Provide lookup key to access Flutter assets in the APK (#4785)

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

@@ -9,6 +9,7 @@ import android.content.Context;
 import android.content.Intent;
 import android.util.Log;
 import io.flutter.plugin.common.*;
+import io.flutter.view.FlutterMain;
 import io.flutter.view.FlutterNativeView;
 import io.flutter.view.FlutterView;
 import io.flutter.view.TextureRegistry;
@@ -111,6 +112,16 @@ public class FlutterPluginRegistry
             return mFlutterView;
         }
 
+        @Override
+        public String lookupKeyForAsset(String asset) {
+            return FlutterMain.getLookupKeyForAsset(asset);
+        }
+
+        @Override
+        public String lookupKeyForAsset(String asset, String packageName) {
+            return FlutterMain.getLookupKeyForAsset(asset, packageName);
+        }
+
         @Override
         public Registrar publish(Object value) {
             mPluginMap.put(pluginKey, value);

shell/platform/android/io/flutter/plugin/common/PluginRegistry.java

@@ -105,6 +105,29 @@ public interface PluginRegistry {
          */
         FlutterView view();
 
+
+        /**
+         * Returns the file name for the given asset.
+         * The returned file name can be used to access the asset in the APK
+         * through the {@link AssetManager} API.
+         *
+         * @param asset the name of the asset. The name can be hierarchical
+         * @return      the filename to be used with {@link AssetManager}
+         */
+        String lookupKeyForAsset(String asset);
+
+        /**
+         * Returns the file name for the given asset which originates from the
+         * specified packageName. The returned file name can be used to access
+         * the asset in the APK through the {@link AssetManager} API.
+         *
+         * @param asset       the name of the asset. The name can be hierarchical
+         * @param packageName the name of the package from which the asset originates
+         * @return            the file name to be used with {@link AssetManager}
+         */
+        String lookupKeyForAsset(String asset, String packageName);
+
+
         /**
          * Publishes a value associated with the plugin being registered.
          *

shell/platform/android/io/flutter/view/FlutterMain.java

@@ -73,7 +73,7 @@ public class FlutterMain {
     private static final String MANIFEST = "flutter.yaml";
 
     private static String fromFlutterAssets(String filePath) {
-        return sFlutterAssetsDir + "/" + filePath;
+        return sFlutterAssetsDir + File.separator + filePath;
     }
 
     private static final Set<String> SKY_RESOURCES = ImmutableSetBuilder.<String>newInstance()
@@ -308,4 +308,30 @@ public class FlutterMain {
         File appBundle = new File(dataDirectory, sFlutterAssetsDir);
         return appBundle.exists() ? appBundle.getPath() : null;
     }
+
+    /**
+     * Returns the file name for the given asset.
+     * The returned file name can be used to access the asset in the APK
+     * through the {@link AssetManager} API.
+     *
+     * @param asset the name of the asset. The name can be hierarchical
+     * @return      the filename to be used with {@link AssetManager}
+     */
+    public static String getLookupKeyForAsset(String asset) {
+        return fromFlutterAssets(asset);
+    }
+
+    /**
+     * Returns the file name for the given asset which originates from the
+     * specified packageName. The returned file name can be used to access
+     * the asset in the APK through the {@link AssetManager} API.
+     *
+     * @param asset       the name of the asset. The name can be hierarchical
+     * @param packageName the name of the package from which the asset originates
+     * @return            the file name to be used with {@link AssetManager}
+     */
+    public static String getLookupKeyForAsset(String asset, String packageName) {
+        return getLookupKeyForAsset(
+            "packages" + File.separator + packageName + File.separator + asset);
+    }
 }

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

@@ -254,6 +254,14 @@ public class FlutterView extends SurfaceView
         return mNativeView.getPluginRegistry();
     }
 
+    public String getLookupKeyForAsset(String asset) {
+        return FlutterMain.getLookupKeyForAsset(asset);
+    }
+
+    public String getLookupKeyForAsset(String asset, String packageName) {
+        return FlutterMain.getLookupKeyForAsset(asset, packageName);
+    }
+
     public void addActivityLifecycleListener(ActivityLifecycleListener listener) {
         mActivityLifecycleListeners.add(listener);
     }