// and call non static Method
class.Method2();
}
}
}
using System.Data.OleDb;
namespace ConnectingToMS_Access1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
OleDbDataAdapter da;
DataSet ds;
private void Form1_Load(object sender, EventArgs e)
{
da = new OleDbDataAdapter("Select * from Record", "Provider=Microsoft.Ace.oledb.12.0;data source='D:\\mydb.accdb'");
ds = new DataSet();
da.Fill(ds);
}
private void button1_Click(object sender, EventArgs e)
{
dataGridView1.DataSource = ds.Tables[0];
}
private void button2_Click(object sender, EventArgs e)
{
DataRow dr = ds.Tables[0].NewRow();
dr[0] = "abc";
dr[1] = "def";
dr[2] = "ghi";
dr[3] = "jkl";
ds.Tables[0].Rows.Add(dr);
}
private void button3_Click(object sender, EventArgs e)
{
OleDbCommandBuilder cb = new OleDbCommandBuilder(da);
da.Update(ds.Tables[0]);
MessageBox.Show("Saved in Database");
}
}
}
You need to explicitly define the named columns in your query.
The problem is that you can't update columns based on column position. It might have been reasonable to expect that calling the Fill method would return both records and column-names, but it probably won't. After all, running that select query will return only data, not schema.
public event EventHandler MyButtonClick = delegate { };
The construction above allows to not check if there is any subscriber:
public virtual void OnMyButtonClick(EventHandler e)
{
this.MyButtonClick(this, e);
}
in stead of
public virtual void OnMyButtonClick(EventHandler e)
{
if (MyButtonClick!=null)
this.MyButtonClick(this, e);
}
But is it really a good idea? Is this the only benefit: to not check if any subscriber exists?
UPDATE: Here is example
namespace ConsoleApplication2
{
public class TestClass
{
public event EventHandler MyButtonClick;
//= delegate { };
public void OnButtonClick(EventArgs e)
{
MyButtonClick(this, e);
}
}
class Program
{
static void Main(string[] args)
{
var testClass = new TestClass();
//it throws an exception
testClass.OnButtonClick(new EventArgs());
// if you add an handler it will call it
testClass.MyButtonClick += myCustomHandler;
testClass.OnButtonClick(new EventArgs()); // myCustomHandler has been invoiked
}
private static void myCustomHandler(object sender, EventArgs e)
{
Console.WriteLine("myCustomHandler has been invoiked");
}
}
}
Well, the code you've given here:
public virtual void OnMyButtonClick(EventHandler e)
{
if (MyButtonClick!=null)
this.MyButtonClick(this, e);
}
isn't thread-safe. If the final subscription is removed after the nullity check but before the invocation, you could end up with a NullReferenceException (depending on whether the "raising" thread sees the change).
So you can change it to this instead:
public virtual void OnMyButtonClick(EventArgs e)
{
var handler = MyButtonClick;
if (handler != null)
{
handler(this, e);
}
}
... but of course you might forget to do that, and even if you don't, it's cumbersome to do that all over the place, IMO. So yes, while the benefit is "only" to avoid the nullity check, I'd say that's not a bad trade-off in many cases. Anything that makes it harder to make mistakes is a good idea, IMO.
Another alternative is to have an extension method:
public static void SafeInvoke(this EventHandler handler, object sender,
EventArgs e)
{
if (handler != null)
{
handler(sender, e);
}
}
Then change your calling code to:
public virtual void OnMyButtonClick(EventArgs e)
{
MyButtonClick.SafeInvoke(this, e);
}
(and use the same code for other events). You'd probably want a generic form for EventHandler<T> as well.
you don't need to do that. If the client that uses you class won't add an handler (subscriber) for MyButtonClick event the code won't throw an exception.
That is how events works (and delegates as there are the same thing) otherwise you would be forced to add an handler to all the events of a class (assuming there are any)
so you can do the below:
public virtual void OnMyButtonClick(EventArgs e)
{
MyButtonClick(this, e);
}
have a look at the example below:
public class TestClass
{
public event EventHandler MyButtonClick = delegate { };
public void ButtonClick(EventArgs e)
{
MyButtonClick(this,e);
}
}
class Program
{
static void Main(string[] args)
{
var testClass=new TestClass();
testClass.ButtonClick(new EventArgs());
// if you add an handler it will call it
testClass.MyButtonClick += myCustomHandler;
testClass.ButtonClick(new EventArgs()); // myCustomHandler has been invoiked
}
private static void myCustomHandler(object sender, EventArgs e)
{
Console.WriteLine("myCustomHandler has been invoiked");
}
}
[DefaultEvent("MyCustomEvent")]
public partial class WebUserControl1 : System.Web.UI.UserControl
{
public delegate void onButtonClick(object sender, Myeventargs e);
public event onButtonClick btnHandler;
protected void ASPxButton1_Click(object sender, EventArgs e)
{
if (btnHandler != null)
{
btnHandler(this,e);
}
}
}
this code can work with
public partial class jscript : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
XFButton1.MYClick += new EventHandler(XFButton1_MYClick);
}
void XFButton1_MYClick(object sender, EventArgs e)
{
ASPxLabel1.Text = "Hello";
}
but the problem is i want it automatically generate a new event when i double click on the button. can i done this by using a web user control ?
too bad to tell you that web user control may not able to do like that... pls read this http://dotnet-framework-aspnet.itgroups.info/32/9/thread-796040.html.