How do I use this async function's callback parm to know when my function finished executing?-CodePudding

New to flutter and async programming in general. I want to use this function:

https://pub.dev/documentation/ffmpeg_kit_flutter/latest/ffmpeg_kit/FFmpegKit/executeAsync.html

I don't understand the part that says

You must use an FFmpegSessionCompleteCallback if you want to be notified about the result.

Can someone explain how to use this as if I was a beginner programmer? Is this parameter something I can use to print a simple message to the console, like 'execution finished'?

What I've tried so far:

String test1() {
    return 'FFMPEG FINISHED';
  }

...later in the code

await FFmpegKit.executeAsync('ffmpeg -i '   FileDir.path   currentFilename   ' '   FileDir.path   currentOutputFilename   '.mp3', test1());

This gives an error pointing to the end of the await FFmpegKit... line: The argument type 'String' can't be assigned to the parameter type 'void Function(FFmpegSession)?'.

CodePudding user response：

The callback will be invoked when the operation completes. However, when you do

await FFmpegKit.executeAsync(..., test1());

you're not passing a callback. Instead, you're invoking your function yourself and passing the result (which fails with a type error).

You need to pass the function itself, not the result of invoking it:

await FFmpegKit.executeAsync(..., test1);

Additionally, your test1 callback has the wrong signature, and it will not do anything since it just returns a value that won't be used anywhere. You therefore need to make an additional change:

void test1(FFmpegSession session) {
  print('FFMPEG FINISHED');
}