{"id":3668,"date":"2013-03-25T17:45:25","date_gmt":"2013-03-26T00:45:25","guid":{"rendered":"http:\/\/blog.xamarin.com\/?p=3668"},"modified":"2019-07-03T10:12:00","modified_gmt":"2019-07-03T17:12:00","slug":"producing-better-bindings-3-selectors","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/xamarin\/producing-better-bindings-3-selectors\/","title":{"rendered":"Producing Better Bindings #3: Selectors"},"content":{"rendered":"

\t\t\t\tThis blog post is about producing better bindings of Objective-C libraries for Xamarin.iOS<\/a> and Xamarin.Mac<\/a>. Read the series introduction<\/a> to get a better idea why this is important and how it can save you time and headaches.<\/p>\n

What can go wrong ?<\/strong><\/p>\n

Binding selectors is largely done using the [Export(\"\")]<\/code> attribute. As such, it shares a lot of similarities with the\u00a0[Field]<\/code> attribute<\/a>\u2014including the main cause of issues: typos<\/strong>.<\/p>\n

In fact, the all time favorite<\/em>\u00a0issue is likely the infamous missing colon at the selector’s end (when parameters are used). For example, the following Objective-C method declaration:<\/p>\n

\n-(void) step: (ccTime) dt;\n<\/pre>\n
should be translated to:<\/p>\n
\n[Export ("step:")] \/\/ without the ':' this method won't work\nvoid Step (float deltaTime);\n<\/pre>\n
However, it is also a common error to forget the [Static]<\/code> attribute when a selector starts with a plus sign (+<\/code>)\u00a0character. The Objective-C static method declaration:<\/p>\n
\n+(id) actionWithDuration:(ccTime)duration angle:(float)angle;\n<\/pre>\n
should be translated to:<\/p>\n
\ninterface CCRotateBy {\n\t[Static] \/\/ easy to forget, unusable without it!\n\t[Export ("actionWithDuration:angle:")]\n\tCCRotateBy Create (float duration, float deltaAngle);\n\t\/\/ ...\n}\n<\/pre>\n
A less common issue is\u00a0wrong<\/em> builds. Your bindings might include selectors that are not part of the native library binary (e.g. missing source files, wrong defines\u2026) even if they are documented and present in the header files.<\/p>\n
Finally, some library updates might introduce breaking changes, including removed API entry points. If you only bind new APIs, you might be shipping old, missing, APIs without realizing it.<\/p>\n
What can we check for ?<\/strong><\/p>\n
Quite a few things, including:<\/p>\n