Add drop listener sample test (#4204)

Author: shai-almog

maven/core-unittests/src/test/java/com/codename1/ui/DropListenerSampleTest.java

@@ -0,0 +1,110 @@
+package com.codename1.ui;
+
+import com.codename1.junit.FormTest;
+import com.codename1.junit.UITestBase;
+import com.codename1.ui.events.ActionEvent;
+import com.codename1.ui.geom.Dimension;
+import com.codename1.ui.layouts.GridLayout;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * Port of the DropListenerSample demo into a regression test that fires drag and drop
+ * events through the full Codename One stack using {@link TestCodenameOneImplementation}.
+ */
+class DropListenerSampleTest extends UITestBase {
+
+    @FormTest
+    void dropListenerReceivesDropEventsAndDelegatesToTarget() {
+        implementation.setBuiltinSoundsEnabled(false);
+        Form form = Display.getInstance().getCurrent();
+        form.setLayout(new GridLayout(1, 2));
+
+        TrackingContainer draggable = new TrackingContainer();
+        draggable.setPreferredSize(new Dimension(80, 80));
+        draggable.setDraggable(true);
+
+        TrackingDropTarget dropTarget = new TrackingDropTarget();
+        dropTarget.setPreferredSize(new Dimension(80, 80));
+        dropTarget.setDropTarget(true);
+
+        form.add(draggable);
+        form.add(dropTarget);
+        form.revalidate();
+
+        assertTrue(draggable.getWidth() > 0 && draggable.getHeight() > 0,
+                "Draggable component should have layout dimensions");
+        assertTrue(dropTarget.getWidth() > 0 && dropTarget.getHeight() > 0,
+                "Drop target should have layout dimensions");
+
+        final int[] dropListenerCount = {0};
+        final ActionEvent[] lastEvent = {null};
+        draggable.addDropListener(evt -> {
+            dropListenerCount[0]++;
+            lastEvent[0] = evt;
+        });
+
+        int startX = draggable.getAbsoluteX() + draggable.getWidth() / 2;
+        int startY = draggable.getAbsoluteY() + draggable.getHeight() / 2;
+        int targetX = dropTarget.getAbsoluteX() + dropTarget.getWidth() / 2;
+        int targetY = dropTarget.getAbsoluteY() + dropTarget.getHeight() / 2;
+
+        implementation.dispatchPointerPress(startX, startY);
+        implementation.dispatchPointerDrag(startX + draggable.getWidth() / 4, startY);
+        implementation.dispatchPointerDrag(startX + draggable.getWidth() / 3, startY + draggable.getHeight() / 6);
+        implementation.dispatchPointerDrag((startX + targetX) / 2, (startY + targetY) / 2);
+        implementation.dispatchPointerDrag(targetX, targetY);
+        implementation.dispatchPointerDrag(targetX, targetY + dropTarget.getHeight() / 4);
+        implementation.dispatchPointerRelease(targetX, targetY);
+
+        assertTrue(dropListenerCount[0] > 0, "Drop listener should be invoked when dropping on a target");
+        assertNotNull(lastEvent[0], "Drop event should be captured");
+        assertEquals(dropTarget, lastEvent[0].getComponent(), "Drop listener should receive the drop target component");
+        assertEquals(draggable, lastEvent[0].getSource(), "Source component should be the draggable container");
+        assertTrue(dropTarget.getDragOverCount() > 0, "Drag over callbacks should occur on the drop target");
+        assertEquals(1, dropTarget.getDropCount(), "Drop target should be notified exactly once");
+        assertEquals(draggable, dropTarget.getLastDragged(), "Drop target should receive the dragged component instance");
+    }
+
+    private static class TrackingContainer extends Container {
+        TrackingContainer() {
+            getStyle().setBgTransparency(255);
+        }
+    }
+
+    private static class TrackingDropTarget extends Container {
+        private int dropCount;
+        private Component lastDragged;
+        private int dragOverCount;
+
+        TrackingDropTarget() {
+            getStyle().setBgTransparency(255);
+        }
+
+        @Override
+        protected boolean draggingOver(Component dragged, int x, int y) {
+            dragOverCount++;
+            return super.draggingOver(dragged, x, y);
+        }
+
+        @Override
+        public void drop(Component dragged, int x, int y) {
+            dropCount++;
+            lastDragged = dragged;
+        }
+
+        int getDropCount() {
+            return dropCount;
+        }
+
+        Component getLastDragged() {
+            return lastDragged;
+        }
+
+        int getDragOverCount() {
+            return dragOverCount;
+        }
+    }
+}