Bindings - providing callback to Objective-C method which expects a Selector?

JamesLavery

In my binding library I've got an Objective-C selector:

/**
 * postGetBattery
 * Creates a SktScanObject and initializes it to perform a request for the
 * battery level in the scanner.
 */
-(void)postGetBattery:(DeviceInfo*)deviceInfo Target:(id)target Response:(SEL)response;

which I've bound as follows:

[Export ("postGetBattery:Target:Response:")]
void PostGetBattery (DeviceInfo deviceInfo, NSObject target, Selector response);

My problem now is how I call this in my Xamarin.iOS application - providing the resonse selector. Creating a C# method with what looks like the right signature:

    void onPostGetBatteryResponse (long result, ISktScanObject scanObject)
    {
        if (!SktScanErrors.SKTSUCCESS ((int)result)) {
            throw new Exception (string.Format ("Error in onPostGetBatteryResponse: result={0}", result));
        }
    }

Produces the error:

/Users/james/P4/Novex Error CS1503: Argument `#3' cannot convert `method group' expression to type `MonoTouch.ObjCRuntime.Selector' (CS1503)

so presumably I have to either change/enhance my binding or create a selector associated with my callback method.

Can someone enlighten me please?

adamkemp

A selector is just like a method name. It's not an actual method. You have to do something like this:

private const string PostGetBatteryResponseSelectorName = "postGetBatteryResponseWithResult:scanObject:";
private static readonly Selector PostGetBatteryResponseSelector = new Selector(PostGetBatteryResponseSelectorName);

[Export(PostGetBatteryResponseSelectorName)]
private void onPostGetBatteryResponse (long result, ISktScanObject scanObject)
{
    if (!SktScanErrors.SKTSUCCESS ((int)result)) {
        throw new Exception (string.Format ("Error in onPostGetBatteryResponse: result={0}", result));
    }
}

private void SomeOtherMethod()
{
    MethodThatWantsATargetAndSelector(this, PostGetBatteryResponseSelector);
}

The error, I believe, is actually in your equivalent to that last bit of code. You can't pass onPostGetBatteryResponse to a function expecting a target and selector. You have to pass the target (your object) and a Selector object that matches the Export attribute.

Also make sure that the class containing this code inherits (directly or indirectly) from NSObject.

adamkemp

A selector is just like a method name. It's not an actual method. You have to do something like this:

private const string PostGetBatteryResponseSelectorName = "postGetBatteryResponseWithResult:scanObject:";
private static readonly Selector PostGetBatteryResponseSelector = new Selector(PostGetBatteryResponseSelectorName);

[Export(PostGetBatteryResponseSelectorName)]
private void onPostGetBatteryResponse (long result, ISktScanObject scanObject)
{
    if (!SktScanErrors.SKTSUCCESS ((int)result)) {
        throw new Exception (string.Format ("Error in onPostGetBatteryResponse: result={0}", result));
    }
}

private void SomeOtherMethod()
{
    MethodThatWantsATargetAndSelector(this, PostGetBatteryResponseSelector);
}

The error, I believe, is actually in your equivalent to that last bit of code. You can't pass onPostGetBatteryResponse to a function expecting a target and selector. You have to pass the target (your object) and a Selector object that matches the Export attribute.

Also make sure that the class containing this code inherits (directly or indirectly) from NSObject.

JamesLavery

Adam,
Thanks, that's just what I needed to know - to decorate the method with the correct Export.