Add focus listener to JSpinner text

This (mostly) ensures the text of a JSpinner is selected on focus. On OSX it
seems to always work with tabs, and mostly work with mouse clicking. However
there does seem to be a race condition where the text selection can be lost,
presumably from the JSPinner firing a validation event after the text field's
selection has been processed.

See #12 for future work.

src/main/java/org/scijava/ui/swing/widget/SwingNumberWidget.java

@@ -31,9 +31,12 @@
 package org.scijava.ui.swing.widget;
 
 import java.awt.Adjustable;
+import java.awt.Component;
 import java.awt.Dimension;
 import java.awt.event.AdjustmentEvent;
 import java.awt.event.AdjustmentListener;
+import java.awt.event.FocusEvent;
+import java.awt.event.FocusListener;
 import java.math.BigDecimal;
 import java.math.BigInteger;
 import java.text.DecimalFormat;
@@ -44,7 +47,9 @@
 import javax.swing.JScrollBar;
 import javax.swing.JSlider;
 import javax.swing.JSpinner;
+import javax.swing.JTextField;
 import javax.swing.SpinnerNumberModel;
+import javax.swing.SwingUtilities;
 import javax.swing.event.ChangeEvent;
 import javax.swing.event.ChangeListener;
 
@@ -121,6 +126,9 @@ else if (model.isStyle(NumberWidget.SLIDER_STYLE)) {
 		final SpinnerNumberModel spinnerModel =
 			new SpinnerNumberModelFactory().createModel(value, min, max, stepSize);
 		spinner = new JSpinner(spinnerModel);
+
+		fixSpinnerFocus();
+
 		fixSpinner(type);
 		setToolTip(spinner);
 		getComponent().add(spinner);
@@ -200,6 +208,43 @@ private void fixSpinner(final Class<?> type) {
 		}
 	}
 
+	/**
+	 * Adapted from <a href=
+	 * "http://stackoverflow.com/questions/20971050/jspinner-autoselect-onfocus"
+	 * >this SO post</a>.
+	 *
+	 * Tries to ensure that the text of a {@link JSpinner} is selected when it
+	 * has focus.
+	 */
+	private void fixSpinnerFocus() {
+		for (final Component c : spinner.getEditor().getComponents()) {
+			if (JTextField.class.isAssignableFrom(c.getClass())) {
+				c.addFocusListener(new FocusListener() {
+
+					@Override
+					public void focusGained(final FocusEvent e) {
+						queueSelection();
+					}
+
+					@Override
+					public void focusLost(final FocusEvent e) {
+						queueSelection();
+					}
+
+					private void queueSelection() {
+						SwingUtilities.invokeLater(new Runnable() {
+							@Override
+							public void run() {
+								((JTextField) c).selectAll();
+							}
+						});
+					}
+
+				});
+			}
+		}
+	}
+
 	/** Sets slider values to match the spinner. */
 	private void syncSliders() {
 		if (slider != null) {