[mapguide-users] Re: Getting layer's maxscale to Viewer API
Johannes Foell
jfoell at uos.de
Wed Feb 24 04:24:27 EST 2010
Thank you Kenneth for your great help.
I've solved it with the public variable.
Best regards,
Johannes Foell
Kenneth Skovhede, GEOGRAF A/S wrote:
>
> Performance of codebehind is much better, and so is the general
> dependency etc. If at all possible, I recommend that you use codebehind.
> Also, when writing ajax handlers, be sure to use .ashx as they have less
> overhead than
> the .aspx pages.
>
> In your code (regardless of where it is placed), you can either
> use the public variable approach I outlined, or use the "response.write"
> method to write data to the output stream.
>
> Try to install and use FireBug (for FireFox) or Fiddler (for IE),
> with either tool, you can see the data being transfered, and that should
> help you understand what data you are transmitting.
>
> I'm not sure why you use the JavaScripSerializer, as you already have
> the string in a JSON format?
> The value should not be enclosed in strings, eg, it should be:
> Dim MString as String = "{""scale:""" &
> MaxSC.ToString(System.Globalization.CultureInfo.InvariantCulture) & "}"
>
> Then:
> Response.Clear()
> Response.Write(MString)
> Response.Flush()
> Response.End()
>
> In the JS code, you attempt to do something directly after you issue the
> AJAX call.
> Since AJAX is async you do not yet have the data.
> You must wait for the data to be fetched from the server, which is what
> the
> onreadystatechanged function is for.
>
> Inside this function, you "unwrap" the JSON string into a javascript
> object.
> Your maxsc2 variable is the object, so you can call:
>
> var scale = maxsc2.scale; //Your code names the variable "double", eg:
> var scale = maxsc2.double;
> parent.KartenFrame.viewerFrame.mapFrame.ZoomToView(xcoord,ycoord,scale,true);
>
> Remember that the code after request.send() gets executed immediately, and
> does NOT wait for the server to finish processing.
>
> You must do all the processing inside the onreadystatechanged function.
> Once the data is returned, you can call the zoom function, but not before.
>
> I recommend that you also send the x/y values back and forth, so you can
> easily access them
> inside the onreadystatechanged callback. Otherwise you need to worry
> about function scopes
> and javascript enclosures (advanced JS topic).
>
> I recomend that you use some JS framework to achieve this, as that will
> handle function scope better than the raw method you use here.
> A JS framework will also give you a nice error handler, and will be
> cross browser.
>
> Prototype seems to be popular:
> http://www.prototypejs.org/api/ajax/request
>
> It's ajax request object has "onSuccess" and "onFailure", so
> you can give the user a nice message if the server fails, or the network
> link breaks.
>
> Regards, Kenneth Skovhede, GEOGRAF A/S
>
> On 18-02-2010 15:57, Johannes Foell wrote:
>> You have exactly pointed out what i need.
>>
>> Unfortunately I'm using code inline and not codebehind. The first way,
>> which
>> you presented doesn't work in my code.
>>
>> As newbie to JSON i've tested your second solution, but i do'nt get the
>> scale to the client there, too.
>> Does anyone here knows, how to deliver a JSON-object from the server to
>> the
>> client? What is wrong in my code?
>>
>> The important lines are:
>> In VB.NET:
>>
>> Sub reload (ByVal o As Object, ByVal e As EventArgs)
>>
>> MaxSc is the double-variable, which contains the MaxScale for the
>> Layer.
>>
>> Dim MString As String = "{" + Chr(34) + "double" + Chr(34) + ":" +
>> Chr(34)
>> + MaxSc.ToString + Chr(34) + "}" ' e.g. the JSON-Object:
>> {"double":"31456.57"}
>>
>> Dim serializer As New JavaScriptSerializer
>>
>> Dim json As String = serializer.Serialize(MString)
>> End Sub
>>
>>
>> In JS:
>>
>> function ZoomToView()
>> {
>> var url; //the current aspx-file
>> var maxsc;
>> var maxsc2;
>> try {
>> var request = new XMLHttpRequest();
>> } catch(ex) {
>> try {
>> var request = new ActiveXObject("MSXML2.XMLHTTP");
>> } catch (ex) {
>> var request = new ActiveXObject("Microsoft.XMLHTTP");
>> }
>> }
>> request.onreadystatechange = function() {
>>
>> if(request.readyState == 4) {
>> maxsc2 = eval("(" + request.responseText + ")"); //what do i have to
>> call
>> here?
>> }
>> }
>> request.open("GET", url, true);
>> request.send();
>> maxsc = maxsc2.double; //the double-field of the object
>> maxsc -= 0.1; //to show the layer in the map
>> parent.KartenFrame.viewerFrame.mapFrame.ZoomToView(xcoord,ycoord,maxsc,true);
>> //the coordinates are no problem. if i set here a number as maxsc, e.g.
>> 15000, it works
>> }
>>
>>
>>
>> Thanks for any help.
>> Regards,
>> Johannes Foell
>>
>>
>>
>> Kenneth Skovhede, GEOGRAF A/S wrote:
>>
>>> Not sure this is what you are asking but, this is how I understand your
>>> question.
>>>
>>> Basically the output of an ASPX page is html (or any format really).
>>> Since you want to output the scale, you would want the following html
>>> output:
>>> <html><body><script>
>>> var maxScale =<%=serverGeneratedMaxScale%>;
>>> GetMap().ZoomToView(x, y, maxScale);
>>> </script></body></html>
>>>
>>> (I've left out the GetMap() and x, y code).
>>>
>>> The<%=serverGeneratedMaxScale%> gets processed by the ASP.Net runtime,
>>> and inserts the value of the variable named "serverGeneratedMaxScale" in
>>> th output.
>>>
>>> In your codebehind file, just declare a public instance variable with
>>> that name,
>>> and insert the above code in the aspx (below the codebehind
>>> declaration),
>>> and it should come out.
>>>
>>>
>>> Another slightly more sophisticated way of doing this, is to issue and
>>> AJAX call
>>> and have the page return a JSON object string like:
>>> {x: 333, y: 444, maxScale: 555}
>>>
>>> Then in your Ajax callback handler do this:
>>> var obj = eval('(' + responseText + ')');
>>> GetMap().ZoomToView(obj.x, obj.y, obj.maxScale);
>>>
>>> I can't remember what the AJAX stuff is called in the viewer, but there
>>> are
>>> plenty of free AJAX helper code avalible online.
>>>
>>> The benefit of using an AJAX call is that the user cannot pres "back",
>>> there is no "click" sound, and you don't need to mess with hidden
>>> frames.
>>>
>>> Regards, Kenneth Skovhede, GEOGRAF A/S
>>>
>>> On 15-02-2010 16:25, Johannes Foell wrote:
>>>
>>>> Hi List,
>>>>
>>>> I'm new to MG (and JS) and have a question about the layer's maxscale.
>>>> I
>>>> can
>>>> read the maxscale out of the Layerdefinition using a XML-File. Having
>>>> the
>>>> maxscale read out for each layer, I need the highest maximum for the
>>>> layergroup at the Viewer API to zoom to a given coordinate and this
>>>> maxscale.
>>>> Currently i compare the different maxscales and save the largest number
>>>> as
>>>> double. Writing this double to a new XML-File, i can't read it to the
>>>> Viewer
>>>> API.
>>>>
>>>> Is there a way to get this maxscale to the Viewer API and the method
>>>> ZoomToView()?
>>>>
>>>> I'm using VB.Net and JS.
>>>>
>>>> Or is there just another solution?
>>>>
>>>> Thanks for any hint in advance.
>>>> Best regards,
>>>> Johannes Foell
>>>>
>>>>
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>>>
>>>
>>>
>>
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