Event unsubscription in another file

naura pax

hi,
I am working in a window project, which has a reference of a utility project that contains generic methods. for example one for binding combobox with dataset at runtime-:

 

ComboUtils.FillComboBox(cmbSubRegister, 
RGMaster.GetRegisterByParentID(Convert.ToInt32(cmbRegister.SelectedValue), false), 
true, "RegisterName", "RegisterID");

The ComboUtils.Fillcombobox function has follwoing definition

 

public static void 
FillComboBox(ComboBox cmb, object obj, 
bool valFieldRequired, string dispField, string valField) { 

if (obj.GetType().ToString() == "System.Data.DataSet")

{ 

cmb.DisplayMember = dispField;

if (valFieldRequired)

cmb.ValueMember = valField; 

cmb.DataSource = ((DataSet)obj).Tables[0];

}

Now the problem is that selectedindex changed event gets fired.
I tried to unsubscribe selectedindexchanged event from combobox object being passed and later resusbscribe after datasource has been set but i just can't get reference of the event handler in this file.
-: EventHandler ev=cmb.SelectedIndexChanged gives error that it can only be at the left hand side of += operator.
Can somebody tell me how to do that?
Please.. thanks in advance.

13 Replies

Know the answer? Post it — somebody with the same question will find it here.

Nilanka Dharmadasa17y ago
Hi maggog,
You can do it using method overloading, without changing the method signature.
Deepak Bhatia17y ago
Hi there, If you want to unsuscribe any event in C# the following code will help ypu to undesrtand ............ ............ ............ ............ EVENT SelectedIndexChanged of combo box IS Registered with function comboBoxCheckingEvents_SelectedIndexChanged ............ ............ ............ private void comboBoxCheckingEvents_SelectedIndexChanged(object sender, EventArgs e) { textBoxCmbValue.AppendText(comboBoxCheckingEvents.Text); } ............ ............ ............ Now I have made a button to unsucribe the events ............ ............ ............ private void buttonRemoveComboEvent_Click(object sender, EventArgs e) { comboBoxCheckingEvents.SelectedIndexChanged -= comboBoxCheckingEvents_SelectedIndexChanged; } ............ ............ ............ ............ ............ ............ Afte clicking the button remove selected index changed get unregistered.
jinge17y ago
Again. event-= eventHandler does not work?
naura pax17y ago
hi niki,
sorry i lost net connection.
Talking about your suggestion, I hope you tested that well, i had that thing in mind but the main problem is there are two many comboboxes accross two many forms many of which are not under my control that are using method.
if i change signature of the function the client code will break and everychange will have to be made that's why i was looking for a workaround.
Thanks anyways.
bebo
Nilanka Dharmadasa17y ago
Hey Maggogg,

Why are you silent? What happened?
jinge17y ago
Hi guy,

I am confused, what did you want exactly? why does the above piece code not work for you. Hope you can elaborate it more.

Nilanka Dharmadasa17y ago

Hi friend,
Sorry. Now only I got ur problem. I think this solution should work.

 

public static void FillComboBox(ComboBox cmb, object obj, bool 
valFieldRequired, string dispField, string valField, System.EventHandler g)
{  

if (obj.GetType().ToString() == "System.Data.DataSet")
{ 

cmb.DisplayMember = 
dispField;
if (valFieldRequired) 
cmb.ValueMember = valField;
cmb.SelectedIndexChanged -= g;
cmb.DataSource = ((DataSet)obj).Tables[0];
cmb.SelectedIndexChanged += g;


}


}

When you pass values for the method you should pass like ths.

 

ComboUtils.FillComboBox(cmbSubRegister, 
RGMaster.GetRegisterByParentID(Convert.ToInt32(cmbRegister.SelectedValue), false), 
true, "RegisterName", "RegisterID", this.cmb_SelectedIndexChanged

);

If this helps you, please accept my answer.

naura pax17y ago
boy thats what i'm saying create a function in another class in another file
pass your combobox , dataset, displaymember, valuemember
and try & do this in that function
event-= eventhandler; dojob(); event+=eventhandler;
jinge17y ago
Did you try
event-= eventhandler; dojob(); event+=eventhandler;
Does it work?
naura pax17y ago
hey jinge bro,
there is no error i have reference for window project and all that.
point is at the time of setting datasource of combobox selectedindexchanged event gets fired, but that function is being run in another file where i can't get reference of event handler.
I want to remove event handler and reassign it to avoid selectedindexchanged from getting fired.
hope you got it.
jinge17y ago
Hi friend,

Let me explain why the error happens. First we all know that ComboBox has SelectedIndexChanged event, but why Visual Studio complies with error?

I think that's because in your utility project, you does not add reference to Windows.Forms.Controls assembly which is not added automatically when it is a libray project.
naura pax17y ago
hey niki,
selectedindexchanged event still gets fired.
can you explain what you are trying to do here? I didn't get it.. please.

Nilanka Dharmadasa17y ago

Try this.

 

public static void FillComboBox(ComboBox cmb, object obj, bool valFieldRequired, string dispField, string valField)
 {  
if (obj.GetType().ToString() == "System.Data.DataSet")
 { 
cmb.BeginUpdate();
cmb.DisplayMember = dispField;
if (valFieldRequired) 
cmb.ValueMember = valField;
cmb.DataSource = ((DataSet)obj).Tables[0];
cmb.EndUpdate();

 }

}

If my answer helps you, pls accept it.