flutter catching errors of nested async methods

Question

I have this method.

asyncFunction1() async {
  Firestore.instance.runTransaction((transaction){
    var first = await transaction.something;
    var second = await secondInside();
  });
}

Now I want to call this method, and catch every error that happens inside. How would I propagate errors so that

try {asyncFunction1()} catch(e){}

catches all errors that happened inside runTransaction?

Do you see a different behavior?

creativecreatorormaybenot
– creativecreatorormaybenot

2018-06-04 21:24:46 +00:00
Commented Jun 4, 2018 at 21:24 — creativecreatorormaybenot
– creativecreatorormaybenot, Commented Jun 4, 2018 at 21:24

Günter Zöchbauer · Accepted Answer · 2018-06-05 02:57:21Z

3

Your inner function misses an async to be able to use await. If you add it, you can use try/catch

asyncFunction1() {
  Firestore.instance.runTransaction((transaction) async {
    try {
      var first = await transaction.something;
      var second = await secondInside();
    } catch(e) {
      ...
    }
  });
}

answered Jun 5, 2018 at 2:57

Günter Zöchbauer

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5 Comments

Panda World Over a year ago

can you also give an example of how to catch this error in the future instance of the above async function?thanks

Günter Zöchbauer Over a year ago

Sorry, I don't understand your question. You just need to await the call and wrap it with try/catch.

Panda World Over a year ago

Apologize for the confusion. What I mean is if you have assigned this to a variable: Future<void> asyncFunction = asyncFunction1(); When we add asyncFunction.catchError((error){}), can this catch the exception that already caught in the above block?

Günter Zöchbauer Over a year ago

Why would you want to do this? I still don't think I understand the question but catchError is the canonical way of handling exceptions of async code, try/catch can only be used with async/await.

Panda World Over a year ago

The main reason for me is to trying to understand the relationship between future and async function.Maybe my example is bit confusing. Please let me give another one: Future<void> asyncFunction async{ try{...}catch{} } Future<void> asyncInstance = asyncFunction; asyncInstance.catchError((error){}); Hmm, the code is a bit hard to read, maybe i should create a question for it.

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