Why loaded event of combobox do not save the list?

Question

I have class say class A and i have cintialised a list (I am using HashSet) in the costructor so as to have its access throught out the program.

I Add the item in the list inside the Loaded event of comboBox. Ans i use that saved list after the loaded event I found that it do not contain the data i added.

Is this thing normal with loaded event ? Could some one please tell me way to save data added inside the List (I am using HashSet) in loaded event? My code is :

 static HashSet < string > listOfUpdatedUIElement = new HashSet < string > ();
 static HashSet < string > storeUpdatedUIElement = new HashSet < string > ();
  //This in constructor
 GenerateParametersPreview() 
 {
     storeUpdatedUIElement = null;
 }


 public Grid simeFunction() {
     ComboBox cmb = new ComboBox();
     cmb.Loaded += (o3, e) => {
         foreach(string atrb in listOfUpdatedUIElement) //I have seen on debugging the data are updated in listOfUpdatedUIElement 
             {
                 storeUpdatedUIElement.Add(atrb);
             }
     };

     foreach(string atrb in storeUpdatedUIElement) //Here storeUpdatedUIElement hashset contains nothing inside
         {
             cmb.Items.Add(atrb);
         }
     Grid.SetColumn(cmb, 1);
     comboRowGrid.Children.Add(cmb);
     Grid.SetRow(comboRowGrid, 0);
     bigGrid.Children.Add(comboRowGrid); //suppose ihad created this bigGrid and it will dispaly my comboBox
     return (bigGrid);
 }

score 1 · Answer 1 · answered Aug 07 '14 at 12:14

1

simeFunction is working using a new new combobox that is never added to your form.

You are expecting your list to be populated when this combobox is loaded and since it is never added to your form, it never will be loaded.

answered Aug 07 '14 at 12:14

Sayse

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Are you talking about "Grid.SetColumn(cmb, 1); comboRowGrid.Children.Add(cmb);" please see the edit. It still donot work (but that was understood) – user3735822 Aug 07 '14 at 12:19
@user3735822 - `ComboBox cmb = new ComboBox();` You are working with a **new** combo box, its possible you are expecting this to be an existing combobox already on your form. But then I can't see the importance of loading the combobox – Sayse Aug 07 '14 at 12:22
1

@user3735822 - After looking again, yes this is the correct part of code, but since you won't have loaded it until after it has been added, your foreach loop will have already gone past the empty list – Sayse Aug 07 '14 at 12:24

score 1 · Accepted Answer · answered Aug 07 '14 at 12:21

The events are the main tool of the Event-driven-programming paradigm.

In event driven programming you are not sure when and whether at all some condition changes (like some ComboBox is finally loaded or not), you are reacting to the notification about that change - raised event.

It means that

cmb.Loaded += (o3, e) =>
       {
         foreach(string atrb in listOfUpdatedUIElement)//I have seen on debugging the data are updated in listOfUpdatedUIElement 
         {
             storeUpdatedUIElement.Add(atrb);
         }
     };

won't(at least it is hardly possible) execute before the

 foreach(string atrb in storeUpdatedUIElement) //Here storeUpdatedUIElement hashset contains nothing inside
 {
     cmb.Items.Add(atrb);
 }

That's why the storeUpdatedUIElement is empty when the loop enumerates it.

SOLUTION:

So, if you want to update your ComboBox items on Loaded event you should put all the relevant code inside the event:

cmb.Loaded += (o3, e) =>
{
     foreach(string atrb in listOfUpdatedUIElement)//I have seen on debugging the data are updated in listOfUpdatedUIElement 
     {
         storeUpdatedUIElement.Add(atrb);
     }

     foreach(string atrb in storeUpdatedUIElement) //Here storeUpdatedUIElement hashset contains nothing inside
     {
         cmb.Items.Add(atrb);
     }  
};

P.S.: In such a case you should probably unite those two loops in one:

     foreach(string atrb in listOfUpdatedUIElement)//I have seen on debugging the data are updated in listOfUpdatedUIElement 
     {             
         storeUpdatedUIElement.Add(atrb); // Remove it too if it is not used anywhere else
         cmb.Items.Add(atrb);
     }

Why loaded event of combobox do not save the list?

2 Answers2