How to send a callback from Android to Javascript function?

Question

I am trying to call an Android native function "refreshPages" from JS function "refreshPagesWithIds" which passes an array of strings to native.

id: ["1","2"];
refreshPagesWithIds(id) {
  return Android.refreshPages(id);
}

The Android native function "refreshPages" internally calls a method "someFunction" which takes id array as argument and returns a Promise after refreshing the pages.

@JavascriptInterface
    public void refreshPages(String[] ids) {
        StorageModule.someFunction(ids, null);
    }

someFunction looks like:

@JvmStatic
    fun someFunction(pageIds: ReadableArray, promise: Promise? = null) {
        val storagePromise = StoragePromise(promise, storageModules.size)
        storageModules.forEach { module -> module.refreshPagesWithIds(pageIds, storagePromise) }
    }

How can I return a value when the Promise from refreshPages function(in native) gets settled to Javascript? I am unable to understand the implementation for public void refreshPages(String[] ids)

ehab · Accepted Answer · 2021-07-25 11:33:01Z

A java promise is different than a javascript promise, the only thing related between them is the name. You can not return a promise from java to javascript, even if syntax enables that you will be sending a serialised cloned object which has no relation to the one in java - the one in java might be completed, but you wont know about that in javascript.

What you could do is in javascript something like this

arePagesRefereshed: true
id: ["1","2"];
refreshPagesWithIds(id) {
  // this seems to be sitting in an object, so i am just assuming that this refers to the object, but you get the point
  this.arePagesRefereshed = false
  return Android.refreshPages(id);
},
markPagesAsRefereshed: () => {
  this.arePagesRefereshed = true

}

and then in Java

@JvmStatic
    fun someFunction(pageIds: ReadableArray, promise: Promise? = null) {
        val storagePromise = StoragePromise(promise, storageModules.size)
        storageModules.forEach { module -> module.refreshPagesWithIds(pageIds, storagePromise) }
    // after all promises are completed call markPagesAsRefereshed in javascript
    }

When promise in Android gets resolved, how can I send value to JS?
@AashnaNarula Well call a javascript function with that value, for example call markPagesAsRefereshed(resolvedValue)

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