How do you use respondsToSelector & performSelector in PyObjc

Question

I'm converting a Objective-C program to PyObjC and lack experience in both.

Here is the Objective-C portion

WebPreferences *p = [webview preferences];
if([p respondsToSelector:@selector(setWebGLEnabled:)]){
[p performSelector:@selector(setWebGLEnabled:) withObject:[NSNumber numberWithBool:YES]];
}

This is basically an undocumented method (yes I know I can't submit to app store) to enable WebGL in the WebView

I can't figure out how to translate this portion to PyObjC

Is this at all useful? http://lethain.com/how-to-use-selectors-in-pyobjc/ — Joe McMahon, Feb 04 '14 at 01:23

score 1 · Answer 1 · answered Feb 04 '14 at 19:38

1

You don't have to use performSelector, just call the method:

p = webview.preferences()
p.setWebGLEnabled_(True)

This works because PyObjC doesn't look at header files but at the Objective-C runtime to find out which methods are present.

answered Feb 04 '14 at 19:38

Ronald Oussoren

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Doesn't this still throw a Cocoa exception if `setWebGLEnabled_` doesn't exist on `p`? – jscs Feb 10 '14 at 05:27
It does. You can avoid that by using “hasattr”. – Ronald Oussoren Feb 10 '14 at 08:15
I am curious then, what makes you prefer the Python version of "Does this method exist? Then call it." over Cocoa's here? – jscs Feb 10 '14 at 20:52
I prefer the Python version because that gives (IMHO) cleaner code. – Ronald Oussoren Feb 11 '14 at 08:14
Fair enough. Python is, probably without exception, more satisfactory in the "elegance" department than ObjC. – jscs Feb 11 '14 at 08:15

score 0 · Answer 2 · answered Feb 04 '14 at 01:50

One of the magic bits of the bridge. You can just use the selector's string -- the method name (with colons, not underscores):

>>> from AppKit import *
>>> s = NSString.stringWithString_("Lemon curry?")
>>> s.respondsToSelector_("length")
True
>>> s.respondsToSelector_("count")
False
>>> s.respondsToSelector_("writeToFile:atomically:encoding:error:")
True
>>> s.performSelector_("lowercaseString")
u'lemon curry?'

How do you use respondsToSelector & performSelector in PyObjc

2 Answers2