[jni] Add support for JArray.of() (#1938)

Author: brianquinlan

pkgs/jni/CHANGELOG.md

@@ -7,6 +7,8 @@
   java types.
 - Do not require a `dylibDir` when running `Jni.spawn` from Dart standalone,
   instead use the default value of `build/jni_libs`.
+- Added `JArray.of`, which allows a `JArray` to be constructed from an
+  `Iterable`.
 
 ## 0.13.0
 

pkgs/jni/lib/src/jarray.dart

@@ -125,9 +125,12 @@ class JArray<E extends JObject?> extends JObject with Iterable<E> {
   factory JArray(JObjType<E> elementType, int length) {
     RangeError.checkNotNegative(length);
     if (!elementType.isNullable) {
-      throw StateError('Element type of JArray must be nullable when '
-          'all elements with null\n\n'
-          'Try using .nullableType instead');
+      throw ArgumentError.value(
+          elementType,
+          'elementType',
+          'Element type of JArray must be nullable when constructed with a '
+              'length (because the elements will be initialized to null).\n\n'
+              'Try using .nullableType instead');
     }
     return _newArray<E>(elementType, length);
   }
@@ -159,6 +162,13 @@ class JArray<E extends JObject?> extends JObject with Iterable<E> {
     return _newArray<$E>(E, length, fill);
   }
 
+  /// Creates a [JArray] from `elements`.
+  static JArray<$E> of<$E extends JObject?>(
+      JObjType<$E> elementType, Iterable<$E> elements) {
+    return _newArray<$E>(elementType, elements.length)
+      ..setRange(0, elements.length, elements);
+  }
+
   /// The number of elements in this array.
   @override
   late final length = Jni.env.GetArrayLength(reference.pointer);

pkgs/jni/test/jarray_test.dart

@@ -411,6 +411,8 @@ void run({required TestRunnerCallback testRunner}) {
       expect(array[0], isNull);
       expect(array[1], isNull);
       expect(array[2], isNull);
+
+      expect(() => JArray(JObject.type, 3), throwsArgumentError);
     });
   });
   testRunner('Java 2d array', () {
@@ -447,6 +449,34 @@ void run({required TestRunnerCallback testRunner}) {
       expect(array[2].toDartString(releaseOriginal: true), 'abc');
     });
   });
+  testRunner('JArray.of', () {
+    using((arena) {
+      final array1 = JArray.of(JString.type, [
+        'apple'.toJString()..releasedBy(arena),
+        'banana'.toJString()..releasedBy(arena)
+      ])
+        ..releasedBy(arena);
+      expect(array1.length, 2);
+      expect(array1[0].toDartString(releaseOriginal: true), 'apple');
+      expect(array1[1].toDartString(releaseOriginal: true), 'banana');
+
+      final array2 = JArray.of(JString.nullableType, [
+        'apple'.toJString()..releasedBy(arena),
+        null,
+        'banana'.toJString()..releasedBy(arena)
+      ]);
+      expect(array2.length, 3);
+      expect(array2[0]!.toDartString(releaseOriginal: true), 'apple');
+      expect(array2[1], isNull);
+      expect(array2[2]!.toDartString(releaseOriginal: true), 'banana');
+
+      final array3 = JArray.of<JObject>(JString.type, []);
+      expect(array3.length, 0);
+
+      final array4 = JArray.of<JObject?>(JString.nullableType, []);
+      expect(array4.length, 0);
+    });
+  });
   testRunner('JArray of JByte', () {
     using((arena) {
       final arr = JArray(JByte.nullableType, 1)..releasedBy(arena);