Revert "Bump everything to Android 21"

shell/platform/android/AndroidManifest.xml

@@ -5,7 +5,7 @@
  -->
 <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="io.flutter.app" android:versionCode="1" android:versionName="0.0.1">
 
-    <uses-sdk android:minSdkVersion="21" android:targetSdkVersion="34" />
+    <uses-sdk android:minSdkVersion="16" android:targetSdkVersion="34" />
     <uses-permission android:name="android.permission.INTERNET" />
     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
     <uses-feature android:name="android.hardware.sensor.accelerometer" android:required="true" />

shell/platform/android/build.gradle

@@ -23,7 +23,7 @@ android {
     compileSdkVersion 34
 
     defaultConfig {
-        minSdkVersion 21
+        minSdkVersion 19
     }
 
     sourceSets {

shell/platform/android/io/flutter/app/FlutterActivityDelegate.java

@@ -17,6 +17,7 @@
 import android.content.res.Configuration;
 import android.content.res.Resources.NotFoundException;
 import android.graphics.drawable.Drawable;
+import android.os.Build;
 import android.os.Bundle;
 import android.util.TypedValue;
 import android.view.View;
@@ -136,10 +137,12 @@ public boolean onActivityResult(int requestCode, int resultCode, Intent data) {
 
   @Override
   public void onCreate(Bundle savedInstanceState) {
-    Window window = activity.getWindow();
-    window.addFlags(LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
-    window.setStatusBarColor(0x40000000);
-    window.getDecorView().setSystemUiVisibility(PlatformPlugin.DEFAULT_SYSTEM_UI);
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
+      Window window = activity.getWindow();
+      window.addFlags(LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
+      window.setStatusBarColor(0x40000000);
+      window.getDecorView().setSystemUiVisibility(PlatformPlugin.DEFAULT_SYSTEM_UI);
+    }
 
     String[] args = getArgsFromIntent(activity.getIntent());
     FlutterMain.ensureInitializationComplete(activity.getApplicationContext(), args);

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

@@ -204,7 +204,9 @@ public boolean onTouchEvent(@NonNull MotionEvent event, @NonNull Matrix transfor
   public boolean onGenericMotionEvent(@NonNull MotionEvent event, @NonNull Context context) {
     // Method isFromSource is only available in API 18+ (Jelly Bean MR2)
     // Mouse hover support is not implemented for API < 18.
-    boolean isPointerEvent = event.isFromSource(InputDevice.SOURCE_CLASS_POINTER);
+    boolean isPointerEvent =
+        Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR2
+            && event.isFromSource(InputDevice.SOURCE_CLASS_POINTER);
     boolean isMovementEvent =
         (event.getActionMasked() == MotionEvent.ACTION_HOVER_MOVE
             || event.getActionMasked() == MotionEvent.ACTION_SCROLL);

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

@@ -49,6 +49,7 @@
 import io.flutter.embedding.engine.plugins.activity.ActivityControlSurface;
 import io.flutter.embedding.engine.plugins.util.GeneratedPluginRegister;
 import io.flutter.plugin.platform.PlatformPlugin;
+import io.flutter.util.ViewUtils;
 import java.util.ArrayList;
 import java.util.List;
 
@@ -215,7 +216,7 @@ public class FlutterActivity extends Activity
    * <p>This ID can be used to lookup {@code FlutterView} in the Android view hierarchy. For more,
    * see {@link android.view.View#findViewById}.
    */
-  public static final int FLUTTER_VIEW_ID = View.generateViewId();
+  public static final int FLUTTER_VIEW_ID = ViewUtils.generateViewId(0xF1F2);
 
   /**
    * Creates an {@link Intent} that launches a {@code FlutterActivity}, which creates a {@link
@@ -772,10 +773,12 @@ private View createFlutterView() {
   }
 
   private void configureStatusBarForFullscreenFlutterExperience() {
-    Window window = getWindow();
-    window.addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
-    window.setStatusBarColor(0x40000000);
-    window.getDecorView().setSystemUiVisibility(PlatformPlugin.DEFAULT_SYSTEM_UI);
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
+      Window window = getWindow();
+      window.addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
+      window.setStatusBarColor(0x40000000);
+      window.getDecorView().setSystemUiVisibility(PlatformPlugin.DEFAULT_SYSTEM_UI);
+    }
   }
 
   @Override

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

@@ -8,6 +8,7 @@
 import android.content.ComponentCallbacks2;
 import android.content.Context;
 import android.content.Intent;
+import android.os.Build;
 import android.os.Bundle;
 import android.view.LayoutInflater;
 import android.view.View;
@@ -16,6 +17,7 @@
 import androidx.activity.OnBackPressedCallback;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
+import androidx.annotation.RequiresApi;
 import androidx.annotation.VisibleForTesting;
 import androidx.fragment.app.Fragment;
 import androidx.fragment.app.FragmentActivity;
@@ -25,6 +27,7 @@
 import io.flutter.embedding.engine.FlutterShellArgs;
 import io.flutter.embedding.engine.renderer.FlutterUiDisplayListener;
 import io.flutter.plugin.platform.PlatformPlugin;
+import io.flutter.util.ViewUtils;
 import java.util.ArrayList;
 import java.util.List;
 
@@ -104,7 +107,7 @@ public class FlutterFragment extends Fragment
    * <p>This ID can be used to lookup {@code FlutterView} in the Android view hierarchy. For more,
    * see {@link android.view.View#findViewById}.
    */
-  public static final int FLUTTER_VIEW_ID = View.generateViewId();
+  public static final int FLUTTER_VIEW_ID = ViewUtils.generateViewId(0xF1F2);
 
   private static final String TAG = "FlutterFragment";
 
@@ -167,15 +170,18 @@ public class FlutterFragment extends Fragment
   protected static final String ARG_SHOULD_AUTOMATICALLY_HANDLE_ON_BACK_PRESSED =
       "should_automatically_handle_on_back_pressed";
 
+  @RequiresApi(18)
   private final OnWindowFocusChangeListener onWindowFocusChangeListener =
-      new OnWindowFocusChangeListener() {
-        @Override
-        public void onWindowFocusChanged(boolean hasFocus) {
-          if (stillAttachedForEvent("onWindowFocusChanged")) {
-            delegate.onWindowFocusChanged(hasFocus);
+      Build.VERSION.SDK_INT >= 18
+          ? new OnWindowFocusChangeListener() {
+            @Override
+            public void onWindowFocusChanged(boolean hasFocus) {
+              if (stillAttachedForEvent("onWindowFocusChanged")) {
+                delegate.onWindowFocusChanged(hasFocus);
+              }
+            }
           }
-        }
-      };
+          : null;
 
   /**
    * Creates a {@code FlutterFragment} with a default configuration.
@@ -1122,15 +1128,20 @@ public void onStop() {
   @Override
   public void onViewCreated(View view, Bundle savedInstanceState) {
     super.onViewCreated(view, savedInstanceState);
-    view.getViewTreeObserver().addOnWindowFocusChangeListener(onWindowFocusChangeListener);
+    if (Build.VERSION.SDK_INT >= 18) {
+      view.getViewTreeObserver().addOnWindowFocusChangeListener(onWindowFocusChangeListener);
+    }
   }
 
   @Override
   public void onDestroyView() {
     super.onDestroyView();
-    requireView()
-        .getViewTreeObserver()
-        .removeOnWindowFocusChangeListener(onWindowFocusChangeListener);
+    if (Build.VERSION.SDK_INT >= 18) {
+      // onWindowFocusChangeListener is API 18+ only.
+      requireView()
+          .getViewTreeObserver()
+          .removeOnWindowFocusChangeListener(onWindowFocusChangeListener);
+    }
     if (stillAttachedForEvent("onDestroyView")) {
       delegate.onDestroyView();
     }

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

@@ -27,6 +27,7 @@
 import android.content.pm.PackageManager;
 import android.graphics.Color;
 import android.graphics.drawable.ColorDrawable;
+import android.os.Build;
 import android.os.Bundle;
 import android.view.View;
 import android.view.ViewGroup;
@@ -44,6 +45,7 @@
 import io.flutter.embedding.engine.FlutterShellArgs;
 import io.flutter.embedding.engine.plugins.util.GeneratedPluginRegister;
 import io.flutter.plugin.platform.PlatformPlugin;
+import io.flutter.util.ViewUtils;
 import java.util.ArrayList;
 import java.util.List;
 
@@ -65,7 +67,8 @@ public class FlutterFragmentActivity extends FragmentActivity
   // FlutterFragment management.
   private static final String TAG_FLUTTER_FRAGMENT = "flutter_fragment";
   // TODO(mattcarroll): replace ID with R.id when build system supports R.java
-  public static final int FRAGMENT_CONTAINER_ID = View.generateViewId();
+  public static final int FRAGMENT_CONTAINER_ID =
+      ViewUtils.generateViewId(609893468); // random number
 
   /**
    * Creates an {@link Intent} that launches a {@code FlutterFragmentActivity}, which executes a
@@ -597,10 +600,12 @@ protected FlutterFragment createFlutterFragment() {
   }
 
   private void configureStatusBarForFullscreenFlutterExperience() {
-    Window window = getWindow();
-    window.addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
-    window.setStatusBarColor(0x40000000);
-    window.getDecorView().setSystemUiVisibility(PlatformPlugin.DEFAULT_SYSTEM_UI);
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
+      Window window = getWindow();
+      window.addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
+      window.setStatusBarColor(0x40000000);
+      window.getDecorView().setSystemUiVisibility(PlatformPlugin.DEFAULT_SYSTEM_UI);
+    }
   }
 
   @Override

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

@@ -39,6 +39,7 @@
  * an {@link android.media.Image} and renders it to the {@link android.graphics.Canvas} in {@code
  * onDraw}.
  */
+@TargetApi(19)
 public class FlutterImageView extends View implements RenderSurface {
   private static final String TAG = "FlutterImageView";
 
@@ -98,6 +99,7 @@ private static void logW(String format, Object... args) {
     Log.w(TAG, String.format(Locale.US, format, args));
   }
 
+  @TargetApi(19)
   @SuppressLint("WrongConstant") // RGBA_8888 is a valid constant.
   @NonNull
   private static ImageReader createImageReader(int width, int height) {
@@ -185,6 +187,7 @@ public void resume() {
    * Acquires the next image to be drawn to the {@link android.graphics.Canvas}. Returns true if
    * there's an image available in the queue.
    */
+  @TargetApi(19)
   public boolean acquireLatestImage() {
     if (!isAttachedToFlutterRenderer) {
       return false;

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

@@ -290,6 +290,7 @@ public FlutterView(@NonNull Context context, @NonNull FlutterTextureView flutter
    * <p>{@code FlutterView} requires an {@code Activity} instead of a generic {@code Context} to be
    * compatible with {@link PlatformViewsController}.
    */
+  @TargetApi(19)
   public FlutterView(@NonNull Context context, @NonNull FlutterImageView flutterImageView) {
     this(context, null, flutterImageView);
   }
@@ -356,6 +357,7 @@ private FlutterView(
     init();
   }
 
+  @TargetApi(19)
   private FlutterView(
       @NonNull Context context,
       @Nullable AttributeSet attrs,
@@ -641,7 +643,8 @@ else if (rotation == Surface.ROTATION_0 || rotation == Surface.ROTATION_180) {
   //
   // This method is replaced by Android API 30 (R/11) getInsets() method which can take the
   // android.view.WindowInsets.Type.ime() flag to find the keyboard inset.
-
+  @TargetApi(20)
+  @RequiresApi(20)
   private int guessBottomKeyboardInset(WindowInsets insets) {
     int screenHeight = getRootView().getHeight();
     // Magic number due to this being a heuristic. This should be replaced, but we have not
@@ -667,7 +670,8 @@ private int guessBottomKeyboardInset(WindowInsets insets) {
    * wider than expected padding when the status and navigation bars are hidden.
    */
   @Override
-
+  @TargetApi(20)
+  @RequiresApi(20)
   // The annotations to suppress "InlinedApi" and "NewApi" lints prevent lint warnings
   // caused by usage of Android Q APIs. These calls are safe because they are
   // guarded.
@@ -798,6 +802,53 @@ navigationBarVisible && guessBottomKeyboardInset(insets) == 0
     sendViewportMetricsToFlutter();
     return newInsets;
   }
+
+  /**
+   * Invoked when Android's desired window insets change, i.e., padding.
+   *
+   * <p>{@code fitSystemWindows} is an earlier version of {@link
+   * #onApplyWindowInsets(WindowInsets)}. See that method for more details about how window insets
+   * relate to Flutter.
+   */
+  @Override
+  @SuppressWarnings("deprecation")
+  protected boolean fitSystemWindows(@NonNull Rect insets) {
+    if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.KITKAT) {
+      // Status bar, left/right system insets partially obscure content (padding).
+      viewportMetrics.viewPaddingTop = insets.top;
+      viewportMetrics.viewPaddingRight = insets.right;
+      viewportMetrics.viewPaddingBottom = 0;
+      viewportMetrics.viewPaddingLeft = insets.left;
+
+      // Bottom system inset (keyboard) should adjust scrollable bottom edge (inset).
+      viewportMetrics.viewInsetTop = 0;
+      viewportMetrics.viewInsetRight = 0;
+      viewportMetrics.viewInsetBottom = insets.bottom;
+      viewportMetrics.viewInsetLeft = 0;
+
+      Log.v(
+          TAG,
+          "Updating window insets (fitSystemWindows()):\n"
+              + "Status bar insets: Top: "
+              + viewportMetrics.viewPaddingTop
+              + ", Left: "
+              + viewportMetrics.viewPaddingLeft
+              + ", Right: "
+              + viewportMetrics.viewPaddingRight
+              + "\n"
+              + "Keyboard insets: Bottom: "
+              + viewportMetrics.viewInsetBottom
+              + ", Left: "
+              + viewportMetrics.viewInsetLeft
+              + ", Right: "
+              + viewportMetrics.viewInsetRight);
+
+      sendViewportMetricsToFlutter();
+      return true;
+    } else {
+      return super.fitSystemWindows(insets);
+    }
+  }
   // ------- End: Process View configuration that Flutter cares about. --------
 
   // -------- Start: Process UI I/O that Flutter cares about. -------
@@ -879,7 +930,14 @@ public boolean onTouchEvent(@NonNull MotionEvent event) {
       return super.onTouchEvent(event);
     }
 
-    requestUnbufferedDispatch(event);
+    // TODO(abarth): This version check might not be effective in some
+    // versions of Android that statically compile code and will be upset
+    // at the lack of |requestUnbufferedDispatch|. Instead, we should factor
+    // version-dependent code into separate classes for each supported
+    // version and dispatch dynamically.
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
+      requestUnbufferedDispatch(event);
+    }
 
     return androidTouchProcessor.onTouchEvent(event);
   }

shell/platform/android/io/flutter/embedding/engine/FlutterJNI.java

@@ -1297,17 +1297,22 @@ public String[] computePlatformResolvedLocale(@NonNull String[] strings) {
       String countryCode = strings[i + 1];
       String scriptCode = strings[i + 2];
       // Convert to Locales via LocaleBuilder if available (API 21+) to include scriptCode.
-      Locale.Builder localeBuilder = new Locale.Builder();
-      if (!languageCode.isEmpty()) {
-        localeBuilder.setLanguage(languageCode);
-      }
-      if (!countryCode.isEmpty()) {
-        localeBuilder.setRegion(countryCode);
-      }
-      if (!scriptCode.isEmpty()) {
-        localeBuilder.setScript(scriptCode);
+      if (Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.LOLLIPOP) {
+        Locale.Builder localeBuilder = new Locale.Builder();
+        if (!languageCode.isEmpty()) {
+          localeBuilder.setLanguage(languageCode);
+        }
+        if (!countryCode.isEmpty()) {
+          localeBuilder.setRegion(countryCode);
+        }
+        if (!scriptCode.isEmpty()) {
+          localeBuilder.setScript(scriptCode);
+        }
+        supportedLocales.add(localeBuilder.build());
+      } else {
+        // Pre-API 21, we fall back on scriptCode-less locales.
+        supportedLocales.add(new Locale(languageCode, countryCode));
       }
-      supportedLocales.add(localeBuilder.build());
     }
 
     Locale result = localizationPlugin.resolveNativeLocale(supportedLocales);
@@ -1318,7 +1323,11 @@ public String[] computePlatformResolvedLocale(@NonNull String[] strings) {
     String[] output = new String[localeDataLength];
     output[0] = result.getLanguage();
     output[1] = result.getCountry();
-    output[2] = result.getScript();
+    if (Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.LOLLIPOP) {
+      output[2] = result.getScript();
+    } else {
+      output[2] = "";
+    }
     return output;
   }