Index: /applications/editors/josm/plugins/wmsplugin/src/wmsplugin/WMSAdjustAction.java
===================================================================
--- /applications/editors/josm/plugins/wmsplugin/src/wmsplugin/WMSAdjustAction.java	(revision 22760)
+++ /applications/editors/josm/plugins/wmsplugin/src/wmsplugin/WMSAdjustAction.java	(revision 22761)
@@ -3,14 +3,28 @@
 import static org.openstreetmap.josm.tools.I18n.tr;
 
+import java.awt.Component;
 import java.awt.Cursor;
+import java.awt.GridBagLayout;
 import java.awt.event.MouseEvent;
 import java.awt.event.MouseListener;
 import java.awt.event.MouseMotionListener;
+import java.util.List;
+
+import javax.swing.DefaultComboBoxModel;
+import javax.swing.DefaultListCellRenderer;
+import javax.swing.Icon;
+import javax.swing.JComboBox;
+import javax.swing.JLabel;
+import javax.swing.JList;
+import javax.swing.JOptionPane;
+import javax.swing.JPanel;
 
 import org.openstreetmap.josm.Main;
 import org.openstreetmap.josm.actions.mapmode.MapMode;
 import org.openstreetmap.josm.data.coor.EastNorth;
+import org.openstreetmap.josm.gui.ExtendedDialog;
 import org.openstreetmap.josm.gui.MapFrame;
 import org.openstreetmap.josm.gui.layer.Layer;
+import org.openstreetmap.josm.tools.GBC;
 import org.openstreetmap.josm.tools.ImageProvider;
 
@@ -34,8 +48,16 @@
 	@Override public void enterMode() {
 		super.enterMode();
-		if (!Main.isDisplayingMapView() || !(Main.map.mapView.getActiveLayer() instanceof WMSLayer)) {
+		if (!hasWMSLayersToAdjust()) {
+			warnNoWMSLayers();
 			return;
 		}
-		adjustingLayer = (WMSLayer) Main.map.mapView.getActiveLayer();
+		List<WMSLayer> wmsLayers = Main.map.mapView.getLayersOfType(WMSLayer.class);
+		if (wmsLayers.size() == 1) {
+			adjustingLayer = wmsLayers.get(0);
+		} else {
+			adjustingLayer = (WMSLayer)askAdjustLayer(Main.map.mapView.getLayersOfType(WMSLayer.class));
+		}
+		if (adjustingLayer == null)
+			return;
 		if (!adjustingLayer.isVisible()) {
 			adjustingLayer.setVisible(true);
@@ -101,9 +123,94 @@
 	}
 
-	// This only makes the buttons look disabled, but since no keyboard shortcut is
-	// provided there aren't any other means to activate this tool
 	@Override public boolean layerIsSupported(Layer l) {
-		return l instanceof WMSLayer;
-	}
-
+		return hasWMSLayersToAdjust();
+	}
+
+	/**
+	 * the list cell renderer used to render layer list entries
+	 *
+	 */
+	static public class LayerListCellRenderer extends DefaultListCellRenderer {
+
+		protected boolean isActiveLayer(Layer layer) {
+			if (Main.map == null)
+				return false;
+			if (Main.map.mapView == null)
+				return false;
+			return Main.map.mapView.getActiveLayer() == layer;
+		}
+
+		@Override
+		public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected,
+				boolean cellHasFocus) {
+			Layer layer = (Layer) value;
+			JLabel label = (JLabel) super.getListCellRendererComponent(list, layer.getName(), index, isSelected,
+					cellHasFocus);
+			Icon icon = layer.getIcon();
+			label.setIcon(icon);
+			label.setToolTipText(layer.getToolTipText());
+			return label;
+		}
+	}
+
+	/**
+	 * Prompts the user with a list of WMS layers which can be adjusted
+	 *
+	 * @param adjustableLayers the list of adjustable layers
+	 * @return  the selected layer; null, if no layer was selected
+	 */
+	protected Layer askAdjustLayer(List<? extends Layer> adjustableLayers) {
+		JComboBox layerList = new JComboBox();
+		layerList.setRenderer(new LayerListCellRenderer());
+		layerList.setModel(new DefaultComboBoxModel(adjustableLayers.toArray()));
+		layerList.setSelectedIndex(0);
+
+		JPanel pnl = new JPanel();
+		pnl.setLayout(new GridBagLayout());
+		pnl.add(new JLabel(tr("Please select the WMS layer to adjust.")), GBC.eol());
+		pnl.add(layerList, GBC.eol());
+
+		ExtendedDialog diag = new ExtendedDialog(
+				Main.parent,
+				tr("Select WMS layer"),
+				new String[] { tr("Start adjusting"),tr("Cancel") }
+		);
+		diag.setContent(pnl);
+		diag.setButtonIcons(new String[] { "mapmode/adjustwms", "cancel" });
+		diag.showDialog();
+		int decision = diag.getValue();
+		if (decision != 1)
+			return null;
+		Layer adjustLayer = (Layer) layerList.getSelectedItem();
+		return adjustLayer;
+	}
+
+	/**
+	 * Displays a warning message if there are no WMS layers to adjust
+	 *
+	 */
+	protected void warnNoWMSLayers() {
+		JOptionPane.showMessageDialog(
+				Main.parent,
+				tr("There are currently no WMS layer to adjust."),
+				tr("No layers to adjust"),
+				JOptionPane.WARNING_MESSAGE
+		);
+	}
+
+	/**
+	 * Replies true if there is at least one WMS layer
+	 *
+	 * @return true if there is at least one WMS layer
+	 */
+	protected boolean hasWMSLayersToAdjust() {
+		if (Main.map == null) return false;
+		if (Main.map.mapView == null) return false;
+		return ! Main.map.mapView.getLayersOfType(WMSLayer.class).isEmpty();
+	}
+
+	@Override
+	protected void updateEnabledState() {
+		setEnabled(hasWMSLayersToAdjust());
+	}
 }