Add on-hover selection on Board/Library manager

User testing on skilled devs showed that "buttons appear on click" behaviour is far from being understood.
Accessibility features (like moving with Arrow keys) should be untouched.

app/src/cc/arduino/contributions/libraries/ui/ContributedLibraryTableCellEditor.java

@@ -76,9 +76,12 @@ public class ContributedLibraryTableCellEditor extends InstallerTableCell {
       ContributedLibrary lib = (ContributedLibrary) chooser.getSelectedItem();
       onInstall(lib, editorValue.getInstalled());
     });
-    editorCell.versionToInstallChooser.addItemListener(e -> editorValue
+    editorCell.versionToInstallChooser.addActionListener(e -> {
-        .select((ContributedLibrary) editorCell.versionToInstallChooser
+      editorValue.select((ContributedLibrary) editorCell.versionToInstallChooser.getSelectedItem());
-            .getSelectedItem()));
+      if (editorCell.versionToInstallChooser.getSelectedIndex() != 0) {
+        InstallerTableCell.dropdownSelected(true);
+      }
+    });
 
     setEnabled(true);
 

app/src/cc/arduino/contributions/libraries/ui/ContributedLibraryTableCellJPanel.java

@@ -54,10 +54,13 @@ public class ContributedLibraryTableCellJPanel extends JPanel {
     downgradeChooser.addItem("-");
     downgradeChooser.setMaximumSize(new Dimension((int)downgradeChooser.getPreferredSize().getWidth() + 50, (int)downgradeChooser.getPreferredSize().getHeight()));
     downgradeChooser.setMinimumSize(new Dimension((int)downgradeChooser.getPreferredSize().getWidth() + 50, (int)downgradeChooser.getPreferredSize().getHeight()));
-    downgradeChooser.addItemListener(e -> {
+    downgradeChooser.addActionListener(e -> {
       Object selectVersionItem = downgradeChooser.getItemAt(0);
-      boolean disableDowngrade = (e.getItem() == selectVersionItem);
+      boolean disableDowngrade = (downgradeChooser.getSelectedItem() == selectVersionItem);
       downgradeButton.setEnabled(!disableDowngrade);
+      if (!disableDowngrade) {
+        InstallerTableCell.dropdownSelected(true);
+      }
     });
 
     versionToInstallChooser = new JComboBox();

app/src/cc/arduino/contributions/libraries/ui/LibraryManagerUI.java

@@ -117,6 +117,7 @@ public class LibraryManagerUI extends InstallerJDialog<ContributedLibrary> {
     @Override
     public void actionPerformed(ActionEvent event) {
       DropdownItem<ContributedLibrary> selected = (DropdownItem<ContributedLibrary>) typeChooser.getSelectedItem();
+      previousRowAtPoint = -1;
       if (typeFilter == null || !typeFilter.equals(selected)) {
         typeFilter = selected.getFilterPredicate();
         if (contribTable.getCellEditor() != null) {

app/src/cc/arduino/contributions/packages/ui/ContributedPlatformTableCellEditor.java

@@ -74,9 +74,12 @@ public class ContributedPlatformTableCellEditor extends InstallerTableCell {
           .getSelectedItem();
       onInstall(selected, value.getInstalled());
     });
-    cell.versionToInstallChooser.addItemListener(e -> value
+    cell.versionToInstallChooser.addActionListener(e -> {
-        .select((ContributedPlatform) cell.versionToInstallChooser
+      value.select((ContributedPlatform) cell.versionToInstallChooser.getSelectedItem());
-            .getSelectedItem()));
+      if (cell.versionToInstallChooser.getSelectedIndex() != 0) {
+        InstallerTableCell.dropdownSelected(true);
+      }
+    });
 
     setEnabled(true);
 

app/src/cc/arduino/contributions/packages/ui/ContributedPlatformTableCellJPanel.java

@@ -98,6 +98,9 @@ public class ContributedPlatformTableCellJPanel extends JPanel {
       Object selectVersionItem = downgradeChooser.getItemAt(0);
       boolean disableDowngrade = (e.getItem() == selectVersionItem);
       downgradeButton.setEnabled(!disableDowngrade);
+      if (!disableDowngrade) {
+        InstallerTableCell.dropdownSelected(true);
+      }
     });
 
     versionToInstallChooser = new JComboBox();

app/src/cc/arduino/contributions/ui/InstallerJDialog.java

@@ -43,6 +43,8 @@ import java.awt.event.FocusEvent;
 import java.awt.event.FocusListener;
 import java.awt.event.KeyEvent;
 import java.awt.event.WindowEvent;
+import java.awt.event.MouseEvent;
+import java.awt.event.MouseMotionListener;
 import java.util.function.Predicate;
 import java.util.stream.Stream;
 
@@ -88,6 +90,8 @@ public abstract class InstallerJDialog<T> extends JDialog {
   private final JButton closeButton;
   private final JButton dismissErrorMessageButton;
 
+  protected int previousRowAtPoint = -1;
+
   abstract protected FilteredAbstractTableModel<T> createContribModel();
 
   abstract protected TableCellRenderer createCellRenderer();
@@ -118,6 +122,7 @@ public abstract class InstallerJDialog<T> extends JDialog {
       filterField = new FilterJTextField(tr("Filter your search...")) {
         @Override
         protected void onFilter(String[] _filters) {
+          previousRowAtPoint = -1;
           filters = _filters;
           if (contribTable.getCellEditor() != null) {
             contribTable.getCellEditor().stopCellEditing();
@@ -167,6 +172,25 @@ public abstract class InstallerJDialog<T> extends JDialog {
       }
     });
 
+    contribTable.addMouseMotionListener(new MouseMotionListener() {
+
+        public void mouseDragged(MouseEvent e) {}
+
+        public void mouseMoved(MouseEvent e) {
+            // avoid firing edits events until the mouse changes cell or the user is back on the cell after selecting a dropdown
+            int rowAtPoint = contribTable.rowAtPoint(e.getPoint());
+            if (!InstallerTableCell.isDropdownSelected() && rowAtPoint != previousRowAtPoint) {
+              contribTable.editCellAt(rowAtPoint, 0);
+              previousRowAtPoint = rowAtPoint;
+              InstallerTableCell.dropdownSelected(false);
+            }
+            if (InstallerTableCell.isDropdownSelected() && rowAtPoint == previousRowAtPoint) {
+              // back to the original cell, can drop dropdown selector lock
+              InstallerTableCell.dropdownSelected(false);
+            }
+        }
+    });
+
     {
       TableColumnModel tcm = contribTable.getColumnModel();
       TableColumn col = tcm.getColumn(0);
@@ -286,6 +310,7 @@ public abstract class InstallerJDialog<T> extends JDialog {
     @Override
     public void actionPerformed(ActionEvent event) {
       DropdownItem<T> selected = (DropdownItem<T>) categoryChooser.getSelectedItem();
+      previousRowAtPoint = -1;
       if (categoryFilter == null || !categoryFilter.equals(selected)) {
         categoryFilter = selected.getFilterPredicate();
         if (contribTable.getCellEditor() != null) {

app/src/cc/arduino/contributions/ui/InstallerTableCell.java

@@ -41,6 +41,16 @@ public abstract class InstallerTableCell extends AbstractCellEditor implements T
 
   abstract public void setEnabled(boolean b);
 
+  private static boolean dropdownSelected = false;
+
+  public static boolean isDropdownSelected( ) {
+    return dropdownSelected;
+  }
+
+  public static void dropdownSelected(boolean b) {
+    dropdownSelected = b;
+  }
+
   abstract public void setStatus(String s);
   
   public static void setJTextPaneDimensionToFitContainedText(JTextPane jTextPane, int width) {