Using a JavaScript callback function as a parameter for the addJavascriptInterface method in Java

Question

Using a JavaScript callback function as a parameter for the addJavascriptInterface method in Java

Can Java interact with arbitrary functional objects in JavaScript by calling them as callbacks?

For example, if we have a function called 'access' that is registered to invoke a Java function:

access(function(blabla){
    ...
});

Are there effective techniques for handling anonymous callback functions in Java?

javascript android crosswalk

Answer 1

Answer №1

One way to manage individual callback anonymous functions is by using a key for reference, similar to how jsonp operates at times.

JavaScript:

var callbacks = [];
function registerCallback(callback)
{
   callbacks.push(callback);
   return callbacks.length - 1;
}

function getCallback(index)
{
   var callback = callbacks[index];
   callbacks[index] = null;

   TryGCCallbacks();

   return callbacks;
}

//Ensuring preservation of array index positions and resetting the array when empty
function TryGCCallbacks()
{
   var isCallbackRemaining = false;
   for (var i = 0; i < callbacks.length; i++)
   {
      if (callbacks[i] == null) {
         continue;
      }

      isCallbackRemaining = true;
      break;
   }
   if (isCallbackRemaining == false)
   {
      callbacks = []; //reset
   }
}

Java:

@org.xwalk.core.JavascriptInterface
public String TestCallback(String someData, String onSuccess, String onError){
   xwalk.evaluateJavascript("getCallback(" + onSuccess + ")('success');", null);
}

Using this with JavaScript:

var onSuccess = registerCallback(function(r) {
   console.log(r);
});

TestCallback('lalala', onSuccess, null);

Answer 2

One way to manage individual callback anonymous functions is by using a key for reference, similar to how jsonp operates at times.

JavaScript:

var callbacks = [];
function registerCallback(callback)
{
   callbacks.push(callback);
   return callbacks.length - 1;
}

function getCallback(index)
{
   var callback = callbacks[index];
   callbacks[index] = null;

   TryGCCallbacks();

   return callbacks;
}

//Ensuring preservation of array index positions and resetting the array when empty
function TryGCCallbacks()
{
   var isCallbackRemaining = false;
   for (var i = 0; i < callbacks.length; i++)
   {
      if (callbacks[i] == null) {
         continue;
      }

      isCallbackRemaining = true;
      break;
   }
   if (isCallbackRemaining == false)
   {
      callbacks = []; //reset
   }
}

Java:

@org.xwalk.core.JavascriptInterface
public String TestCallback(String someData, String onSuccess, String onError){
   xwalk.evaluateJavascript("getCallback(" + onSuccess + ")('success');", null);
}

Using this with JavaScript:

var onSuccess = registerCallback(function(r) {
   console.log(r);
});

TestCallback('lalala', onSuccess, null);

Using a JavaScript callback function as a parameter for the addJavascriptInterface method in Java

Answer №1

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