man*_*j82 17 javascript google-maps geocoding
当我使用下面的代码警告空值时？这是为什么？
HTML
<body onload="initialize()">
<div id="map_canvas" style="width: 320px; height: 480px;"></div>
<div>
<input id="address" type="textbox" value="Sydney, NSW">
<input type="button" value="Encode" onclick="display()">
</div>
</body>
JavaScript的
var geocoder;
var map;
function initialize() {
geocoder = new google.maps.Geocoder();
var latlng = new google.maps.LatLng(-34.397, 150.644);
var myOptions = {
zoom: 8,
center: latlng,
mapTypeId: google.maps.MapTypeId.ROADMAP
}
map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);
}
function codeAddress() {
var address = document.getElementById("address").value;
var loc=[];
geocoder.geocode( { 'address': address}, function(results, status) {
if (status == google.maps.GeocoderStatus.OK) {
loc[0]=results[0].geometry.location.lat();
loc[1]=results[0].geometry.location.lng();
} else {
alert("Geocode was not successful for the following reason: " + status);
}
});
return loc;
}
function display(){
var long_lat=codeAddress();
alert(long_lat);
}
Max*_*xym 26
因为你的函数codeAddress被执行时,分配空数组为LoC,执行异步请求,以谷歌地理编码器并返回LOC,里面是空的,因为当从谷歌响应来自它的真实值被分配.换句话说,allert应该在内部响应处理程序中:
var geocoder;
var map;
function initialize() {
geocoder = new google.maps.Geocoder();
var latlng = new google.maps.LatLng(-34.397, 150.644);
var myOptions = {
zoom: 8,
center: latlng,
mapTypeId: google.maps.MapTypeId.ROADMAP
}
map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);
}
function codeAddress() {
var address = document.getElementById("address").value;
var loc=[];
// next line creates asynchronous request
geocoder.geocode( { 'address': address}, function(results, status) {
// and this is function which processes response
if (status == google.maps.GeocoderStatus.OK) {
loc[0]=results[0].geometry.location.lat();
loc[1]=results[0].geometry.location.lng();
alert( loc ); // the place where loc contains geocoded coordinates
} else {
alert("Geocode was not successful for the following reason: " + status);
}
});
// pretty meaningless, because it always will be []
// this line is executed right after creating AJAX request, but not after its response comes
return loc;
}
function display(){
codeAddress();
}
这就是AJAX的工作原理...处理回调处理程序的结果.
如果你想分开地理编码和'dispalying'你可以在处理程序中执行显示功能:
function codeAddress() {
var address = document.getElementById("address").value;
geocoder.geocode( { 'address': address}, function(results, status) {
if (status == google.maps.GeocoderStatus.OK) {
var loc=[]; // no need to define it in outer function now
loc[0]=results[0].geometry.location.lat();
loc[1]=results[0].geometry.location.lng();
display( loc );
} else {
alert("Geocode was not successful for the following reason: " + status);
}
});
}
function display( long_lat ){
alert(long_lat);
}
HTML:
<input type="button" value="Encode" onclick="codeAddress()">
codeAddress函数的参数:
function codeAddress( callback ) {
...
geocoder.geocode( { 'address': address}, function(results, status) {
...
callback( loc ); // instead of dispaly( loc );
...
}
...
}
codeAddress( display ); // to execute geocoding
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