JSLIB wait to receive variables from javascript

Hi,
I have a JSLIB script working with Unity.

I call it as simple as this.

Code (CSharp):

1. string receivedString = "";
2. receivedString = GetValueFromJsLib();

The jslib is getting called however the code doesn't wait for the variable receivedString to receive the value from jslib and hence I always get a blank value in receivedString. I have made sure to check if I am receiving the value from jslib through console.

How can I wait till the variable receivedString receives the value?

Regards

 

I can not make much sense of what you wrote ^^. When you call a nativ javascript function from C# it is executed synchonously. So the return value of your method will for sure arrive properly. However since you want to return a string you probably do it the wrong way. Keep in mind that C# is a managed language. C# Strings live on the managed heap which is "emulated" in a WebGL build. You can not simply return a javascript string to C#. There's an example in the documentation. Specifically:

Code (CSharp):

1. StringReturnValueFunction: function () {
2.     var returnStr = "bla";
3.     var bufferSize = lengthBytesUTF8(returnStr) + 1;
4.     var buffer = _malloc(bufferSize);
5.     stringToUTF8(returnStr, buffer, bufferSize);
6.     return buffer;
7.   },

So you have to use _malloc to allocate the actual managed string object on the managed heap and copy the data using "stringToUTF8"

 

Thanks for the response. And yes I have taken care of this already. This is how my jslib code looks like.

Code (CSharp):

1. mergeInto(LibraryManager.library, {
2. GetLoc: function (){
3.    navigator.geolocation.getCurrentPosition(function(pos)
4.    {
5.     var coors = pos.coords.latitude+", "+pos.coords.longitude;
6.     console.log("COOOR "+coors);
7.            var returnStr = coors;
8.     var bufferSize = lengthBytesUTF8(returnStr) + 1;
9.     var buffer = _malloc(bufferSize);
10.     stringToUTF8(returnStr, buffer, bufferSize);
11.     console.log("buffer "+buffer);
12.     return buffer;
13.     });
14. },
15. });

 

Well, that doesn't work at all ^^. The getCurrentPosition method seems to be an asynchronous call and all your code is inside the callback of that async call. Returning something from such a callback makes no sense at all ^^.

Such an asynchronous call can not be made synchronous. So you have two options here:

Either split the whole process into a two method process, so the first one starts the async task, you store the result in a JS variable and the second method call just reads out the last received value.

Another option is to actually use a callback. The simplest way would be to use SendMessage, though that's somewhat messy. It should be able to actually directly call a C# delegate from your callback. I have never tested this, but it should be something like this:

Code (CSharp):

1.  
2.     mergeInto(LibraryManager.library, {
3.     GetLoc: function (callback){
4.         navigator.geolocation.getCurrentPosition(function(pos) {
5.             var coors = pos.coords.latitude+", "+pos.coords.longitude;
6.             console.log("COOOR "+coors);
7.             var returnStr = coors;
8.             var bufferSize = lengthBytesUTF8(returnStr) + 1;
9.             var buffer = _malloc(bufferSize);
10.             stringToUTF8(returnStr, buffer, bufferSize);
11.             Runtime.dynCall('vi', callback, [buffer]);
12.         });
13.     }
14.     });
15.  

Now our GetLoc method does not return anything (well, it never did in the first place) but instead requires a callback that takes a string as argument. So the signature on the C# side should look something like this:

Code (CSharp):

1.  
2.     [DllImport("__Internal")]
3.     public static extern void GetLoc(Action<string> aCallback);
4.  

So calling GetLoc would still not return any string since it can't. However the asynchronous JS call should call our callback when the request has finished. Something like that:

Code (CSharp):

1.  
2. void SomeMethod()
3. {
4.     GetLoc((location) => {
5.         Debug.Log("Location from JS: " + location);
6.     });
7. }

 

Thanks @Bunny83. That worked. Appreciate the help.

 

Hello I tried that and get an error: IL2CPP does not support marshaling delegates that point to instance methods to native code. The method we're attempting to marshal is: TestJS+<>c::<SomeMethod>b__5_0.
Any help is appreciated.

 

Getting the same IL2CPP error mentioned above. Is there a known solution to this?