Errors in ffigen

This file documents various errors and their potential fixes related to ffigen.

Errors in source header files

FFIgen uses libclang to parse header files. Any compiler warnings/errors should be logged (with SEVERE level). Compiler errors and warnings should be resolved as they can potentially generate invalid bindings that might cause silent errors and crashes at runtime.

You can pass in args to libclang using compiler-opts via cmd line or yaml config or both.

Here we'll list some common usecases. You can find the full list of supported args here.

Missing headers

These are the most common source file errors. You can specify include paths to clang like this

compiler-opts:
  - "-I/path/to/folder"

Ignoring source errors

As a last resort, you can pass in --ignore-source-errors or set ignore-source-errors: true in yaml config.

Warning: This will likely lead to incorrect bindings!

Errors in Objective-C bindings

Method not defined

ObjC's method naming is a bit different to Dart's. For example, NSString has a method stringWithCharacters:length:. To make invocation feel as similar to ObjC as possible, we generate this as a method named stringWithCharacters, with a named required parameter called length.

So one reason you might be having trouble invoking the method is that this naming convention is different to ObjC. The generated methods have a comment giving their full ObjC name, so you can try searching for that string to find the corresponding Dart method.

Since Dart doesn't support method overloading, the method may have been renamed to avoid collisions. Again the best approach is to search for the ObjC method name.

When ffigen generates bindings for an ObjC interface, eg Foo, it generates a Dart class Foo, which contains the constructor and static methods. The instance methods are generated in an extension, Foo$Methods.

So if you've searched for the generated method and found it, and still can't invoke it, it's possible that you've imported the class, Foo, but not the extension Foo$Methods. This can happen if you're using show/hide when you import the bindings. Make sure to import both Foo and Foo$Methods.