[Users] opacity slider in a bbar - trouble connecting to selected layer

[Eoin Mac Aoidh]

Hi list,
I have a tree containing the layers in my map. It has a bbar with a button to remove a selected layer from the map. Following this template, I am trying to also add in an opacity slider for the selected layer in the bbar: So that you can either remove a selected layer, or change its opacity.
I am having trouble connecting the slider to the selected layer. 
I suspect at least some of the problem is with the line:  

"layer: tree.getSelectionModel().getSelectedNode().layer"

I would appreciate any help regarding how to connect the selected layer with the slider.
Many Thanks,
Eoin

The following is the code I have:

var tree = new Ext.tree.TreePanel({
        region: "center",    //NBNBNBNB centER
        title: "Map Layers",
        width: 200,
        autoScroll: true,
        enableDD: true,
        lines: false,
        rootVisible: false,
        root: new GeoExt.tree.LayerContainer({
            layerStore: mapPanel.layers,
            expanded: true
        }),
        bbar: [{
            text: "Remove from Map",
            handler: function() {
                var node = tree.getSelectionModel().getSelectedNode();
                if(node) {
                    map.removeLayer(node.layer);
                }
            }
        },{
            xtype: "gx_opacityslider",
            layer: tree.getSelectionModel().getSelectedNode().layer,
            aggressive: true,
            horizontal: true,
            width: 120,
            plugins: new GeoExt.LayerOpacitySliderTip()
        }
         ]
      });







      
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