Associate an object with Marker (google map v2)

Question

In my app I have some objects that have their location displayed on the map using markers. The problem is that the only way I've found to handle marker clicks is

googleMap.setOnMarkerClickListener(new ... {
    @Override
    public void onMarkerClick(Marker marker) {
       // how to get the object associated to marker???
    }
})

In other words I get the Marker object while the only interface that I have allows me to set just MarkerOptions.

Any way to associate Marker with an object?

Courtenay

Answer 1

You can associate arbitrary object by using Marker's setTag() method

Marker amarker = mMap.addMarker(new MarkerOptions().position(lat, lng).title("Hello World"));
amarker.setTag(new SomeData());

To retrieve data associated with marker, you simply read it using its getTag() and then cast it to its original type.

SomeData adata = (SomeData) amarker.getTag();

More information

Devy

This is the correct solution. As per documentation about Tag in Marker : "An Object associated with the marker. For example, the Object can contain data about what the marker represents. This is easier than storing a separate Map<Marker, Object>. " – Shockey

Correct solution as of Play Services 9.4 – Countersubject

This is the RIGHT solution! – Nectarine

That's great that after 4 years they've implemented this out-of-the-box =) – Courtenay

Answer 2

I reckon this callback was not very thoroughly though by the Android team, but, it's what we have.

Whenever you call mMap.addMarker(); it returns the generated marker. You can then use a HashMap or some other data holder structure to remember it.

// Create the hash map on the beginning
WeakHashMap <Marker, Object> haspMap = new WeakHashMap <Marker, Object>();


// whenever adding your marker
Marker m = mMap.addMarker(new MarkerOptions().position(lat, lng).title("Hello World").icon(icon_bmp));
haspMap.put(m, your_data);

Dubuffet

I recommend WeakHashMap, so when a Marker gets garbage-collected, so will its associated WeakHashMap entry and Object value. But, yes, unfortunately this seems to be the only option at present. – Gerhardt

makes sense to me. I edited my answer to be WeakHashMap. Is that ok? – Dubuffet

bzzzzt, wrong! I had to use an HashMap, otherwise the mapping gets somehow garbage collected. – Stokehold

The documentation says that marker object may change, so don't use the marker as the key, use m.getId(). – Stokehold

hi @Stokehold , I can't find that on the documentation. Could you point to a link, please? – Dubuffet

@Stokehold If you do so, you have no chance to remove the marker because you don't have the reference. – Haigh

@Gerhardt unless you use this WeakHashMap throughout the app it is not useful for this purpose. – Lepage

Answer 3

Another option would be to create a Map whose keys is marker.getId() and the value is our object.

In this way, we wouldn't keep a reference to a Marker in memory, and wouldn't have to worry about garbage collected markers.

Here you can see more answers.

Minute