首次调用函数时，地图标记getPosition（）无法用于Google地图

Question

I'm trying to place a marker on my map and then use the position of that marker to draw some polygons. However, marker.getPosition() does not seem to return a value initially. I would need to call the function again to get the previous marker position. Does anyone have any suggestions as to why this is

function codeAddress() {
  var address = fubar;
  geocoder.geocode( { 'address': address}, function(results, status) {
      map.setCenter(results[0].geometry.location);
      map.setZoom(1);
      if (marker == null){
        marker = new google.maps.Marker({
          map: map,
        });
      }
      marker.setPosition(results[0].geometry.location);
  });
  document.write(marker.getPosition());   //this displays nothing
}

Answer 1

Google maps is using callbacks, ( see parameter 2 in the documentation ) because its not synchronous . The function(results,status) bit is where the magic happens. It is run when Google has geocoded the address. Untill then you have nothing to display.

try this:

function codeAddress() {
    var address = fubar;
    geocoder.geocode( { 'address': address}, function(results, status) {
        map.setCenter(results[0].geometry.location);
        map.setZoom(1);
        if (marker == null){
            marker = new google.maps.Marker({
                map: map,
            });
        }
        marker.setPosition(results[0].geometry.location);
        alert("Alert 1");
        alert(marker.getPosition());
    });
    alert("Alert 2");
}

And you will see that alert("Alert 2") appears before alert("Alert 1")

Answer 2

You could take advantage of $.Deferred()

function codeAddress() {
  var address = fubar;
  var d = $.Deferred();
  var marker;

  geocoder.geocode( { 'address': address}, function(results, status) {
      map.setCenter(results[0].geometry.location);
      map.setZoom(1);
      if (marker == null){
        marker = new google.maps.Marker({
          map: map,
        });
      }
      marker.setPosition(results[0].geometry.location);
      d.resolve();
  });
  d.done(function(){
      document.write(marker.getPosition());
  });
}