[RESOLVED] Change form control properties in different class with method ?

[LuckyLuke82]

hi,

how could I write a method in class which I could then use for control events in all forms ? I have labels with same images and same Mouse_Enter, Mouse_Leave code and I want to write a method which I could simply subcribe to all labels in different forms.

[jmcilhinney]

E.g.

Module LabelEventHandlers
 
    Public Sub MouseEnterHandler(sender As Object, e As EventArgs)
        Dim lbl = DirectCast(sender, Label)
 
        '...
    End Sub
 
    Public Sub MouseLeaveHandler(sender As Object, e As EventArgs)
        Dim lbl = DirectCast(sender, Label)
 
        '...
    End Sub
 
End Module

Public Class Form1
 
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        AddHandler Label1.MouseEnter, AddressOf LabelEventHandlers.MouseEnterHandler
        AddHandler Label1.MouseLeave, AddressOf LabelEventHandlers.MouseLeaveHandler
    End Sub
 
    Private Sub Form1_FormClosed(sender As Object, e As FormClosedEventArgs) Handles Me.FormClosed
        RemoveHandler Label1.MouseEnter, AddressOf LabelEventHandlers.MouseEnterHandler
        RemoveHandler Label1.MouseLeave, AddressOf LabelEventHandlers.MouseLeaveHandler
    End Sub
 
End Class

[LuckyLuke82]

So there isn't any shorter way to do this ? I was hoping for something without AddHandler method in C#.

Is RemoveHandler allways neccesary, what can happen If not included in code ? And I've seen some C# code where they register event in constructor, right after Initialize component() - what's the difference from registering in Load ?

Beside that - is this a valid code in C# or should It be better to use something else when you need to reference form or other controls too from same method :

 
        public static void Enter(object sender, EventArgs e)
        {
            dynamic lbl = (Label)sender;

            Form frm = lbl.Parent;
            frm.Cursor=Cursors.Hand;

            frm.Controls["Textbox1"].Text = "Test";

            lbl.Image=Properties.Resources.Smile;
        }

        public static void Leave(object sender, EventArgs e)
        {
            dynamic lbl = (Label)sender;

            Form frm = lbl.Parent;
            frm.Cursor = Cursors.Default;
            frm.Controls["Textbox1"].Text = "";

            lbl.Image = Properties.Resources.Cry;
        }

[jmcilhinney]

Sorry, I answer most of my questions in the VB.NET forum and I must have forgotten that this one was in C# when I answered it. The C# code would be basically the same though.

static class LabelEventHandlers
{
    public static void MouseEnterHandler(object sender, EventArgs e)
    {
        var lbl = (Label)sender;
 
        // ...
    }
 
    public static void MouseLeaveHandler(object sender, EventArgs e)
    {
        var lbl = (Label)sender;
 
        // ...
    }
}

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }
 
    private void Form1_Load(object sender, EventArgs e)
    {
        label1.MouseEnter += LabelEventHandlers.MouseEnterHandler;
        label1.MouseLeave += LabelEventHandlers.MouseLeaveHandler;
    }
 
    private void Form1_FormClosed(object sender, FormClosedEventArgs e)
    {
        label1.MouseEnter -= LabelEventHandlers.MouseEnterHandler;
        label1.MouseLeave -= LabelEventHandlers.MouseLeaveHandler;
    }
}

So there isn't any shorter way to do this ? I was hoping for something without AddHandler method in C#.

C# uses the '+=' operator to do the same job as AddHandler but you need to use it in order to register an event handler. I'm not sure how much shorter you were hoping for but I don't really see that using AddHandler in VB is long. If what you actually mean is that you don't want to have to write a statement for each event of each control then an option might be to add a method to the same class as the event handling methods themselves are members of, so you can just call one method and pass in a control and it will register all the event handlers:

static class LabelEventHandlers
{
    public static void RegisterEventHandlers(Label lbl)
    {
        lbl.MouseEnter += MouseEnterHandler;
        lbl.MouseLeave += MouseLeaveHandler;
    }
 
    public static void UnregisterEventHandlers(Label lbl)
    {
        lbl.MouseEnter -= MouseEnterHandler;
        lbl.MouseLeave -= MouseLeaveHandler;
    }
 
    public static void MouseEnterHandler(object sender, EventArgs e)
    {
        var lbl = (Label)sender;
 
        // ...
    }
 
    public static void MouseLeaveHandler(object sender, EventArgs e)
    {
        var lbl = (Label)sender;
 
        // ...
    }
}

You still need one line per event but you only have to write those lines once, instead of once per control.

Is RemoveHandler allways neccesary, what can happen If not included in code ?

You generally should use RemoveHandler in VB and '-=' in C# whenever you use AddHandler and '+='. The reason is that the object whose event is being handled holds a reference to the object handling the event via the event handler delegate and that effects garbage collection. In this case though, if the class handling the events is static then there is no object to clean up while the app is running, so it might not be an issue. I would tend to do it anyway though, for consistency and the fact that there might be some other issue that I wasn't aware of.

And I've seen some C# code where they register event in constructor, right after Initialize component() - what's the difference from registering in Load ?

Certainly nothing wrong with doing it in the constructor. I rarely do things in a form constructor in VB unless I want to add parameters but, given that event handlers are registered in the constructor (or at least in the InitializeComponent method that is called from the constructor) when done in the designer, I can't really think of an argument against doing it. That applies even more in C#, where the constructor is in the user code file by default. If you are removing event handlers in the FormClosed event handler then adding them in the Load event handler offers some sort of symmetry, but that's a rather flimsy reason.

Beside that - is this a valid code in C# or should It be better to use something else when you need to reference form or other controls too from same method :

 
        public static void Enter(object sender, EventArgs e)
        {
            dynamic lbl = (Label)sender;

            Form frm = lbl.Parent;
            frm.Cursor=Cursors.Hand;

            frm.Controls["Textbox1"].Text = "Test";

            lbl.Image=Properties.Resources.Smile;
        }

        public static void Leave(object sender, EventArgs e)
        {
            dynamic lbl = (Label)sender;

            Form frm = lbl.Parent;
            frm.Cursor = Cursors.Default;
            frm.Controls["Textbox1"].Text = "";

            lbl.Image = Properties.Resources.Cry;
        }

I would say two things about that. Firstly, I would tend to call FindForm on the Label rather than using the Parent property. That allows for Labels that are added to child containers like Panels.

Secondly, don't reuse properties of Properties.Resources like that. Remember that resources are actually embedded in your EXE and every time you access a property like that, the embedded data is extracted and an object created. If you were to mouse over your Label 10 times, that code would create 20 Image objects and not dispose any of them. What you should do is access each property once and assign the result to a variable, then reuse that variable so that you are reusing the same object.

[LuckyLuke82]

You meant like this right ? :

registering events:

        private void Form2_Load(object sender, EventArgs e)
        {
            LabelEventHandlers.RegisterEventHandlers(label1);
        }

images:

    static Bitmap Cry = Properties.Resources.Cry;
      static Bitmap Smile = Properties.Resources.Smile;

        public static void Enter(object sender, EventArgs e)
        {
            dynamic lbl = (Label)sender;

            Form frm = lbl.FindForm();
            frm.Cursor = Cursors.Hand;

            frm.Controls["Textbox1"].Text = "Test";

            lbl.Image = Smile;
        }

        public static void Leave(object sender, EventArgs e)
        {
            dynamic lbl = (Label)sender;

            Form frm = lbl.FindForm();

            frm.Cursor = Cursors.Default;
            frm.Controls["Textbox1"].Text = "";

            lbl.Image = Cry;
        }

If that's the case then I'm satisfied, exactly something I was looking for. Thanks, again.

[jmcilhinney]

Yep, that's pretty much it. It feels a little dirty to me to be accessing a TextBox on the form like that but I guess I can live with it if it's internal.

[LuckyLuke82]

Yep, that's pretty much it. It feels a little dirty to me to be accessing a TextBox on the form like that but I guess I can live with it if it's internal.

Basically I don't need accessing other controls right now, but I included that in post to make sure If I can do It. What I need is reference to form only, to change cursor on label Mouse_Enter.

Thanks again!