谷歌地圖API地理編碼功能問題

Question

好吧，我與Google Maps API v3鬼混，我遇到了一個問題。我不知道它的API或只是我犯的一些JS錯誤。

問題： addMarkerFromAdress()函數調用geocodeFromAdress()返回的座標返回到addMarkerFromAdress()。但返回的值是「undefined」。

作爲一個調試我添加了兩個警報輸出，一個在addMarkerFromAdress()和一個在geocodeFromAdress()。讓我感到困擾的是，addMarkerFromAdress()中的alert()似乎在返回任何值之前觸發。爲什麼？

來源：

<script type="text/javascript"> 
    var geocoder; 
    var map; 

    function initializeGoogleMaps() { 

    geocoder = new google.maps.Geocoder(); 
    var latlng = new google.maps.LatLng(0, 0); 
    var myOptions = { 
     zoom: 1, 
     center: latlng, 
     mapTypeId: google.maps.MapTypeId.ROADMAP 
    } 

    map = new google.maps.Map(document.getElementById("map_canvas"), myOptions); 

    } 

    function geocodeFromAdress(address) { 
    geocoder.geocode({ 'address': address}, function(results, status) { 
     if (status == google.maps.GeocoderStatus.OK) { 
     var latLng = results[0].geometry.location; 
     alert(latLng); //Outputs coordinates, but is for some reason outputted 2nd 
     return latLng; 
     } else { 
     alert("Geocode was not successful for the following reason: " + status); 
     } 
    }); 
    } 

    function addMarkerFromAdress(address, title){ 

    var latLng = geocodeFromAdress(address); 
    alert(latLng); //Outputs "undefined", but is for some reason outputted 1st 
    map.setCenter(latLng); 
     var marker = new google.maps.Marker({ 
      map: map, 
      position: latLng 
    }); 

    } 

    window.onload = function() { 
    initializeGoogleMaps(); 
    addMarkerFromAdress('Berlin, Germany', 'Berlin'); 
    } 
</script> 

Answer 1

請參閱函數作爲第二個參數傳遞geocoder.geocode()？那就是你應該打電話給addMarkerFromAddress的地方。由於地理編碼請求的異步性質，var latLng = geocodeFromAdress(address);之後的alert在響應以緯度長的值返回之前觸發。

像這樣的事情應該去做

<script type="text/javascript"> 
    var geocoder; 
    var map; 

    function initializeGoogleMaps() { 

    geocoder = new google.maps.Geocoder(); 
    var latlng = new google.maps.LatLng(0, 0); 
    var myOptions = { 
     zoom: 1, 
     center: latlng, 
     mapTypeId: google.maps.MapTypeId.ROADMAP 
    } 

    map = new google.maps.Map(document.getElementById("map_canvas"), myOptions); 

    } 

    function geocodeFromAdress(address, title) { 
    geocoder.geocode({ 'address': address}, function(results, status) { 
     if (status == google.maps.GeocoderStatus.OK) { 
     var latLng = results[0].geometry.location; 
     addMarkerFromAdress(latLng, title); 
     } else { 
     alert("Geocode was not successful for the following reason: " + status); 
     } 
    }); 
    } 

    function addMarkerFromAdress(latLng, title){ 
    map.setCenter(latLng); 
    var marker = new google.maps.Marker({ 
     map: map, 
     position: latLng 
    }); 
    } 

    window.onload = function() { 
    initializeGoogleMaps(); 
    geocodeFromAdress('Berlin, Germany', 'Berlin'); 
    } 
</script>