Preventing multiple repeat selection of synchronized Controls ?
- by BillW
The working code sample here synchronizes (single) selection in a TreeView, ListView, and ComboBox via the use of lambda expressions in a dictionary where the Key in the dictionary is a Control, and the Value of each Key is an Action<int.
Where I am stuck is that I am getting multiple repetitions of execution of the code that sets the selection in the various controls in a way that's unexpected : it's not recursing : there's no StackOverFlow error happening; but, I would like to figure out why the current strategy for preventing multiple selection of the same controls is not working.
Perhaps the real problem here is distinguishing between a selection update triggered by the end-user and a selection update triggered by the code that synchronizes the other controls ?
Note: I've been experimenting with using Delegates, and forms of Delegates like Action<T>, to insert executable code in Dictionaries : I "learn best" by posing programming "challenges" to myself, and implementing them, as well as studying, at the same time, the "golden words" of luminaries like Skeet, McDonald, Liberty, Troelsen, Sells, Richter.
Note: Appended to this question/code, for "deep background," is a statement of how I used to do things in pre C#3.0 days where it seemed like I did need to use explicit measures to prevent recursion when synchronizing selection.
Code : Assume a WinForms standard TreeView, ListView, ComboBox, all with the same identical set of entries (i.e., the TreeView has only root nodes; the ListView, in Details View, has one Column).
private Dictionary<Control, Action<int>> ControlToAction = new Dictionary<Control, Action<int>>();
private void Form1_Load(object sender, EventArgs e)
{
// add the Controls to be synchronized to the Dictionary
// with appropriate Action<int> lambda expressions
ControlToAction.Add(treeView1, (i => { treeView1.SelectedNode = treeView1.Nodes[i]; }));
ControlToAction.Add(listView1, (i => { listView1.Items[i].Selected = true; }));
ControlToAction.Add(comboBox1, (i => { comboBox1.SelectedIndex = i; }));
}
private void synchronizeSelection(int i, Control currentControl)
{
foreach(Control theControl in ControlToAction.Keys)
{
// skip the 'current control'
if (theControl == currentControl) continue;
// for debugging only
Console.WriteLine(theControl.Name + " synchronized");
// execute the Action<int> associated with the Control
ControlToAction[theControl](i);
}
}
private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)
{
synchronizeSelection(e.Node.Index, treeView1);
}
private void listView1_SelectedIndexChanged(object sender, EventArgs e)
{
// weed out ListView SelectedIndexChanged firing
// with SelectedIndices having a Count of #0
if (listView1.SelectedIndices.Count > 0)
{
synchronizeSelection(listView1.SelectedIndices[0], listView1);
}
}
private void comboBox1_SelectedValueChanged(object sender, EventArgs e)
{
if (comboBox1.SelectedIndex > -1)
{
synchronizeSelection(comboBox1.SelectedIndex, comboBox1);
}
}
background : pre C# 3.0
Seems like, back in pre C# 3.0 days, I was always using a boolean flag to prevent recursion when multiple controls were updated. For example, I'd typically have code like this for synchronizing a TreeView and ListView : assuming each Item in the ListView was synchronized with a root-level node of the TreeView via a common index :
// assume ListView is in 'Details View,' has a single column,
// MultiSelect = false
// FullRowSelect = true
// HideSelection = false;
// assume TreeView
// HideSelection = false
// FullRowSelect = true
// form scoped variable
private bool dontRecurse = false;
private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)
{
if(dontRecurse) return;
dontRecurse = true;
listView1.Items[e.Node.Index].Selected = true;
dontRecurse = false;
}
private void listView1_SelectedIndexChanged(object sender, EventArgs e)
{
if(dontRecurse) return
// weed out ListView SelectedIndexChanged firing
// with SelectedIndices having a Count of #0
if (listView1.SelectedIndices.Count > 0)
{
dontRecurse = true;
treeView1.SelectedNode = treeView1.Nodes[listView1.SelectedIndices[0]];
dontRecurse = false;
}
}
Then it seems, somewhere around FrameWork 3~3.5, I could get rid of the code to suppress recursion, and there was was no recursion (at least not when synchronizing a TreeView and a ListView). By that time it had become a "habit" to use a boolean flag to prevent recursion, and that may have had to do with using a certain third party control.
