在 Flutter Windows 桌面应用程序中使用 C++ DLL

Question

我有一些库可以与 FTDI 芯片交互，我将其打包到 C++ 中的 DLL 中。 我想用 Flutter 创建一个前端，并在 windows 桌面应用程序中使用该库。 这些功能在 Flutter 中仍然是新功能，并且文档非常浅显且特定于移动设备。

按照此处的指南，我使用 FFI 创建了一个插件：

import 'dart:ffi';
import 'dart:io';
import 'dart:async';

import 'package:flutter/services.dart';

final DynamicLibrary FT232H = DynamicLibrary.open("");

final int Function() initializeLibrary = FT232H
    .lookup<NativeFunction<Uint8 Function()>>("initialize_library")
    .asFunction();

final void Function() cleanupLibrary = FT232H
    .lookup<NativeFunction<Void Function()>>("cleanup_library")
    .asFunction();

final int Function() initializeI2C = FT232H
    .lookup<NativeFunction<Uint8 Function()>>("Initialize_I2C")
    .asFunction();

final int Function() closeI2C = FT232H
    .lookup<NativeFunction<Uint8 Function()>>("Close_I2C")
    .asFunction();

final int Function(
        Uint8 slaveAddress, Uint8 registerAddress, Uint32 data, Uint32 numBytes)
    i2cWriteBytes = FT232H
        .lookup<NativeFunction<Uint8 Function(Uint8, Uint8, Uint32, Uint32)>>(
            "I2C_write_bytes")
        .asFunction();

final int Function(Uint8 slaveAddress, Uint8 registerAddress,
        Uint8 bRegisterAddress, Pointer<Uint8> data, Uint32 numBytes)
    i2cReadBytes = FT232H
        .lookup<
            NativeFunction<
                Uint8 Function(Uint8, Uint8, Uint8, Pointer<Uint8>,
                    Uint32)>>("I2C_read_bytes")
        .asFunction();

class DllImport {
  static const MethodChannel _channel = const MethodChannel('dll_import');

  static Future<String> get platformVersion async {
    final String version = await _channel.invokeMethod('getPlatformVersion');
    return version;
  }
}

这是我在另一边的 header 文件：

#pragma once

/* Include D2XX header*/
#include "ftd2xx.h"

/* Include libMPSSE headers */
#include "libMPSSE_i2c.h"
#include "libMPSSE_spi.h"

#define FT232H_EXPORTS

#ifdef FT232H_EXPORTS
#define FT232H_API __declspec(dllexport)
#else
#define FT232H_API __declspec(dllimport)
#endif


extern "C" FT232H_API uint8 initialize_library();
extern "C" FT232H_API void cleanup_library();
extern "C" FT232H_API FT_STATUS Initialize_I2C();
extern "C" FT232H_API FT_STATUS Close_I2C();
extern "C" FT232H_API FT_STATUS I2C_write_bytes(uint8 slaveAddress, uint8 registerAddress, 
const uint8 * data, uint32 numBytes);
extern "C" FT232H_API FT_STATUS I2C_read_bytes(uint8 slaveAddress, uint8 registerAddress, 
uint8 bRegisterAddress, uint8 * data, uint32 numBytes);

在这里，我似乎对 Uint8 指针有一些问题，因为我从我的 Dart 代码中得到了这个错误：

The type 'Uint8 Function(Uint8, Uint8, Uint8, Pointer<Uint8>, Uint32)' must be a subtype of 'int 
Function(Uint8, Uint8, Uint8, Pointer<Uint8>, Uint32)' for 'asFunction'.
Try changing one or both of the type arguments.dart(must_be_a_subtype)

任何有关如何在 flutter 中实现这一点的指针将不胜感激！

谢谢你。

Answer 1

我确实有一个解决方案，它适用于 Flutter-Desktop-Embedding 项目中提供的准系统代码，我假设您将其用于您的桌面应用程序。 你在正确的轨道上，但只需要一些最终确定。

为了测试，我使用这个简单的 c 代码和几个函数来测试传递指针、返回指针、填充 memory、分配和释放。 这是我在 dll 中使用的 C 代码。

#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分配给定大小的 uint8_t 指针并将其返回给调用者。

populatearray采用 uint8_t 指针参数和大小并用索引填充它

destroyarray简单地释放分配的 memory。

现在为样板 flutter 代码。

这是我在 Flutter-Desktop-Embedding 项目中为main.dart提供的默认代码，我从这里克隆了https://github.com/google/flutter-desktop-embedding.git （假设您已经完成了这一步）

// 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.

我们将需要 dart:io 和 dart:ffi 包。 dart:io 已经在代码中，只需要导入 dart:ffi import 'dart:ffi'; // For FFI import 'dart:ffi'; // For FFI

现在要创建需要加载的库的句柄，需要使用名称 dll 调用 DynamicLibrary.open。 （dll需要放在dart应用的执行路径下或者需要给出绝对路径，执行路径为build/windows/runner/Debug）

final DynamicLibrary nativePointerTestLib = DynamicLibrary.open("dynamicloadtest.dll");

我的句柄被称为nativePointerTestLib ，dll 的名称是“dynamicloadtest.dll”（是的，我可能应该使用更好的命名约定）

接下来，需要创建每个 function 指针。 我要调用的dll中有三个函数：createarray、populatearray、destroyarray。

第一个采用 int 的 size 参数 -> 返回指向数组的指针 (Pointer) 第二个采用指针以及 size -> void return 第三个仅采用指针 -> 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();

我将 function 指针命名为nativeCreateArray 、 nativePopulateArray 、 nativeDestroyArray

最后，只需调用每个 function 并测试它们是否有效。 我刚刚在样板代码中随机选择了一个 function， void _setCounter(int value)设置计数器值，然后显示。 我只是要向该方法添加额外的代码来执行我们的 function 调用以及打印结果以查看它是否有效。 旧方法

void _setCounter(int value) {
    setState(() {
      _counter = value;
    });
  }

使用我们的 function 调用的新方法

  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;
    });
  }

我调用了大小为 5 的 nativeCreate。dll 将为数组分配 5 个字节。

接下来我调用 populate，它将在数组的每个元素中插入索引 0 到 4。

然后我遍历数组，获取该数组索引处的每个元素，然后获取值。 我将该值分配给一个字符串，最后打印并销毁该数组。

最终代码将所有内容放在一起：

// 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()),
      ),
    );
  }
}

运行示例应用程序后，点击增量按钮，然后将打印 0 1 2 3 4 以及指向控制台的指针地址。

如果这看起来很懒，我深表歉意，但我不是 flutter 开发人员，我实际上在这方面的经验为零，今天是我接触它的第一天。 但是弄清楚基本的代码和语法并不太难。