I do have a solution and it works with barebone code provided in the Flutter-Desktop-Embedding project which I assume you used for your desktop application. You are on the right track but just need some finalisation.
For testing, I used this simple c code with several functions to test passing the pointers, returning pointers, filling memory, allocation and deallocation.
This is the C code I used in my dll.
#define WIN32_LEAN_AND_MEAN
#include <Windows.h>
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
__declspec(dllexport) uint8_t* createarray(int32_t size) {
uint8_t* arr = malloc(size);
return arr;
}
__declspec(dllexport) void populatearray(uint8_t* arr,uint32_t size){
for (uint32_t index = 0; index < size; ++index) {
arr[index] = index & 0xff;
}
}
__declspec(dllexport) void destroyarray(uint8_t* arr) {
free(arr);
}
createarray allocates a uint8_t pointer with given size and returns it to the caller.
populatearray takes the uint8_t pointer argument along with size and populates it with index
destroyarray simply frees the allocated memory.
Now for the boilerplate flutter code.
This is the default code provided for main.dart in Flutter-Desktop-Embedding project which I cloned from here https://github.com/google/flutter-desktop-embedding.git (I assume you've done this step already)
// Copyright 2018 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
import 'dart:io' show Platform;
import 'dart:math' as math;
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:menubar/menubar.dart';
import 'package:window_size/window_size.dart' as window_size;
import 'keyboard_test_page.dart';
void main() {
// Try to resize and reposition the window to be half the width and height
// of its screen, centered horizontally and shifted up from center.
WidgetsFlutterBinding.ensureInitialized();
window_size.getWindowInfo().then((window) {
final screen = window.screen;
if (screen != null) {
final screenFrame = screen.visibleFrame;
final width = math.max((screenFrame.width / 2).roundToDouble(), 800.0);
final height = math.max((screenFrame.height / 2).roundToDouble(), 600.0);
final left = ((screenFrame.width - width) / 2).roundToDouble();
final top = ((screenFrame.height - height) / 3).roundToDouble();
final frame = Rect.fromLTWH(left, top, width, height);
window_size.setWindowFrame(frame);
window_size.setWindowMinSize(Size(0.8 * width, 0.8 * height));
window_size.setWindowMaxSize(Size(1.5 * width, 1.5 * height));
window_size
.setWindowTitle('Flutter Testbed on ${Platform.operatingSystem}');
}
});
runApp(new MyApp());
}
/// Top level widget for the application.
class MyApp extends StatefulWidget {
/// Constructs a new app with the given [key].
const MyApp({Key? key}) : super(key: key);
@override
_AppState createState() => new _AppState();
}
class _AppState extends State<MyApp> {
Color _primaryColor = Colors.blue;
int _counter = 0;
static _AppState? of(BuildContext context) =>
context.findAncestorStateOfType<_AppState>();
/// Sets the primary color of the app.
void setPrimaryColor(Color color) {
setState(() {
_primaryColor = color;
});
}
void incrementCounter() {
_setCounter(_counter + 1);
}
void _decrementCounter() {
_setCounter(_counter - 1);
}
void _setCounter(int value) {
setState(() {
_counter = value;
});
}
/// Rebuilds the native menu bar based on the current state.
void updateMenubar() {
setApplicationMenu([
Submenu(label: 'Color', children: [
MenuItem(
label: 'Reset',
enabled: _primaryColor != Colors.blue,
shortcut: LogicalKeySet(
LogicalKeyboardKey.meta, LogicalKeyboardKey.backspace),
onClicked: () {
setPrimaryColor(Colors.blue);
}),
MenuDivider(),
Submenu(label: 'Presets', children: [
MenuItem(
label: 'Red',
enabled: _primaryColor != Colors.red,
shortcut: LogicalKeySet(LogicalKeyboardKey.meta,
LogicalKeyboardKey.shift, LogicalKeyboardKey.keyR),
onClicked: () {
setPrimaryColor(Colors.red);
}),
MenuItem(
label: 'Green',
enabled: _primaryColor != Colors.green,
shortcut: LogicalKeySet(LogicalKeyboardKey.meta,
LogicalKeyboardKey.alt, LogicalKeyboardKey.keyG),
onClicked: () {
setPrimaryColor(Colors.green);
}),
MenuItem(
label: 'Purple',
enabled: _primaryColor != Colors.deepPurple,
shortcut: LogicalKeySet(LogicalKeyboardKey.meta,
LogicalKeyboardKey.control, LogicalKeyboardKey.keyP),
onClicked: () {
setPrimaryColor(Colors.deepPurple);
}),
])
]),
Submenu(label: 'Counter', children: [
MenuItem(
label: 'Reset',
enabled: _counter != 0,
shortcut: LogicalKeySet(
LogicalKeyboardKey.meta, LogicalKeyboardKey.digit0),
onClicked: () {
_setCounter(0);
}),
MenuDivider(),
MenuItem(
label: 'Increment',
shortcut: LogicalKeySet(LogicalKeyboardKey.f2),
onClicked: incrementCounter),
MenuItem(
label: 'Decrement',
enabled: _counter > 0,
shortcut: LogicalKeySet(LogicalKeyboardKey.f1),
onClicked: _decrementCounter),
]),
]);
}
@override
Widget build(BuildContext context) {
// Any time the state changes, the menu needs to be rebuilt.
updateMenubar();
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
primaryColor: _primaryColor,
accentColor: _primaryColor,
),
darkTheme: ThemeData.dark(),
home: _MyHomePage(title: 'Flutter Demo Home Page', counter: _counter),
);
}
}
class _MyHomePage extends StatelessWidget {
const _MyHomePage({required this.title, this.counter = 0});
final String title;
final int counter;
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(title),
),
body: LayoutBuilder(
builder: (context, viewportConstraints) {
return SingleChildScrollView(
child: ConstrainedBox(
constraints:
BoxConstraints(minHeight: viewportConstraints.maxHeight),
child: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
const Text(
'You have pushed the button this many times:',
),
new Text(
'$counter',
style: Theme.of(context).textTheme.headline4,
),
TextInputTestWidget(),
new ElevatedButton(
child: new Text('Test raw keyboard events'),
onPressed: () {
Navigator.of(context).push(new MaterialPageRoute(
builder: (context) => KeyboardTestPage()));
},
),
Padding(
padding: const EdgeInsets.all(8.0),
child: Container(
width: 380.0,
height: 100.0,
decoration: BoxDecoration(
border: Border.all(color: Colors.grey, width: 1.0)),
child: Scrollbar(
child: ListView.builder(
padding: EdgeInsets.all(8.0),
itemExtent: 20.0,
itemCount: 50,
itemBuilder: (context, index) {
return Text('entry $index');
},
),
),
),
),
],
),
),
),
);
},
),
floatingActionButton: FloatingActionButton(
onPressed: _AppState.of(context)!.incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
}
/// A widget containing controls to test text input.
class TextInputTestWidget extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Row(
mainAxisAlignment: MainAxisAlignment.center,
children: const <Widget>[
SampleTextField(),
SampleTextField(),
],
);
}
}
/// A text field with styling suitable for including in a TextInputTestWidget.
class SampleTextField extends StatelessWidget {
/// Creates a new sample text field.
const SampleTextField();
@override
Widget build(BuildContext context) {
return Container(
width: 200.0,
padding: const EdgeInsets.all(10.0),
child: TextField(
decoration: InputDecoration(border: OutlineInputBorder()),
),
);
}
}
Now for our portion of the code, we have to create a function pointer for each function we want to call in the dll, we need the function name properly and the propper/correct number of arguments.
We will need the dart:io and dart:ffi packages. dart:io is already in the code, just need to import dart:ffi
import 'dart:ffi'; // For FFI
Now to create a handle to the library which needs to be loaded, DynamicLibrary.open needs to be called with the name of the dll. (The dll needs to be placed in the execution path of the dart application or an absolute path needs to be given. The execution path is build/windows/runner/Debug)
final DynamicLibrary nativePointerTestLib = DynamicLibrary.open("dynamicloadtest.dll");
My handle is called nativePointerTestLib and the name of the dll is "dynamicloadtest.dll" (Yes I should probably use better naming conventions)
Next, each function pointer needs to be created. There are three functions in the dll that I want to call : createarray, populatearray, destroyarray.
The first takes a size argument of int -> returns pointer to array (Pointer)
The second takes the pointer along with size -> void return
The third takes just the pointer -> void return
final Pointer<Uint8> Function(int size) nativeCreateArray =
nativePointerTestLib
.lookup<NativeFunction<Pointer<Uint8> Function(Int32)>>("createarray")
.asFunction();
final void Function(Pointer<Uint8> arr,int size) nativePopulateArray =
nativePointerTestLib
.lookup<NativeFunction<Void Function(Pointer<Uint8>, Int32)>>("populatearray")
.asFunction();
final void Function(Pointer<Uint8> arr) nativeDestroyArray =
nativePointerTestLib
.lookup<NativeFunction<Void Function(Pointer<Uint8>)>>("destroyarray")
.asFunction();
I named the function pointers nativeCreateArray, nativePopulateArray, nativeDestroyArray
Lastly it's just a matter of calling each function and testing to see if they worked. I just picked a random function in the boiler plate code, void _setCounter(int value) which sets the counter value and later gets displayed. I'm just going to add additional code to that method to execute our function calls as well as print the results to see if it worked.
old method
void _setCounter(int value) {
setState(() {
_counter = value;
});
}
new method with our function calls
void _setCounter(int value) {
setState(() {
Pointer<Uint8> parray = nativeCreateArray(5);
nativePopulateArray(parray,5);
//Now lets print
print(parray);
String str= "";
for(int i = 0 ; i < 5; ++i){
int val = parray.elementAt(i).value;
str+=val.toString() +" ";
}
print(str);
nativeDestroyArray(parray);
_counter = value;
});
}
I called nativeCreate with a size of 5. The dll will allocate 5 bytes for the array.
Next I call populate which will insert index 0 to 4 in each element of the array.
Then I loop through the array grabbing every element at that array index and then getting the value. I assign that value to a string and finally print and destroy the array.
Final code everything put together:
// Copyright 2018 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
import 'dart:io' show Platform;
import 'dart:math' as math;
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:menubar/menubar.dart';
import 'package:window_size/window_size.dart' as window_size;
import 'keyboard_test_page.dart';
import 'dart:ffi'; // For FFI
final DynamicLibrary nativePointerTestLib = DynamicLibrary.open("dynamicloadtest.dll");
final Pointer<Uint8> Function(int size) nativeCreateArray =
nativePointerTestLib
.lookup<NativeFunction<Pointer<Uint8> Function(Int32)>>("createarray")
.asFunction();
final void Function(Pointer<Uint8> arr,int size) nativePopulateArray =
nativePointerTestLib
.lookup<NativeFunction<Void Function(Pointer<Uint8>, Int32)>>("populatearray")
.asFunction();
final void Function(Pointer<Uint8> arr) nativeDestroyArray =
nativePointerTestLib
.lookup<NativeFunction<Void Function(Pointer<Uint8>)>>("destroyarray")
.asFunction();
void main() {
// Try to resize and reposition the window to be half the width and height
// of its screen, centered horizontally and shifted up from center.
WidgetsFlutterBinding.ensureInitialized();
window_size.getWindowInfo().then((window) {
final screen = window.screen;
if (screen != null) {
final screenFrame = screen.visibleFrame;
final width = math.max((screenFrame.width / 2).roundToDouble(), 800.0);
final height = math.max((screenFrame.height / 2).roundToDouble(), 600.0);
final left = ((screenFrame.width - width) / 2).roundToDouble();
final top = ((screenFrame.height - height) / 3).roundToDouble();
final frame = Rect.fromLTWH(left, top, width, height);
window_size.setWindowFrame(frame);
window_size.setWindowMinSize(Size(0.8 * width, 0.8 * height));
window_size.setWindowMaxSize(Size(1.5 * width, 1.5 * height));
window_size
.setWindowTitle('Flutter Testbed on ${Platform.operatingSystem}');
}
});
runApp(new MyApp());
}
/// Top level widget for the application.
class MyApp extends StatefulWidget {
/// Constructs a new app with the given [key].
const MyApp({Key? key}) : super(key: key);
@override
_AppState createState() => new _AppState();
}
class _AppState extends State<MyApp> {
Color _primaryColor = Colors.blue;
int _counter = 0;
static _AppState? of(BuildContext context) =>
context.findAncestorStateOfType<_AppState>();
/// Sets the primary color of the app.
void setPrimaryColor(Color color) {
setState(() {
_primaryColor = color;
});
}
void incrementCounter() {
_setCounter(_counter + 1);
}
void _decrementCounter() {
_setCounter(_counter - 1);
}
void _setCounter(int value) {
setState(() {
Pointer<Uint8> parray = nativeCreateArray(5);
nativePopulateArray(parray,5);
//Now lets print
print(parray);
String str= "";
for(int i = 0 ; i < 5; ++i){
int val = parray.elementAt(i).value;
str+=val.toString() +" ";
}
print(str);
nativeDestroyArray(parray);
_counter = value;
});
}
/// Rebuilds the native menu bar based on the current state.
void updateMenubar() {
setApplicationMenu([
Submenu(label: 'Color', children: [
MenuItem(
label: 'Reset',
enabled: _primaryColor != Colors.blue,
shortcut: LogicalKeySet(
LogicalKeyboardKey.meta, LogicalKeyboardKey.backspace),
onClicked: () {
setPrimaryColor(Colors.blue);
}),
MenuDivider(),
Submenu(label: 'Presets', children: [
MenuItem(
label: 'Red',
enabled: _primaryColor != Colors.red,
shortcut: LogicalKeySet(LogicalKeyboardKey.meta,
LogicalKeyboardKey.shift, LogicalKeyboardKey.keyR),
onClicked: () {
setPrimaryColor(Colors.red);
}),
MenuItem(
label: 'Green',
enabled: _primaryColor != Colors.green,
shortcut: LogicalKeySet(LogicalKeyboardKey.meta,
LogicalKeyboardKey.alt, LogicalKeyboardKey.keyG),
onClicked: () {
setPrimaryColor(Colors.green);
}),
MenuItem(
label: 'Purple',
enabled: _primaryColor != Colors.deepPurple,
shortcut: LogicalKeySet(LogicalKeyboardKey.meta,
LogicalKeyboardKey.control, LogicalKeyboardKey.keyP),
onClicked: () {
setPrimaryColor(Colors.deepPurple);
}),
])
]),
Submenu(label: 'Counter', children: [
MenuItem(
label: 'Reset',
enabled: _counter != 0,
shortcut: LogicalKeySet(
LogicalKeyboardKey.meta, LogicalKeyboardKey.digit0),
onClicked: () {
_setCounter(0);
}),
MenuDivider(),
MenuItem(
label: 'Increment',
shortcut: LogicalKeySet(LogicalKeyboardKey.f2),
onClicked: incrementCounter),
MenuItem(
label: 'Decrement',
enabled: _counter > 0,
shortcut: LogicalKeySet(LogicalKeyboardKey.f1),
onClicked: _decrementCounter),
]),
]);
}
@override
Widget build(BuildContext context) {
// Any time the state changes, the menu needs to be rebuilt.
updateMenubar();
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
primaryColor: _primaryColor,
accentColor: _primaryColor,
),
darkTheme: ThemeData.dark(),
home: _MyHomePage(title: 'Flutter Demo Home Page', counter: _counter),
);
}
}
class _MyHomePage extends StatelessWidget {
const _MyHomePage({required this.title, this.counter = 0});
final String title;
final int counter;
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(title),
),
body: LayoutBuilder(
builder: (context, viewportConstraints) {
return SingleChildScrollView(
child: ConstrainedBox(
constraints:
BoxConstraints(minHeight: viewportConstraints.maxHeight),
child: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
const Text(
'You have pushed the button this many times:',
),
new Text(
'$counter',
style: Theme.of(context).textTheme.headline4,
),
TextInputTestWidget(),
new ElevatedButton(
child: new Text('Test raw keyboard events'),
onPressed: () {
Navigator.of(context).push(new MaterialPageRoute(
builder: (context) => KeyboardTestPage()));
},
),
Padding(
padding: const EdgeInsets.all(8.0),
child: Container(
width: 380.0,
height: 100.0,
decoration: BoxDecoration(
border: Border.all(color: Colors.grey, width: 1.0)),
child: Scrollbar(
child: ListView.builder(
padding: EdgeInsets.all(8.0),
itemExtent: 20.0,
itemCount: 50,
itemBuilder: (context, index) {
return Text('entry $index');
},
),
),
),
),
],
),
),
),
);
},
),
floatingActionButton: FloatingActionButton(
onPressed: _AppState.of(context)!.incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
}
/// A widget containing controls to test text input.
class TextInputTestWidget extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Row(
mainAxisAlignment: MainAxisAlignment.center,
children: const <Widget>[
SampleTextField(),
SampleTextField(),
],
);
}
}
/// A text field with styling suitable for including in a TextInputTestWidget.
class SampleTextField extends StatelessWidget {
/// Creates a new sample text field.
const SampleTextField();
@override
Widget build(BuildContext context) {
return Container(
width: 200.0,
padding: const EdgeInsets.all(10.0),
child: TextField(
decoration: InputDecoration(border: OutlineInputBorder()),
),
);
}
}
After running the example application, hit the increment button which will then print 0 1 2 3 4 as well as the address of the pointer to the console.
I apologise if this seemed lazy but I'm not a flutter developer, I actually have zero experience in it and today was my first day touching it. But figuring out the basic code and syntax wasn't too difficult.
