Develop Reference

C# pass delegates to different forms

i have a WinForms app that consists of several forms.
What I'm trying to achieve is to pass an event handler from a second form, to a third one, but i cannot achieve that. i get a casting error which i can't figure out how to overcome.
i would appreciate the help:
code + further explanation below:
This is a rough image of what is supposed to happen:
Form1 can create several forms (it also holds the methods that i want to pass) - which i can pass successfully on sub form creation.
the problem starts when i create form3 from within form2: i try to pass the event handler, but i get Error CS0029/CS0030 (casting errors)
what am i doing wrong and how to fix it?
EDIT:
what needs to happen? -- Form3 needs to control (send back data) to a Gui control placed in Form1
Code:
Form1:
public delegate void sendMessageToConsoleDelegate(string value);
public sendMessageToConsoleDelegate sendMessageToConsoleCallback;
public delegate void SetPlaceHolderDelegate(TextBox tb);
public SetPlaceHolderDelegate SetPlaceHolderCallback;
private void SetPlaceHolder(TextBox tb)
{
if (!tb.InvokeRequired)
{
if (!tb.Focused)
{
if (string.IsNullOrWhiteSpace(tb.Text))
tb.Text = tb.Tag.ToString();
return;
}
if (tb.Text == tb.Tag.ToString())
tb.Text = "";
return;
}
SetPlaceHolderDelegate call = new SetPlaceHolderDelegate(SetPlaceHolder);
tb.BeginInvoke(call, tb);
}
private void SendMessageToConsole(string msg)
{
if (!textBoxConsole.InvokeRequired)
{
textBoxConsole.AppendText(msg);
return;
}
sendMessageToConsoleDelegate call = new sendMessageToConsoleDelegate(SendMessageToConsole);
textBoxConsole.BeginInvoke(call, msg);
}
private void AddNewDeviceForm()
{
frmAddDevice add_device = new frmAddDevice(devicesDBPath);
add_device.sendMessageToConsole += SendMessageToConsole;
add_device.Show();
}
private void StartEdit()
{
frmEditDBs editdb = new frmEditDBs(devicesDBPath, commandsDBPath);
editdb.sendMessageToConsole += SendMessageToConsole;
editdb.SetPlaceHolder += SetPlaceHolder;
editdb.Show();
}
Form2 (frmEditDBs)
public delegate void EventHandler_sendMessageToConsole(string msg);
public event EventHandler_sendMessageToConsole sendMessageToConsole = delegate { };
public delegate void EventHandler_SetPlaceHolder(TextBox tb);
public event EventHandler_SetPlaceHolder SetPlaceHolder = delegate { };
private void EditDevice()
{
frmAddDevice edit_device = new frmAddDevice(devicesDBpath, current_device);
edit_device.sendMessageToConsole += sendMessageToConsole; ****<== This is the issue (same for the placeholder)****
edit_device.Show();
}
i get error CS0029
how can i pass the same delegate to other sub forms (e.g. frmAddDevice)?

Your question is how to C# pass delegates to different forms so that you can (for example) sendMessageToConsole to your MainForm from the other forms. In your code you state that this is the problem:
// This is the issue (same for the placeholder)****
edit_device.sendMessageToConsole += sendMessageToConsole;
When I look at your code, in essence you are trying to implement your own version of an Event Pattern. One solution to your issue would be to use a standard event pattern. Then intellisense will recognize your custom event delegate in the standard way:
FIRST you need to make the delegate and the inherited EventArgs class outside of your MainForm class:
namespace pass_delegates
{
public partial class MainForm : Form
{
}
// Make sure these are outside of any other class.
public delegate void SendMessageToConsoleEventHandler(object sender, SendMessageToConsoleEventArgs e);
public class SendMessageToConsoleEventArgs : EventArgs
{
public string Message { get; }
public SendMessageToConsoleEventArgs(string message)
{
Message = message;
}
}
}
Your frmAddDevice (shown here in minimal format) declares the delegate using the event keyword. Your other form frmEditDBs does exactly the same thing.
public partial class frmAddDevice : Form
{
public event SendMessageToConsoleEventHandler SendMessageToConsole;
public frmAddDevice(string devicesDBpath)
{
InitializeComponent();
}
protected virtual void OnSendMessageToConsole(SendMessageToConsoleEventArgs e)
{
SendMessageToConsole?.Invoke(this, e);
}
// Clicking the button will call this as a test.
private void btnSendTestMessage_Click(object sender, EventArgs e)
{
OnSendMessageToConsole(new SendMessageToConsoleEventArgs("Message received from 'Add Device Form'"));
}
}
A button in the MainForm code creates a new frmAddDevice like this:
frmAddDevice frmAddDevice = null;
// This handler in the Main Form creates the frmAddDevice form
private void btnFrmAddDevice_Click(object sender, EventArgs e)
{
if (frmAddDevice == null)
{
frmAddDevice = new frmAddDevice(devicesDBpath: "Some path");
// This was the problem. Not anymore ****
frmAddDevice.SendMessageToConsole += outputMessageToConsole;
}
frmAddDevice.Show();
}
private void outputMessageToConsole(object sender, SendMessageToConsoleEventArgs e)
{
textBoxConsole.AppendText(e.Message + Environment.NewLine);
}
If you do these things, you will achieve the functionality of sendMessageToConsole that your code is attempting to do. Try it out by downloading my sample from GitHub.

I think the main concept you don't understand is that delegate is "same level" as class, enum, struct etc. You need to declare it in some shared scope to make it accessible in both forms.
namespace ConsoleApp6
{
public delegate void TestDelegate();
public class ClassA
{
public TestDelegate delegateA;
}
public class ClassB
{
public TestDelegate delegateB;
}
internal class Program
{
static void Main(string[] args)
{
TestDelegate del = () => { };
var classA = new ClassA()
{
delegateA = del,
};
var classB = new ClassB()
{
delegateB = classA.delegateA
};
}
}
}
Or, if you want to keep it inside of the form, you need reference it by a class name the same way you would do with a type.
namespace ConsoleApp6
{
public class ClassA
{
public delegate void TestDelegate();
public TestDelegate delegateA;
}
public class ClassB
{
public ClassA.TestDelegate delegateB;
}
internal class Program
{
static void Main(string[] args)
{
ClassA.TestDelegate del = () => { };
var classA = new ClassA()
{
delegateA = del,
};
var classB = new ClassB()
{
delegateB = classA.delegateA
};
}
}
}

As was described previously, your "delegates" should be declared generically at the namespace of your project, not within a specific class so they are visible throughout your app. To do so, maybe make a separate file in your project for "MyDelegates" and may look something like:
using System.Windows.Forms;
namespace WinHelp1
{
// Create your own delegates outside of your classes that need to be publicly
// visible within your app or even protected if so needed.
public delegate void EventHandler_SendMessageToConsole(string msg);
public delegate void EventHandler_SetPlaceHolder(TextBox tb);
}
Now, in your form 1 that you want to define WHAT to do, do so based on the signatures matching appropriately
using System.Windows.Forms;
namespace WinHelp1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
public void DoThisForConsole(string msg)
{
// whatever to do with string
}
public void DoThisForTextBox(TextBox tb)
{
// whatever to do with textbox
}
private void Btn2_Click(object sender, System.EventArgs e)
{
var f2 = new Form2();
f2.SendMessageToConsole += DoThisForConsole;
f2.SetPlaceHolder += DoThisForTextBox;
f2.ShowDialog();
// OR, if using the PARAMETERIZED for pass-through to call
// when form2 calls form 3
var f2b = new Form2( DoThisForConsole, DoThisForTextBox );
f2b.ShowDialog();
}
private void Btn3_Click(object sender, System.EventArgs e)
{
var f3 = new Form3();
f3.SendMessageToConsole += DoThisForConsole;
f3.SetPlaceHolder += DoThisForTextBox;
f3.ShowDialog();
}
}
}
First, form3 since that will just have the direct event handlers, and you can invoke however within form 3
using System.Windows.Forms;
namespace WinHelp1
{
public partial class Form3 : Form
{
// now, for each form you want to USE them on...
public event EventHandler_SendMessageToConsole SendMessageToConsole;
public event EventHandler_SetPlaceHolder SetPlaceHolder;
public Form3()
{
InitializeComponent();
}
}
}
Now, in your form 2, is a bit different. Since you want to make available for form2 to call form3 with the same event handler, just add those event handlers as parameters to the constructor class. Then you can preserve them in that form, but at the same time, self-register them as in the var f2b = new Form2 of the second button click event. Then use those preserved values when form2 needs to call form3
using System.Windows.Forms;
namespace WinHelp1
{
public partial class Form2 : Form
{
// now, for each form you want to USE them on...
public event EventHandler_SendMessageToConsole SendMessageToConsole;
public event EventHandler_SetPlaceHolder SetPlaceHolder;
// now, for each form you want to USE them on...
public EventHandler_SendMessageToConsole passThroughForMessage;
public EventHandler_SetPlaceHolder passThroughForTextBox;
public Form2()
{
InitializeComponent();
}
public Form2(EventHandler_SendMessageToConsole forSendMsg, EventHandler_SetPlaceHolder forPlaceHolder ) : this()
{
// preserve into properties in-case you need to call form 3
passThroughForMessage = forSendMsg;
passThroughForTextBox = forPlaceHolder;
// and the constructor can auto-set for itself so IT can notify as well
if( forSendMsg != null )
SendMessageToConsole += forSendMsg;
if( forPlaceHolder != null )
SetPlaceHolder += forPlaceHolder;
}
private void Btn3_Click(object sender, System.EventArgs e)
{
var f3 = new Form3();
// and the constructor can auto-set for itself so IT can notify as well
if (passThroughForMessage != null)
f3.SendMessageToConsole += passThroughForMessage;
if (passThroughForTextBox != null)
f3.SetPlaceHolder += passThroughForTextBox;
f3.ShowDialog();
}
}
}
Remember, parameters can be practically anything, and you can have a variable stored in a property just like anything else... as long as it matches the respective type.
Then, from form3, either instance will invoke back to whatever the root instance method may be.

Repopulate a form field from a different class in C#

I'm trying to repopulate a textbox from a separate class. I've looked through a number of instances of this same question and found what I thought was a good solution. But, I can't make it work. I've tried to resolve the issue by creating a separate thread to send the data back. I don't know if this is a great idea or not. But, I know the data is getting back to the correct place without it because it shows up in the console. Any suggestions? Thanks!
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
public void updater(double value)
{
textBox1.Text = value.ToString(); // Trying to update here
Console.WriteLine(value); // The new multiple makes if back to here...
}
private void button1_Click(object sender, EventArgs e)
{
CALC c = new CALC();
c.valuecalculator(.0025);
}
}
public class CALC
{
public void valuecalculator(double multiplier)
{
for (int index = 0; index < 1000; index++)
{
Form1 f = new Form1();
double newMultiple = index * multiplier;
f.updater(newMultiple);
}
}
}

You're making a new copy of the form in your valuecalculator method, but you should be using the same form.
There are loads of ways to solve this.
You could pass an instance of the form into your valuecalculator method.
You could make the reference to the form static in your Program.cs or whatever startup file originally initialises it.
You could give the form a reference to itself
You could put the code to update the form in the button1 click event (this makes most sense) by making the valuecalculator return the result instead of returning void

Your components should only do one thing. The calculator should perform a calculation and return the result:
public static class Calc
{
public static double CalculateValue(double multiplier)
{
return 100 * multiplier;
}
}
Forms should be as simple as possible. Meaning they are only concerned with displaying form elements and passing events to event handlers. The actual logic that happens in these event handlers should be someone else's responsibility. I like to pass this logic in the constructor:
public partial class Form1 : Form
{
public Form1(Func<double, double>CalculateValue)
{
InitializeComponent();
button1.Click += (sender, eventArgs) => textBox1.Text = CalculateValue(.0025).ToString();
}
}
Constructing and connecting classes with each other is another responsibility. The simplest version is to use your Main() method:
static class Program
{
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
var form = new Form1(Calc.CalculateValue);
Application.Run(form);
}
}

passing value from another class to textbox in form?

I have a class and a form. the class is intended to do some processes when event is raised and return back the values to the form to display only. I kind of have problem passing values back to form. For instance, I have this code in class print:
public class PrintClass : Form1
{
public void printEventHandler(object sender, EventArgs e)
{
string text = "Process Completed";
append_Tbox(text);
}
}
and the method in form1 to display the text:
public void append_Tbox(string s)
{
TboxPrint.AppendText(s);
}
However, nothing is displayed. I believe there is something wrong, but I can't figure it out.
What is the fastest way to pass values from the class to form?

First off, your processing class shouldn't extend Form1. This is giving you the illusion that you can access the methods of your existing form, but it's not doing what you think it is. You're creating an entirely new form when you do this, and just not showing it. That form has it's own set of all instance fields, so you're not accessing the controls of your main form. Even if this would work (and it won't) it's not a well designed solution.
The proper way to do this is actually much easier. You just need to have your other class return a value from it's method:
public class PrintClass
{
public string DoWork()
{
Thread.Sleep(2000);//placeholder for real work.
return "Process Completed";
}
}
Now your main form can just call that method and append the return value to a textbox.
Once you do this you'll have an entirely separate issue. If you do the work in the UI thread you'll be blocking that UI thread while the work takes place, preventing the form from being repainted, or any other events from being handled. You need to do the work in a background thread and then marshal back to the UI thread to update the UI with the results. There are a number of ways of doing this, but if you have C# 5.0 using await is by far the easiest:
public class Form1 : Form
{
private void SomeEventHandler(object sender, EventArgs args)
{
string result = await Task.Run(()=>new PrintClass().DoWork());
TboxPrint.AppendText(result);
}
}
If you need a C# 4.0 solution you can use ContinueWith, which is more or less what the above will be translated to, but it's not quite as clean of syntax.
public class Form1 : Form
{
private void SomeEventHandler(object sender, EventArgs args)
{
Task.Factory.StartNew(()=>new PrintClass().DoWork())
.ContinueWith(t => TboxPrint.AppendText(t.Result)
, CancellationToken.None
, TaskContinuationOptions.None
, TaskScheduler.FromCurrentSynchronizationContext());
}
}

I have create delegate in Main Form
public delegate void LoginDelegate(string s);
public partial class AirLineReservationMDI : Form
{
LoginDelegate loginAirLineDelegate;
}
loginAirLineDelegate = new LoginDelegate(DisableToolStripMenuItems);
public void DisableToolStripMenuItems(string s)
{
this.viewToolStripMenuItem.Visible = true;
this.bookingToolStripMenuItem.Visible = true;
this.existingUserToolStripMenuItem.Visible = false;
this.newUserToolStripMenuItem.Visible = false;
this.toolStripStatusUserID.Text = "USerID :- "+s;
this.LoginUserId = s;
}
in Another Class, (I have passed delagete object to this class )
I fired the Delegate
logDelegate(textBoxUserName.Text);

I used Action<T> delegate to solve the problem. here is the code and it works fine.
class PrintClass
{
public Action<string> DisplayDelegate;
public void printEventHandler(object sender, EventArgs e)
{
string text = "Event Handled, and text value is passed";
var copy = DisplayDelegate;
if (copy != null)
{
copy(text);
}
}
}
and in `Form1.cs' :
private void Form1_Load(object sender, EventArgs e)
{
PrintClass p = new PrintClass();
BtnPrint.Click += p.printEventHandler;
//subscrite the displayevent method to action delegate
p.DisplayDelegate += DisplayEvent;
}
public void DisplayEvent(string s)
{
Invoke(new Action(() => TboxPrint.AppendText(s)));
}
so the text 'Event Handled, and text value is passed' is displayed on the textbox.
I m not sure if it is the efficient way.
Thanks guys.

Unable to SET value from another class

Im trying to set LabelStatus's text to a message in the class but it doesn't work.
Here's my code:
Class:
public bool openConnection()
{
SetStatus("Connecting to " + Server);
//Mysql code
}
private void SetStatus(string msg)
{
Form1 form = new Form1();
form.SetStatus(msg);
}
Form1:
public void SetStatus(string status)
{
labelStatus.Text = _status;
}
I'm fairly new to C# (php guy) and for the life of me can't figure out what I am doing wrong

Try calling the ShowDialog or Show Method on your form
private void SetStatus(string msg)
{
Form1 form = new Form1();
form.SetStatus(msg);
form.ShowDialog(this);
}

looks like you are setting the member variable and not the function's parameter.
//try something like this
this._status = status;
this.labelStatus.Text = this._status;

When setting labelStatus.Text, you're not setting it with the parameter you passed to SetStatus(string). It seems like you accidentally used a data member instead.

Look at the names : try to make them same, see
labelStatus.Text = **status**;

From your code, I think your class is change the status label of form label. To change form label text you need object of already opened form. define variable for form in your class.
public class ConnectionCheck
{
private Form myForm;
public void ConnectionCheck(Form form)
{
myForm = form;
}
public bool openConnection()
{
SetStatus("Connecting to " + Server);
//Mysql code
}
private void SetStatus(string msg)
{
//Call method to change label text
myForm .SetStatus(msg);
}
}
Pass form1 object at the time of ConnectionCheck object creation from from1 codebehind(form1.cs).
ConnectionCheck connection = new ConnectionCheck(this);
And Also, change _status to parameter variable.
public void SetStatus(string status)
{
labelStatus.Text = status;
}

C# Set Form Parent after calling method from another class

I've searched Google all day and can't find the correct answer to my issue, hoping someone here can help me.
So, in the "Main" form I have the method to show a form that needs to be centered directly above the parent form (frmMain). Normally I would call ShowDialog(this) to see the parent, but for some reason I have to set the loadNewsFeedItem to static in order to see the method from the flpNewsFeedHeader : Label derrived class (below). The OnClick event triggers the method loadNewsFeedItem().
When I call this to set the parent, I'm getting the message "Keyword 'this' is not valid in a static property, static method, or static field initializer"
namespace NewsFeeds
{
public partial class FrmMain : Form
{
public static void loadNewsFeedItem()
{
frmNewsFeedView frmFeedView = new frmNewsFeedView(FrmFuncs.selFeedID);
frmFeedView.ShowDialog(this); // Error occurs on this line, when calling this via a static method
}
}
}
public class flpNewsFeedHeader : Label
{
private int FeedID = 0;
public int theFeedID
{
get { return FeedID; }
set { FeedID = value; }
}
protected override void OnClick(EventArgs e)
{
FrmFuncs.selFeedID = FeedID;
Thread thrShowFeed = new Thread(new ThreadStart(FrmMain.loadNewsFeedItem));
thrShowFeed.Start();
}
}
Can someone please give me a corrected code example or a hint as to how to get the loadNewsFeedItem() to be visible without setting the accessor to static, or how to work around this in a static accessor?
Thanks in advance!
Chris

Edit: used ActiveForm for owner.
public partial class FrmMain : Form
{
public static void loadNewsFeedItem(Form owner)
{
frmNewsFeedView frmFeedView = new frmNewsFeedView(FrmFuncs.selFeedID);
frmFeedView.ShowDialog(owner);
}
}
}
public class flpNewsFeedHeader : Label
{
private int FeedID = 0;
public int theFeedID
{
get { return FeedID; }
set { FeedID = value; }
}
protected override void OnClick(EventArgs e)
{
FrmFuncs.selFeedID = FeedID;
// Shouldn't need a new thread. Already on the GUI thread.
FrmMain.loadNewsFeedItem (System.Windows.Forms.Form.ActiveForm);
}
}

may be you mean this:
frmFeedView.Owner = System.Windows.Forms.Form.ActiveForm;
frmFeedView.ShowDialog();

In a static method, this is meaningless. One option is to skip the parameter
frmFeedView.ShowDialog();
The other option is to setup a static variable as shown below (but beware, it can have side effects if you try to open multiple instances of FrmMain)
public partial class FrmMain : Form
{
private static FrmMain staticInstance;
public FrmMain()
{
staticInstance = this;
InitializeComponent();
...
}
public static void loadNewsFeedItem()
{
frmNewsFeedView frmFeedView = new frmNewsFeedView(FrmFuncs.selFeedID);
frmFeedView.ShowDialog(staticInstance );
}