What algorithm is used in this code?
This code checks and unchecks the child nodes of a treeview control. What algorithm is used in this code?
private int _callCountUp;
pr开发者_Python百科ivate int _callCountDn;
private void tvwPermissions_AfterCheck(object sender, System.Windows.Forms.TreeViewEventArgs e)
{
bool anyChecked = false;
if (_callCountDn == 0 && e.Node.Parent != null)
{
anyChecked = false;
foreach (TreeNode childNode in e.Node.Parent.Nodes)
{
if (childNode.Checked)
{
anyChecked = true;
break;
}
}
_callCountUp += 1;
if (anyChecked)
e.Node.Parent.Checked = true;
_callCountUp -= 1;
}
if (_callCountUp == 0)
{
foreach (TreeNode childNode in e.Node.Nodes)
{
_callCountDn += 1;
childNode.Checked = e.Node.Checked;
_callCountDn -= 1;
}
}
}
Not so sure this has a name. It is quite standard, the _callCountUp/Dn fields avoid trouble when changing the Checked property of a node causes the AfterCheck event handler to run again. StackOverflow is a very typical outcome when the event handler recurses without bound.
The generic pattern resembles this:
private bool modifyingNodes;
private void treeview_AfterCheck(object sender, TreeViewEventArgs e) {
if (modifyingNodes) return;
modifyingNodes = true;
try {
// etc..
}
finally {
modifyingNodes = false;
}
}
The finally block ensures that a handled exception (such as through ThreadExceptionDialog) doesn't permanently leave the state variable set to true. It's optional of course.
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