Improve dialog

* Focus on row spinner upon opening of the settings dialog.
* Select the content of the spinner fields when they gain focues.
* Update preview when field contents change

Fixes #6.

src/nl/jeroenhoek/josm/gridify/ui/GridSizePanel.java

@@ -26,8 +26,8 @@ public GridSizePanel(ChangeCallback changeCallback, int rows, int columns) {
         this.columns = columns;
         setLayout(new BoxLayout(this, BoxLayout.X_AXIS));
 
-        spinnerRows = new PositiveSpinner(rows);
-        spinnerColumns = new PositiveSpinner(columns);
+        spinnerRows = new PositiveSpinner(rows, this::setRowCount);
+        spinnerColumns = new PositiveSpinner(columns, this::setColumnCount);
         JLabel xLabel = new JLabel("×");
         xLabel.setFont(new Font("Monospaced", Font.PLAIN, 18));
 
@@ -70,6 +70,11 @@ void nudgeColumnCount(Nudge direction) {
         }
     }
 
+    @Override
+    public boolean requestFocusInWindow() {
+        return this.spinnerRows.requestFocusInWindow();
+    }
+
     public int getRowCount() {
         return this.rows;
     }

src/nl/jeroenhoek/josm/gridify/ui/GridifySettingsDialog.java

@@ -111,6 +111,8 @@ public void setupDialog() {
         setDefaultButton(1);
 
         super.setupDialog();
+
+        gridSizePanel.requestFocusInWindow();
     }
 
     @Override

src/nl/jeroenhoek/josm/gridify/ui/PositiveSpinner.java

@@ -1,20 +1,29 @@
 // License: GPL. For details, see LICENSE file.
 package nl.jeroenhoek.josm.gridify.ui;
 
-import javax.swing.JFormattedTextField;
-import javax.swing.JSpinner;
-import javax.swing.SpinnerNumberModel;
-import java.awt.Dimension;
-import java.awt.Font;
+import javax.swing.*;
+import javax.swing.event.DocumentEvent;
+import javax.swing.event.DocumentListener;
+import java.awt.*;
+import java.awt.event.FocusEvent;
+import java.text.ParseException;
+import java.util.Objects;
 
 /**
  * A {@link JSpinner} limited to a range of 1 to 1000. This class also adds a mouse wheel listener allowing users to
  * scroll the value up or down.
  */
 public class PositiveSpinner extends JSpinner {
-    public PositiveSpinner(int defaultValue) {
+
+    private final JFormattedTextField field;
+    private final ValueChanged changeCallback;
+    private Integer lastValue;
+
+    public PositiveSpinner(int defaultValue, ValueChanged changeCallback) {
         super(new SpinnerNumberModel(defaultValue, 1, 1000, 1));
-        JFormattedTextField field = ((DefaultEditor) getEditor()).getTextField();
+        this.changeCallback = changeCallback;
+        DefaultEditor editor = (DefaultEditor) getEditor();
+        field = editor.getTextField();
         field.setColumns(3);
         field.setFont(new Font("Monospaced", Font.PLAIN, 18));
 
@@ -40,10 +49,88 @@ public PositiveSpinner(int defaultValue) {
                 setValue(newValue);
             }
         });
+
+        // Select the input for easy editing when the field receives focus.
+        field.addFocusListener(new FocusListener());
+
+        // Let our parent know when the field value changes for live updates.
+        field.getDocument().addDocumentListener(new DocumentListener() {
+            @Override
+            public void insertUpdate(DocumentEvent e) {
+                callbackIfChanged();
+            }
+
+            @Override
+            public void removeUpdate(DocumentEvent e) {
+                callbackIfChanged();
+            }
+
+            @Override
+            public void changedUpdate(DocumentEvent e) {
+                callbackIfChanged();
+            }
+        });
+
+        this.lastValue = (Integer) getValue();
+    }
+
+    void callbackIfChanged() {
+        Integer newValue;
+        try {
+            newValue = Integer.parseInt(field.getText());
+        } catch (NumberFormatException e) {
+            // Ignore.
+            return;
+        }
+
+        if (!Objects.equals(newValue, lastValue)) {
+            SwingUtilities.invokeLater(() -> {
+                this.lastValue = newValue;
+                changeCallback.onChange(newValue);
+            });
+        }
     }
 
     @Override
     public Dimension getMaximumSize() {
         return getPreferredSize();
     }
+
+    @Override
+    public boolean requestFocusInWindow() {
+        return this.field.requestFocusInWindow();
+    }
+
+    /**
+     * This should work on most platforms.
+     */
+    static class FocusListener implements java.awt.event.FocusListener {
+        // Thanks to mKorbel (https://stackoverflow.com/users/714968/mkorbel) for this instructive snippet:
+        // https://stackoverflow.com/questions/20971050/jspinner-autoselect-onfocus/20971713#20971713
+
+        @Override
+        public void focusGained(FocusEvent e) {
+            focus(e);
+        }
+
+        @Override
+        public void focusLost(FocusEvent e) {
+            focus(e);
+        }
+
+        private void focus(FocusEvent e) {
+            final Component component = e.getComponent();
+            if (component instanceof JFormattedTextField) {
+                JFormattedTextField field = (JFormattedTextField) component;
+                SwingUtilities.invokeLater(() -> {
+                    field.setText(field.getText());
+                    field.selectAll();
+                });
+            }
+        }
+    }
+
+    interface ValueChanged {
+        void onChange(int value);
+    }
 }