在树状视图中更改节点的检查状态很慢

Question

I have a Map control on a Form . The map control contains a collection of layers which each have a "IsVisible" to hide or show the layer.

I have a TreeView control with CheckBoxes with each node representing a layer, all contained under a single parent node .

When I check/uncheck a node, I want the related layer's IsVisible property to be set equal to the node's checked state.

Here's what I'm currently doing:

private void LayerTreeView_AfterCheck(object sender, TreeViewEventArgs e)
{
    if (e.Node.Parent == null) //if it's a parent node, make any children nodes match its checked state
    {
        foreach (TreeNode node in e.Node.Nodes)
        {
            node.Checked = e.Node.Checked;
            Map.BeginInvoke((MethodInvoker)delegate () { Map.FindFeatureLayer(node.Name).IsVisible = node.Checked; });
        }
    }
    else //it's a child node
    {
        Map.FindFeatureLayer(e.Node.Name).IsVisible = e.Node.Checked;
    }
    Map.BeginInvoke((MethodInvoker)delegate () { Map.Refresh(); }); //culprit is here
}

The problem is that there is a noticeable lag which increases with the more layers/nodes I have. In the code above, the last line contains the Map.Refresh();

The nodes don't update visibly until the Map.Refresh() is called, which is called for each node that has it's checked state changed. This causes the delay. I need the nodes to update immediately. It doesn't matter if the Map control lags behind with it's refresh, but it shouldn't be the opposite.

Answer 1

I think you need to rethink your design a bit. I assume Map is the TreeView control? Then you shouldn't need to use BeginInvoke to call its methods. All that does is push the call into the queue and delay the operation. As long as everything is on the UI thread, you shouldn't need to do that.

Keep in mind calling Refresh is going to cause the treeview to redraw the entire tree and ALL its nodes. That is a lot of work for every node change and may not be necessary if you don't invoke any changes. I also am not familiar with FindFeatureLayer so don't know how efficiently it works.

Finally, Microsoft documentation has a note about setting the Node.Checked property in the AfterCheck event.

Setting the TreeNode.Checked property from within the BeforeCheck or AfterCheck event
causes the event to be raised multiple times and can result in unexpected behavior. For
example, you might set the Checked property in the event handler when you are
recursively updating the child nodes so that the user does not have to expand and check
each one individually. To prevent the event from being raised multiple times, add logic
to your event handler that only executes your recursive code if the Action property of
the TreeViewEventArgs is not set to TreeViewAction.Unknown. For an example of how to do
this, see the Example section of the AfterCheck or BeforeCheck events.

so maybe this would be better???

if(e.Action != TreeViewAction.Unknown)
{
    if (e.Node.Parent == null) //if it's a parent node, make any children nodes match its checked state
    {
        foreach (TreeNode node in e.Node.Nodes)
        {
            node.Checked = e.Node.Checked;
            Map.FindFeatureLayer(node.Name).IsVisible = node.Checked;
        }
    }
    else //it's a child node
    {
        Map.FindFeatureLayer(e.Node.Name).IsVisible = e.Node.Checked;
    }
    //Map.Refresh();   // You may not need this if everything is immediate
}

hopefully that helps, I'm not able to fully test currently.