Dart / Flutter ffi（Foreig函数接口）本机回调，例如：sqlite3_exec [英] Dart/Flutter ffi (Foreig Function Interface) native callbacks eg: sqlite3_exec

问题描述

您好，我正在使用dart：ffi与本机c / c ++库建立接口。
，我需要一种从c到dart进行回调的方法，例如在sqlite中：

Hello I am using dart:ffi to build an interface with my native c/c++ library. and I needed a way to get a callback from c to dart as an example in sqlite:

int sqlite3_exec(
    sqlite3*,                                  /* An open database */
    const char *sql,                           /* SQL to be evaluated */
    int (*callback)(void*,int,char**,char**),  /* Callback function */
    void *,                                    /* 1st argument to callback */
    char **errmsg                              /* Error msg written here */
);

sqlite3_exec 中的第三个参数是函数指针回调。
，因此，如果我使用 ffi 在dart中调用此函数，则需要传递一个函数指针：在 dart：ffi Pointer 类中有一个名为 fromFunction 的函数，它接受dart静态函数和 exceptionalReturn ;但是只需调用此函数以获取dart托管函数的函数指针：就会产生（sigterm），并且dart代码在该过程中不再起作用。

the third parameter in sqlite3_exec is function pointer to a callback. so if I called this function in dart using ffi I need to pass a function pointer: and in dart:ffi Pointer class there is a function named fromFunction witch accepts a dart static function and an exceptionalReturn; but just by calling this function to get the function pointer of a dart managed function: a (sigterm) is raised and the dart code no long work in the process.

所以我的问题：有没有办法在dart中获得本机回调，如Python，c＃，..

So My Question: Is there any way to get a native callback in dart, as in Python, c#, ..

额外：
是否可以在 flutter 项目中包含 dartino ，因为此 ForeignDartFunction 涵盖了我的需要。

Extra: Is there any way to include dartino in a flutter project, since this ForeignDartFunction covers what I need.

推荐答案

我有一个工作示例。希望您可以根据情况进行调整。

I got an example to work. Hopefully you can adapt this to your case.

示例C函数

EXTERNC int32_t foo(
                    int32_t bar,
                    int32_t (*callback)(void*, int32_t)
                    ) {
    return callback(nullptr, bar);
}

飞镖代码

首先是 typedefs 。对于本地函数 foo ，我们需要两个，对于Dart回调，我们需要一个。

First the typedefs. We need two for the native function foo and one for the Dart callback.

typedef example_foo = Int32 Function(
    Int32 bar, Pointer<NativeFunction<example_callback>>);
typedef ExampleFoo = int Function(
    int bar, Pointer<NativeFunction<example_callback>>);

typedef example_callback = Int32 Function(Pointer<Void>, Int32);

以及回调代码

  static int callback(Pointer<Void> ptr, int i) {
    print('in callback i=$i');
    return i + 1;
  }

和查找

  ExampleFoo nativeFoo =
    nativeLib.lookup<NativeFunction<example_foo>>('foo').asFunction();

最后，像这样使用它：

  int foo(int i) {
    return nativeFoo(
      i,
      Pointer.fromFunction<example_callback>(callback, except),
    );
  }

如预期的那样， foo（123）在回调i = 123 中显示 flutter：并返回 124

as expected, foo(123) prints flutter: in callback i=123 and returns 124

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