Question

I have the following Java interfaces,

public interface JavascriptInterface
{
    public MyIterator getItems();
}

public interface MyIterator
{
    public boolean hasNext();
    public String next();
}

which I expose as an API to a JavaScript web application:

Webview webview;
JavascriptInterface webapi;

//init webview and webapi [..]

webview.addJavascriptInterface(webapi, "webapi");

I wonder if there is a possibility to iterate over the items with a JavaScript for-loop like this:

for (var item in webapi.getItems())
{
    //do something with item [..]
}

What type/methods do I have to use/implement instead of MyIterator to make this possible, or can I convert it somehow (with a JavaScript helper)?
I currently return a String object with JSON and parse it with a JavaScript library. Is there an easier/faster solution?

Edit: The JSON solution also has the issue, that I can only provide a copy of static data and can not invoke methods.

Answer 1

If Android would fully support JavaScript version 1.7, I could to something like this, to map between Java and JavaScript Iterable (unfortunately they does not support it yet, but maybe this will work in the future):

function MyIterable(iterable)
{
    this.iterable = iterable;
}

MyIterable.prototype.__iterator__ = function() {
    return new MyIterator(this.iterable.iterator());
};

function MyIterator(iterator) {
    this.iterator = iterator;
}

MyIterator.prototype.next = function() {
    if (this.iterator.hasNext())
        return this.iterator.next();
    else
        throw StopIteration;
};

for (var item in new MyIterable(webapi.getItems()))
{
    //do something with item [..]
}

or

function createIterator(iterable)
{
    var iterator = iterable.iterator();
    while (iterator.hasNext())
        yield iterator.next();
    throw StopIteration;
}

for (var item in createIterator(webapi.getItems()))
{
    //do something with item [..]
}

Note: This time I assume webapi.getItems() returns a Java Iterable<T>.

I dont know if __iterator__() is a valid method name in Java, but you could also think about returning a custom Iterable/Iterator interface in Java, implementing __iterator__(), and next(). The only question is, how to throw the StopIteration exception.