remove top padding when system UI in fullscreen mode (#17985)

shell/platform/android/io/flutter/embedding/android/FlutterView.java

@@ -400,10 +400,11 @@ public class FlutterView extends FrameLayout {
   @SuppressLint({"InlinedApi", "NewApi"})
   @NonNull
   public final WindowInsets onApplyWindowInsets(@NonNull WindowInsets insets) {
+    boolean statusBarHidden = (SYSTEM_UI_FLAG_FULLSCREEN & getWindowSystemUiVisibility()) != 0;
     WindowInsets newInsets = super.onApplyWindowInsets(insets);
 
     // Status bar (top) and left/right system insets should partially obscure the content (padding).
-    viewportMetrics.paddingTop = insets.getSystemWindowInsetTop();
+    viewportMetrics.paddingTop = statusBarHidden ? 0 : insets.getSystemWindowInsetTop();
     viewportMetrics.paddingRight = insets.getSystemWindowInsetRight();
     viewportMetrics.paddingBottom = 0;
     viewportMetrics.paddingLeft = insets.getSystemWindowInsetLeft();

shell/platform/android/test/io/flutter/embedding/android/FlutterViewTest.java

@@ -8,9 +8,13 @@ import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
+import android.annotation.TargetApi;
 import android.content.Context;
 import android.content.res.Configuration;
 import android.content.res.Resources;
+import android.view.View;
+import android.view.ViewGroup;
+import android.view.WindowInsets;
 import io.flutter.embedding.engine.FlutterEngine;
 import io.flutter.embedding.engine.FlutterJNI;
 import io.flutter.embedding.engine.loader.FlutterLoader;
@@ -21,6 +25,7 @@ import java.util.concurrent.atomic.AtomicReference;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
+import org.mockito.ArgumentCaptor;
 import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
 import org.mockito.Spy;
@@ -29,9 +34,16 @@ import org.mockito.stubbing.Answer;
 import org.robolectric.RobolectricTestRunner;
 import org.robolectric.RuntimeEnvironment;
 import org.robolectric.annotation.Config;
+import org.robolectric.annotation.Implementation;
+import org.robolectric.annotation.Implements;
 
-@Config(manifest = Config.NONE)
+// TODO(xster): we have 2 versions of robolectric Android shadows in
+// shell/platform/android/embedding_bundle/build.gradle. Remove the older
+// org.robolectric:android-all:4.1.2_r1-robolectric-r1 which doesn't have the right shadow
+// behaviors.
+@Config(manifest = Config.NONE, sdk = 27)
 @RunWith(RobolectricTestRunner.class)
+@TargetApi(27)
 public class FlutterViewTest {
   @Mock FlutterJNI mockFlutterJni;
   @Mock FlutterLoader mockFlutterLoader;
@@ -188,4 +200,97 @@ public class FlutterViewTest {
     // Verify results.
     assertEquals(SettingsChannel.PlatformBrightness.dark, reportedBrightness.get());
   }
+
+  @Test
+  @Config(
+      shadows = {
+        FlutterViewTest.ShadowFullscreenView.class,
+        FlutterViewTest.ShadowFullscreenViewGroup.class
+      })
+  public void setPaddingTopToZeroForFullscreenMode() {
+    FlutterView flutterView = new FlutterView(RuntimeEnvironment.application);
+    FlutterEngine flutterEngine =
+        spy(new FlutterEngine(RuntimeEnvironment.application, mockFlutterLoader, mockFlutterJni));
+    FlutterRenderer flutterRenderer = spy(new FlutterRenderer(mockFlutterJni));
+    when(flutterEngine.getRenderer()).thenReturn(flutterRenderer);
+
+    // When we attach a new FlutterView to the engine without any system insets, the viewport
+    // metrics
+    // default to 0.
+    flutterView.attachToFlutterEngine(flutterEngine);
+    ArgumentCaptor<FlutterRenderer.ViewportMetrics> viewportMetricsCaptor =
+        ArgumentCaptor.forClass(FlutterRenderer.ViewportMetrics.class);
+    verify(flutterRenderer).setViewportMetrics(viewportMetricsCaptor.capture());
+    assertEquals(0, viewportMetricsCaptor.getValue().paddingTop);
+
+    // Then we simulate the system applying a window inset.
+    WindowInsets windowInsets = mock(WindowInsets.class);
+    when(windowInsets.getSystemWindowInsetTop()).thenReturn(100);
+    when(windowInsets.getSystemWindowInsetBottom()).thenReturn(100);
+    when(windowInsets.getSystemWindowInsetLeft()).thenReturn(100);
+    when(windowInsets.getSystemWindowInsetRight()).thenReturn(100);
+    flutterView.onApplyWindowInsets(windowInsets);
+
+    // Verify.
+    verify(flutterRenderer, times(2)).setViewportMetrics(viewportMetricsCaptor.capture());
+    assertEquals(0, viewportMetricsCaptor.getValue().paddingTop);
+    // Padding bottom is always 0.
+    assertEquals(0, viewportMetricsCaptor.getValue().paddingBottom);
+    assertEquals(100, viewportMetricsCaptor.getValue().paddingLeft);
+    assertEquals(100, viewportMetricsCaptor.getValue().paddingRight);
+  }
+
+  @Test
+  public void reportSystemInsetWhenNotFullscreen() {
+    // Without custom shadows, the default system ui visibility flags is 0.
+    FlutterView flutterView = new FlutterView(RuntimeEnvironment.application);
+    assertEquals(0, flutterView.getSystemUiVisibility());
+
+    FlutterEngine flutterEngine =
+        spy(new FlutterEngine(RuntimeEnvironment.application, mockFlutterLoader, mockFlutterJni));
+    FlutterRenderer flutterRenderer = spy(new FlutterRenderer(mockFlutterJni));
+    when(flutterEngine.getRenderer()).thenReturn(flutterRenderer);
+
+    // When we attach a new FlutterView to the engine without any system insets, the viewport
+    // metrics
+    // default to 0.
+    flutterView.attachToFlutterEngine(flutterEngine);
+    ArgumentCaptor<FlutterRenderer.ViewportMetrics> viewportMetricsCaptor =
+        ArgumentCaptor.forClass(FlutterRenderer.ViewportMetrics.class);
+    verify(flutterRenderer).setViewportMetrics(viewportMetricsCaptor.capture());
+    assertEquals(0, viewportMetricsCaptor.getValue().paddingTop);
+
+    // Then we simulate the system applying a window inset.
+    WindowInsets windowInsets = mock(WindowInsets.class);
+    when(windowInsets.getSystemWindowInsetTop()).thenReturn(100);
+    when(windowInsets.getSystemWindowInsetBottom()).thenReturn(100);
+    when(windowInsets.getSystemWindowInsetLeft()).thenReturn(100);
+    when(windowInsets.getSystemWindowInsetRight()).thenReturn(100);
+    flutterView.onApplyWindowInsets(windowInsets);
+
+    // Verify.
+    verify(flutterRenderer, times(2)).setViewportMetrics(viewportMetricsCaptor.capture());
+    // Top padding is reported as-is.
+    assertEquals(100, viewportMetricsCaptor.getValue().paddingTop);
+    // Padding bottom is always 0.
+    assertEquals(0, viewportMetricsCaptor.getValue().paddingBottom);
+    assertEquals(100, viewportMetricsCaptor.getValue().paddingLeft);
+    assertEquals(100, viewportMetricsCaptor.getValue().paddingRight);
+  }
+
+  /*
+   * A custom shadow that reports fullscreen flag for system UI visibility
+   */
+  @Implements(View.class)
+  public static class ShadowFullscreenView {
+    @Implementation
+    public int getWindowSystemUiVisibility() {
+      return View.SYSTEM_UI_FLAG_FULLSCREEN;
+    }
+  }
+
+  // ViewGroup is the first shadow in the type hierarchy for FlutterView. Shadows need to mimic
+  // production classes' view hierarchy.
+  @Implements(ViewGroup.class)
+  public static class ShadowFullscreenViewGroup extends ShadowFullscreenView {}
 }