Select All Checkbox and CheckedListBox

Question

I have a form that contains two elements: a CheckedListBox and a CheckBox. The CheckBox, which is called SelectAllCheckBox, is used to check/uncheck all items in the CheckedListBox. I achieve this via a CheckedChanged event handler associated with the SelectAllCheckBox, so that when it is checked, all items in the CheckedListBox are checked, and vice versa. This works fine.

I also have code that unchecks the SelectAllCheckBox when the user unchecks one of the CheckBoxes in the CheckedListBox. For example, if the user checks the SelectAllCheckBox, and then unchecks one of the items, the Select All CheckBox should be unchecked. This is achieved via the CheckedListBox.ItemChecked event handler. This also works fine.

My problem is that when the SelectAllCheckBox is programatically unchecked (as in the above scenario), its event handler causes all items in the CheckedListBox to become unchecked.

I'm sure others have run into my issue; is there an elegant workaround?

Answer 1

Another way is to utilize the fact that when you programmatically check/uncheck, it does not give focus to the checkbox. So you can use the Focused property as a flag.

private void SelectAllCheckBox_CheckedChanged(object sender, EventArgs e)
{
    if(!((CheckBox)sender).Focused) 
       return;
    //your code to uncheck/check all CheckedListBox here
}

No need to create another separate bool flag (unless if you are manually changing the focus state somewhere).

Answer 2

You can use some flag:

 bool suppressCheckedChanged;
 private void SelectAllCheckBox_CheckedChanged(object sender, EventArgs e){
    if(suppressCheckedChanged) return;
    //your code here
    //....
 }
 //Then whenever you want to programmatically change the Checked of your SelectAllCheckBox
 //you can do something like this
 suppressCheckedChanged = true;
 SelectAllCheckBox.Checked = false;
 suppressCheckedChanged = false;

Another approach is you can try another kind of event such as Click and DoubleClick (must use both):

private void SelectAllCheckBox_Click(object sender, EventArgs e){
   DoStuff();
}
private void SelectAllCheckBox_DoubleClick(object sender, EventArgs e){
   DoStuff();
}
private void DoStuff(){
   //your code here;
   if(SelectAllCheckBox.Checked){
      //....
   }
   else {
     //....
   }
}