Add confirmation to SendableChooser (#1217)

This echos back the "selected" value to the "active" key to enable dashboards
to display positive feedback to the user that the value is actually set on
the robot side.

Also fixes SendableChooser so it can be safely added to multiple tables.
Changes to "selected" in any table will result in all "active" values being
updated.

Now that adding SendableChooser to multiple tables is supported, an ".instance"
key enables dashboards to treat the same SendableChooser as a common instance
if desired.

wpilibj/src/main/java/edu/wpi/first/wpilibj/smartdashboard/SendableChooser.java

@@ -7,7 +7,11 @@
 
 package edu.wpi.first.wpilibj.smartdashboard;
 
+import java.util.ArrayList;
 import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.ReentrantLock;
 
 import edu.wpi.first.networktables.NetworkTableEntry;
 import edu.wpi.first.wpilibj.SendableBase;
@@ -36,22 +40,33 @@ public class SendableChooser<V> extends SendableBase {
    * The key for the selected option.
    */
   private static final String SELECTED = "selected";
+  /**
+   * The key for the active option.
+   */
+  private static final String ACTIVE = "active";
   /**
    * The key for the option array.
    */
   private static final String OPTIONS = "options";
+  /**
+   * The key for the instance number.
+   */
+  private static final String INSTANCE = ".instance";
   /**
    * A map linking strings to the objects the represent.
    */
   @SuppressWarnings("PMD.LooseCoupling")
   private final LinkedHashMap<String, V> m_map = new LinkedHashMap<>();
   private String m_defaultChoice = "";
+  private final int m_instance;
+  private static final AtomicInteger s_instances = new AtomicInteger();
 
   /**
    * Instantiates a {@link SendableChooser}.
    */
   public SendableChooser() {
     super(false);
+    m_instance = s_instances.getAndIncrement();
   }
 
   /**
@@ -87,24 +102,60 @@ public class SendableChooser<V> extends SendableBase {
    * @return the option selected
    */
   public V getSelected() {
-    String selected = m_defaultChoice;
-    if (m_tableSelected != null) {
-      selected = m_tableSelected.getString(m_defaultChoice);
+    m_mutex.lock();
+    try {
+      if (m_selected != null) {
+        return m_map.get(m_selected);
+      } else {
+        return m_map.get(m_defaultChoice);
+      }
+    } finally {
+      m_mutex.unlock();
     }
-    return m_map.get(selected);
   }
 
-  private NetworkTableEntry m_tableSelected;
+  private String m_selected;
+  private final List<NetworkTableEntry> m_activeEntries = new ArrayList<>();
+  private final ReentrantLock m_mutex = new ReentrantLock();
 
   @Override
   public void initSendable(SendableBuilder builder) {
     builder.setSmartDashboardType("String Chooser");
+    builder.getEntry(INSTANCE).setDouble(m_instance);
     builder.addStringProperty(DEFAULT, () -> {
       return m_defaultChoice;
     }, null);
     builder.addStringArrayProperty(OPTIONS, () -> {
       return m_map.keySet().toArray(new String[0]);
     }, null);
-    m_tableSelected = builder.getEntry(SELECTED);
+    builder.addStringProperty(ACTIVE, () -> {
+      m_mutex.lock();
+      try {
+        if (m_selected != null) {
+          return m_selected;
+        } else {
+          return m_defaultChoice;
+        }
+      } finally {
+        m_mutex.unlock();
+      }
+    }, null);
+    m_mutex.lock();
+    try {
+      m_activeEntries.add(builder.getEntry(ACTIVE));
+    } finally {
+      m_mutex.unlock();
+    }
+    builder.addStringProperty(SELECTED, null, val -> {
+      m_mutex.lock();
+      try {
+        m_selected = val;
+        for (NetworkTableEntry entry : m_activeEntries) {
+          entry.setString(val);
+        }
+      } finally {
+        m_mutex.unlock();
+      }
+    });
   }
 }