Undo button works, except doesn't signify disabled

app/src/main/java/edu/liu/floodgame/GridActivity.java

@@ -7,10 +7,12 @@ import android.support.annotation.Nullable;
 import android.support.v7.app.AppCompatActivity;
 import android.support.v7.widget.GridLayout;
 import android.view.View;
+import android.widget.ImageButton;
 import android.widget.LinearLayout;
 import android.widget.TextView;
 
 import java.util.Random;
+import java.util.Stack;
 
 public class GridActivity extends AppCompatActivity implements FloodGrid {
 
@@ -24,15 +26,18 @@ public class GridActivity extends AppCompatActivity implements FloodGrid {
     private GridLayout gridLayout;
     private LinearLayout buttonBar;
     private TextView numMovesText;
+    private ImageButton undoButton;
     private int numColors;
     private int numMoves = 0;
     private boolean gameOver = false;
+    private Stack<int[]> history = new Stack<>();
 
     @Override
     protected void onCreate(@Nullable Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_flood_grid);
         numMovesText = findViewById(R.id.num_moves);
+        undoButton = findViewById(R.id.undoButton);
 
         // Grab palette
         Intent intent = getIntent();
@@ -69,7 +74,7 @@ public class GridActivity extends AppCompatActivity implements FloodGrid {
             gameOver = FloodGridOps.gameOver(this);
             setNumMoves(savedInstanceState.getInt(NUM_MOVES_KEY));
         }
-
+        undoButton.setEnabled(history.size() > 0);
         recordNeighborsThroughout();
     }
 
@@ -169,20 +174,32 @@ public class GridActivity extends AppCompatActivity implements FloodGrid {
         }
     }
 
+    public void onClickUndo(View v) {
+        FloodGridOps.fromArray(this, history.pop());
+        gameOver = false;
+        setNumMoves(numMoves-1);
+        undoButton.setEnabled(history.size() > 0);
+        recordNeighborsThroughout();
+    }
+
     public void onClickColor(int color) {
         if(gameOver) {
             // Clicking when game already over restarts
             FloodGridOps.randomize(this, new Random(), numColors);
             gameOver = false;
             setNumMoves(0);
+            history.clear();
+            undoButton.setEnabled(false);
         }
         else {
+            history.push(FloodGridOps.toArray(this));
             FloodGridOps.flood(this, color);
             if (FloodGridOps.gameOver(this)) {
                 gameOver = true;
             }
             setNumMoves(numMoves + 1);
         }
+        undoButton.setEnabled(history.size() > 0);
         recordNeighborsThroughout();
     }
 

app/src/main/res/layout-land/activity_flood_grid.xml

@@ -87,4 +87,21 @@
         app:layout_constraintStart_toEndOf="@+id/grid"
         app:layout_constraintTop_toBottomOf="@+id/grid" />
 
+    <ImageButton
+        android:id="@+id/undoButton"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginStart="8dp"
+        android:layout_marginLeft="8dp"
+        android:layout_marginTop="8dp"
+        android:layout_marginEnd="8dp"
+        android:layout_marginRight="8dp"
+        android:layout_marginBottom="8dp"
+        android:onClick="onClickUndo"
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintEnd_toStartOf="@+id/buttonBar"
+        app:layout_constraintStart_toEndOf="@+id/grid"
+        app:layout_constraintTop_toBottomOf="@+id/num_moves"
+        app:srcCompat="@android:drawable/ic_menu_revert" />
+
 </android.support.constraint.ConstraintLayout>
\ No newline at end of file

app/src/main/res/layout/activity_flood_grid.xml

@@ -85,4 +85,21 @@
         app:layout_constraintTop_toBottomOf="@+id/grid"
         app:layout_constraintVertical_bias="0.341" />
 
+    <ImageButton
+        android:id="@+id/undoButton"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_marginStart="8dp"
+        android:layout_marginLeft="8dp"
+        android:layout_marginTop="8dp"
+        android:layout_marginEnd="8dp"
+        android:layout_marginRight="8dp"
+        android:layout_marginBottom="8dp"
+        android:onClick="onClickUndo"
+        app:layout_constraintBottom_toTopOf="@+id/buttonBar"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@+id/num_moves"
+        app:srcCompat="@android:drawable/ic_menu_revert" />
+
 </android.support.constraint.ConstraintLayout>
\ No newline at end of file