DisplayTopology: user cannot drag only display

When dragging a single display, we don't constrain the position of the
display, and the user can drag it anywhere on the fragment. As such we
need to either prevent the drag or refresh the pane always if there is
only one display. This CL chooses the former.

Flag: com.android.settings.flags.display_topology_pane_in_display_list
Test: atest DisplayTopologyPreferenceTest.kt
Bug: b/352650922
Change-Id: Icb101b734ce9b88435f64a71bf77f878f9b230e0

src/com/android/settings/connecteddevice/display/DisplayTopology.kt

@@ -404,8 +404,12 @@ class DisplayTopologyPreference(context : Context)
 
     private fun onBlockTouchDown(
             displayId: Int, displayPos: RectF, block: DisplayBlock, ev: MotionEvent): Boolean {
-        val stationaryDisps = (mTopologyInfo ?: return false)
-                .positions.filter { it.first != displayId }
+        val positions = (mTopologyInfo ?: return false).positions
+
+        // Do not allow dragging for single-display topology, since there is nothing to clamp it to.
+        if (positions.size <= 1) { return false }
+
+        val stationaryDisps = positions.filter { it.first != displayId }
 
         // We have to use rawX and rawY for the coordinates since the view receiving the event is
         // also the view that is moving. We need coordinates relative to something that isn't

tests/robotests/src/com/android/settings/connecteddevice/display/DisplayTopologyPreferenceTest.kt

@@ -102,6 +102,15 @@ class DisplayTopologyPreferenceTest {
                 .map { preference.mPaneContent.getChildAt(it) as DisplayBlock }
                 .toList()
 
+    fun singleDisplayTopology(): DisplayTopology {
+        val primaryId = 22;
+
+        val root = DisplayTopology.TreeNode(
+                primaryId, /* width= */ 200f, /* height= */ 160f, POSITION_LEFT, /* offset= */ 0f)
+
+        return DisplayTopology(root, primaryId)
+    }
+
     fun twoDisplayTopology(childPosition: Int, childOffset: Float): DisplayTopology {
         val primaryId = 1
 
@@ -287,6 +296,36 @@ class DisplayTopologyPreferenceTest {
         assertThat(preference.mTimesReceivedSameTopology).isEqualTo(1)
     }
 
+    @Test
+    fun cannotMoveSingleDisplay() {
+        injector.topology = singleDisplayTopology()
+        preparePane()
+
+        val paneChildren = getPaneChildren()
+        assertThat(paneChildren).hasSize(1)
+        val block = paneChildren[0]
+
+        val origY = block.unpaddedY
+
+        block.dispatchTouchEvent(MotionEventBuilder.newBuilder()
+                .setAction(MotionEvent.ACTION_DOWN)
+                .setPointer(0f, 0f)
+                .build())
+        block.dispatchTouchEvent(MotionEventBuilder.newBuilder()
+                .setAction(MotionEvent.ACTION_MOVE)
+                .setPointer(0f, 30f)
+                .build())
+
+        assertThat(block.unpaddedY).isWithin(0.01f).of(origY)
+
+        block.dispatchTouchEvent(MotionEventBuilder.newBuilder()
+                .setAction(MotionEvent.ACTION_UP)
+                .build())
+
+        // Block should be back to original position.
+        assertThat(block.unpaddedY).isWithin(0.01f).of(origY)
+    }
+
     @Test
     fun updatedTopologyCancelsDragIfNonTrivialChange() {
         val (leftBlock, rightBlock) = setupTwoDisplays(POSITION_LEFT, /* childOffset= */ 42f)