Event handlers context (v7)

Question

I'm also getting trouble with event handlers context because unlike 6.3, "this" in event handlers
is now the event itself (which is not only a redondant, but also prevents accessing the instance
in which the function is defined).



For example:

function ExampleClass(){}


// Event handler
ExampleClass.prototype.onclick = function(e){
    console.log(this);
    console.log('Hello= ' + this.hello);
};


// Create two different instances of the Test object
var obj1 = new ExampleClass();
obj1.hello = 123;

var obj2 = new ExampleClass();
obj2.hello = 234;


// In this case, "this" is the Test instance
obj1.onclick(null);
obj2.onclick(null);


// In this case, "this" is the event (same value as "e")
// therefore it cannot access the property "hello" of the instance.
Microsoft.Maps.Events.addHandler(map, 'click', obj1.onclick);
Microsoft.Maps.Events.addHandler(map, 'click', obj2.onclick);




The event handler cannot access "hello" because it has no reference to the matching ExampleClass object, so how can the callback function possibly access instance properties from the event handler ?

Answer 1

For 7.1, I would suggest adding a 4th parameter to "Microsoft.Maps.Events.addHandler " that allows passing additional parameters to the event handler.

Answer 2

How about wrapping your class and doing something like this:

 

var ExampleClass = function(param){
	var p = param;
	
	return function(e){
		alert("Hello " + p);
	};
};

var obj1 = new ExampleClass("Ricky");
var obj2 = new ExampleClass("Bob");

Microsoft.Maps.Events.addHandler(map, 'click', obj1);
Microsoft.Maps.Events.addHandler(map, 'click', obj2);

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Windows Live Developer MVP - http://rbrundritt.spaces.live.com | http://inknowledge.co.uk