在react-native / expo中的异步函数中访问const

Question

I am trying to use the expo-av lib

I use the following async function to play a sound file from an URL:

PlaySound = async (soundURL) => {
    try { 
        const playbackObject = await Audio.Sound.createAsync(
            { uri: soundURL },
            { shouldPlay: this.state.shouldPlay }
        );
     } catch (error) {
           console.log('ERROR:'+error);
           // Error retrieving data
     }

    return playbackObject;
};


stopSound = async (soundURL) => {
try {

  this.setState({shouldPlay:false});
   const playbackObject = await PlaySound(soundURL);

 } catch (error) {
  console.log('ERROR:'+error);
  // Error retrieving data
}
playbackObject.stopAsync(); // this is causing the error
};

I get this error:

ERROR:ReferenceError: Can't find variable: playbackObject

[Unhandled promise rejection: ReferenceError: Can't find variable: playbackObject]

The PlaySound functions works as I want. Now I want to be able to pause/stop using the stopSound function. The documentation says to use soundObject.stopAsync() which in my case would be playbackObject . But I can't figure out how to access this const outside of the function?

Can anyone point me in the right direction?

Answer 1

You cannot reference a const that was defined inside of a try/catch outside of the try catch. You can fix this by doing either of the following:

let playbackObject;

try { 
  playbackObject = await Audio.Sound.createAsync(
    { uri: soundURL },
    { shouldPlay: this.state.shouldPlay }
  );
} catch (error) {
  console.log('ERROR:'+error);
  // Error retrieving data
}

return playbackObject;

or

try { 
  return Audio.Sound.createAsync(
    { uri: soundURL },
    { shouldPlay: this.state.shouldPlay }
  );
} catch (error) {
  console.log('ERROR:'+error);
  // Error retrieving data
}

In order to fix the stop function, you should maintain a reference to the playbackObject that is returned by the start function and use that in the stop function, since the way you currently have it would create a new audio stream that you would then stop (leaving the original in tact).